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Tawfilas M, Bartolini Torres G, Lorenzi R, Saibene M, Mauri M, Simonutti R. Transparent and High-Refractive-Index Titanium Dioxide/Thermoplastic Polyurethane Nanocomposites. ACS OMEGA 2024; 9:29339-29349. [PMID: 39005776 PMCID: PMC11238196 DOI: 10.1021/acsomega.4c01053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Revised: 05/02/2024] [Accepted: 05/27/2024] [Indexed: 07/16/2024]
Abstract
Transparent nanocomposite films made of surface-modified titanium dioxide nanoparticles and thermoplastic polyurethane are prepared via film casting approach showing enhanced refractive indexes and mechanical properties. Two different sets of composites were prepared up to 37.5 wt % of inorganic nanoparticles with a diameter <15 nm, one set using particles capped only with oleic acid and a second one with a bimodal system layer made of oleic acid and mPEO-5000 as coating agents. All of the composites show significantly enhanced refractive index and mechanical properties than the neat polymeric matrix. The transparency of nanocomposite films shows the excellent dispersion of the inorganic nanoparticles in the polymeric matrix avoiding aggregation and precipitation phenomena. Our study provides a facile and feasible route to produce transparent nanocomposite films with tunable mechanical properties and high refractive indices for various applications.
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Affiliation(s)
- Massimo Tawfilas
- Department of Materials Science, University of Milano-Bicocca, Via Roberto Cozzi 55, 20125 Milano, Italy
| | - Gianluca Bartolini Torres
- Department of Materials Science, University of Milano-Bicocca, Via Roberto Cozzi 55, 20125 Milano, Italy
| | - Roberto Lorenzi
- Department of Materials Science, University of Milano-Bicocca, Via Roberto Cozzi 55, 20125 Milano, Italy
| | - Melissa Saibene
- Piattaforma
di Microscopia, University of Milano-Bicocca, 20126 Milano, Italy
| | - Michele Mauri
- Department of Materials Science, University of Milano-Bicocca, Via Roberto Cozzi 55, 20125 Milano, Italy
| | - Roberto Simonutti
- Department of Materials Science, University of Milano-Bicocca, Via Roberto Cozzi 55, 20125 Milano, Italy
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2
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Wang B, Gao K, Wang K, Wang Y, Chang Q, Yang H. Induced Decomposition and Slip Interface Transformation of Oleic Acid Enables Ultralow Wear in Boundary Lubrication. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:1941-1949. [PMID: 38207337 DOI: 10.1021/acs.langmuir.3c03767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2024]
Abstract
The tribological behavior of carboxylic acids, especially oleic acid, in boundary lubrication conditions is a subject of interest. This study presents the results of four-ball tribological tests conducted under varying contact pressures and sliding speeds. The findings reveal a critical turning speed within a confined zone, which causes a significant change in the frictional performances of oleic acid, leading to the formation of an ultralow wear tribofilm. This tribofilm, predominantly composed of oxyhydrogen compounds and hydrocarbons with more than five carbon atoms, is generated by the molecular action of oleic acid. Reactive nonequilibrium molecular dynamics simulations demonstrate that the shear speed-dependent decomposition modes of oleic acid and the transformation of the lubrication slip interface are the fundamental processes underlying the formation of this ultralow-wear boundary tribofilm.
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Affiliation(s)
- Bin Wang
- School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
| | - Kai Gao
- Institute of New Materials and Advanced Manufacturing, Beijing Academy of Science and Technology, Beijing 100084, China
| | - Kai Wang
- School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
| | - Yujie Wang
- Scientific and Technological Innovation Center, Beijing 100012, China
| | - Qiuying Chang
- School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
| | - He Yang
- Research Institute of Petroleum Processing, Sinopec, Beijing 100083, China
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3
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Wei P, Gao P, Yang J, Pu W. Investigating the Behavior of Various Lubrication Regimes under Dynamic Conditions Using Nonequilibrium Molecular Dynamics. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:12365-12383. [PMID: 37611147 DOI: 10.1021/acs.langmuir.3c01468] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
It is crucial to comprehend how the oil film varies under dynamic operating conditions and the accompanying friction properties to better grasp the friction mechanism and control friction behavior. To model the friction characteristics under boundary lubrication (BL) and elastohydrodynamic lubrication (EHL), nonequilibrium molecular dynamics simulations with various numbers of hexadecane molecules as lubricating oil were conducted in this research under the conditions of dynamic speed and dynamic load. All the dynamic operating conditions have the form of sine waves, with various frequencies and amplitudes. According to the findings, the friction force is strongly connected with interfaces where relative sliding takes place, whose number, velocity difference, and the degree of solidification have significant influences. The variation of amplitude under dynamic load can cause a regular change in the density of the lubricating layer, while the variation of frequency can cause a change in molecular layer's range of motion. Both effects are crucial for friction. The structure of the lubricating layer with lower friction varies with various frequencies for dynamic velocity. Both high and small amplitudes of velocity offer advantages to form a stable film structure at low frequencies in the BL and EHL regions, while the amplitude in the BL area has minimal association with friction at high frequencies. At high frequencies in the EHL region, the friction rises as the amplitude of velocity grows and the lubricating layer becomes more unstable.
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Affiliation(s)
- Pengchong Wei
- School of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China
| | - Pan Gao
- School of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China
| | - Jialong Yang
- School of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China
| | - Wei Pu
- School of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China
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4
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Weiand E, Rodriguez-Ropero F, Roiter Y, Koenig PH, Angioletti-Uberti S, Dini D, Ewen JP. Effects of surfactant adsorption on the wettability and friction of biomimetic surfaces. Phys Chem Chem Phys 2023; 25:21916-21934. [PMID: 37581271 DOI: 10.1039/d3cp02546b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/16/2023]
Abstract
The properties of solid-liquid interfaces can be markedly altered by surfactant adsorption. Here, we use molecular dynamics (MD) simulations to study the adsorption of ionic surfactants at the interface between water and heterogeneous solid surfaces with randomly arranged hydrophilic and hydrophobic regions, which mimic the surface properties of human hair. We use the coarse-grained MARTINI model to describe both the hair surfaces and surfactant solutions. We consider negatively-charged virgin and bleached hair surface models with different grafting densities of neutral octadecyl and anionic sulfonate groups. The adsorption of cationic cetrimonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) surfactants from water are studied above the critical micelle concentration. The simulated adsorption isotherms suggest that cationic surfactants adsorb to the surfaces via a two-stage process, initially forming monolayers and then bilayers at high concentrations, which is consistent with previous experiments. Anionic surfactants weakly adsorb via hydrophobic interactions, forming only monolayers on both virgin and medium bleached hair surfaces. We also conduct non-equilibrium molecular dynamics simulations, which show that applying cationic surfactant solutions to bleached hair successfully restores the low friction seen with virgin hair. Friction is controlled by the combined surface coverage of the grafted lipids and the adsorbed CTAB molecules. Treated surfaces containing monolayers and bilayers both show similar friction, since the latter are easily removed by compression and shear. Further wetting MD simulations show that bleached hair treated with CTAB increases the hydrophobicity to similar levels seen for virgin hair. Treated surfaces containing CTAB monolayers with the tailgroups pointing predominantly away from the surface are more hydrophobic than bilayers due to the electrostatic interactions between water molecules and the exposed cationic headgroups.
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Affiliation(s)
- Erik Weiand
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK.
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
| | - Francisco Rodriguez-Ropero
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | - Yuri Roiter
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | - Peter H Koenig
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | - Stefano Angioletti-Uberti
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Department of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
| | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK.
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
| | - James P Ewen
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK.
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
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5
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Weiand E, Ewen JP, Roiter Y, Koenig PH, Page SH, Rodriguez-Ropero F, Angioletti-Uberti S, Dini D. Nanoscale friction of biomimetic hair surfaces. NANOSCALE 2023; 15:7086-7104. [PMID: 36987934 DOI: 10.1039/d2nr05545g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
We investigate the nanoscale friction between biomimetic hair surfaces using chemical colloidal probe atomic force microscopy experiments and nonequilibrium molecular dynamics simulations. In the experiments, friction is measured between water-lubricated silica surfaces functionalised with monolayers formed from either octadecyl or sulfonate groups, which are representative of the surfaces of virgin and ultimately bleached hair, respectively. In the simulations, friction is monitored between coarse-grained model hair surfaces with different levels of chemical damage, where a specified amount of grafted octadecyl groups are randomly replaced with sulfonate groups. The sliding velocity dependence of friction in the simulations can be described using an extended stress-augmented thermally activation model. As the damage level increases in the simulations, the friction coefficient generally increases, but its sliding velocity-dependence decreases. At low sliding velocities, which are closer to those encountered experimentally and physiologically, we observe a monotonic increase of the friction coefficient with damage ratio, which is consistent with our new experiments using biomimetic surfaces and previous ones using real hair. This observation demonstrates that modified surface chemistry, rather than roughness changes or subsurface damage, control the increase in nanoscale friction of bleached or chemically damaged hair. We expect the methods and biomimetic surfaces proposed here to be useful to screen the tribological performance of hair care formulations both experimentally and computationally.
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Affiliation(s)
- Erik Weiand
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK.
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
| | - James P Ewen
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK.
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
| | - Yuri Roiter
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | - Peter H Koenig
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | - Steven H Page
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | - Francisco Rodriguez-Ropero
- Corporate Functions Analytical and Data & Modeling Sciences, Mason Business Center, The Procter and Gamble Company, Mason, 45040 Ohio, USA
| | | | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK.
- Institute of Molecular Science and Engineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
- Thomas Young Centre for the Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, UK
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6
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Vuorte M, Kuitunen S, Van Tassel PR, Sammalkorpi M. Equilibrium state model for surfactants in oils: Colloidal assembly and adsorption. J Colloid Interface Sci 2023; 630:783-794. [DOI: 10.1016/j.jcis.2022.09.153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 09/29/2022] [Accepted: 09/30/2022] [Indexed: 11/11/2022]
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7
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Lu F, Du L, Chen W, Jiang H, Yang C, Pu Y, Wu J, Zhu J, Chen T, Zhang X, Wu C. T 1- T 2 dual-modal magnetic resonance contrast-enhanced imaging for rat liver fibrosis stage. RSC Adv 2022; 12:35809-35819. [PMID: 36545112 PMCID: PMC9749127 DOI: 10.1039/d2ra05913d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Accepted: 12/02/2022] [Indexed: 12/16/2022] Open
Abstract
The development of an effective method for staging liver fibrosis has always been a hot topic of research in the field of liver fibrosis. In this paper, PEGylated ultrafine superparamagnetic iron oxide nanocrystals (SPIO@PEG) were developed for T 1-T 2 dual-modal contrast-enhanced magnetic resonance imaging (MRI) and combined with Matrix Laboratory (MATLAB)-based image fusion for staging liver fibrosis in the rat model. Firstly, SPIO@PEG was synthesized and characterized with physical and biological properties as a T 1-T 2 dual-mode MRI contrast agent. Secondly, in the subsequent MR imaging of liver fibrosis in rats in vivo, conventional T 1 and T 2-weighted imaging, and T 1 and T 2 mapping of the liver pre- and post-intravenous administration of SPIO@PEG were systematically collected and analyzed. Thirdly, by creative design, we fused the T 1 and T 2 mapping images by MATLAB and quantitively measured each rat's hepatic fibrosis positive pixel ratio (PPR). SPIO@PEG was proved to have an ultrafine core size (4.01 ± 0.16 nm), satisfactory biosafety and T 1-T 2 dual-mode contrast effects under a 3.0 T MR scanner (r 2/r 1 = 3.51). According to the image fusion results, the SPIO@PEG contrast-enhanced PPR shows significant differences among different stages of liver fibrosis (P < 0.05). The combination of T 1-T 2 dual-modal SPIO@PEG and MATLAB-based image fusion technology could be a promising method for diagnosing and staging liver fibrosis in the rat model. PPR could also be used as a non-invasive biomarker to diagnose and discriminate the stages of liver fibrosis.
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Affiliation(s)
- Fulin Lu
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China,Department of Radiology, Sichuan Academy of Medical Sciences, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of ChinaChengdu 610072China
| | - Liang Du
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Wei Chen
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Hai Jiang
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Chenwu Yang
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Yu Pu
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Jun Wu
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Jiang Zhu
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Tianwu Chen
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Xiaoming Zhang
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
| | - Changqiang Wu
- Medical Imaging Key Laboratory of Sichuan Province, School of Medical Imaging, Affiliated Hospital of North Sichuan Medical CollegeNanchong 637000China
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8
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Motozuka S, Sato H, Kuwata H, Bito M, Okazaki Y. Effects of interfacial interactions between metal and process control agents during ball milling on the microstructure of the milled Fe-based nanocrystalline alloy powder. Heliyon 2022; 8:e10325. [PMID: 36061032 PMCID: PMC9434051 DOI: 10.1016/j.heliyon.2022.e10325] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 08/01/2022] [Accepted: 08/12/2022] [Indexed: 10/26/2022] Open
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9
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Relating Dry Friction to Interdigitation of Surface Passivation Species: A Molecular Dynamics Study on Amorphous Carbon. MATERIALS 2022; 15:ma15093247. [PMID: 35591582 PMCID: PMC9103985 DOI: 10.3390/ma15093247] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 03/31/2022] [Accepted: 04/27/2022] [Indexed: 01/11/2023]
Abstract
Friction in boundary lubrication is strongly influenced by the atomic structure of the sliding surfaces. In this work, friction between dry amorphous carbon (a-C) surfaces with chemisorbed fragments of lubricant molecules is investigated employing molecular dynamic simulations. The influence of length, grafting density and polarity of the fragments on the shear stress is studied for linear alkanes and alcohols. We find that the shear stress of chain-passivated a-C surfaces is independent of the a-C density. Among all considered chain-passivated systems, those with a high density of chains of equal length exhibit the lowest shear stress. However, shear stress in chain-passivated a-C is consistently higher than in a-C surfaces with atomic passivation. Finally, surface passivation species with OH head groups generally lead to higher friction than their non-polar analogs. Beyond these qualitative trends, the shear stress behavior for all atomic- and chain-passivated, non-polar systems can be explained semi-quantitatively by steric interactions between the two surfaces that cause resistance to the sliding motion. For polar passivation species electrostatic interactions play an additional role. A corresponding descriptor that properly captures the interlocking of the two surfaces along the sliding direction is developed based on the maximum overlap between atoms of the two contacting surfaces.
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Chen X, Yang J, Yasuda K, Koga N, Zhang H. Adsorption Behavior of TEMPO-Based Organic Friction Modifiers during Sliding between Iron Oxide Surfaces: A Molecular Dynamics Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:3170-3179. [PMID: 35235329 DOI: 10.1021/acs.langmuir.1c03203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Organic friction modifiers (OFMs) added to lubricating oils to reduce friction and wear are crucial for reducing energy loss and CO2 emissions. In our previous studies, we have developed N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecaneamide, referred to as C12TEMPO, as a new type of OFM and experimentally demonstrated its superior performance to conventional OFMs of stearic acid and glycerol monooleate. However, the behavior of C12TEMPO adsorbing onto solid surfaces from base oil during sliding, which largely dictates the lubrication performance, is yet to be elucidated. Here, we performed molecular dynamics simulations for confined shear of a C12TEMPO solution in poly-α-olefin between hematite surfaces. Unlike conventional OFMs, which typically have one functional group or multiple functional groups of the same type, C12TEMPO features two functional groups of different types: one amide and one terminal free oxygen radical. The results showed that adsorbed boundary films with a double-layer structure form stably during sliding, owing to double- or single-site surface adsorption and interlayer hydrogen bonding via the two functional groups. Additionally, some molecules in each of the first and second layers also form intralayer hydrogen bonding. Such multitype adsorption is unique and favorable for enhancing the strength of boundary films to withstand heavily loaded and prolonged sliding. The velocity distribution indicates that the first and second layers are solid- and liquid-like, respectively. The second layer could act as a buffer for the first layer, which is the last barrier to prevent solid-solid contact, against shear. We also found that the second layer can act as a reservoir to rapidly repair the once depleted region in the first layer because of the interlayer hydrogen bonding. The combination of the high strength and self-repair ability of the C12TEMPO boundary films can rationally explain the experimentally observed properties of high load-carrying capacity, excellent antiwear effect, and high stability of friction over time.
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Affiliation(s)
- Xingyu Chen
- Department of Complex Systems Science, Graduate School of Informatics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Juntao Yang
- Department of Complex Systems Science, Graduate School of Informatics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Koji Yasuda
- Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Nobuaki Koga
- Department of Complex Systems Science, Graduate School of Informatics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Hedong Zhang
- Department of Complex Systems Science, Graduate School of Informatics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
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11
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Watanabe S, Tadokoro C, Miyake K, Sasaki S, Nakano K. Processes of molecular adsorption and ordering enhanced by mechanical stimuli under high contact pressure. Sci Rep 2022; 12:3870. [PMID: 35264645 PMCID: PMC8907199 DOI: 10.1038/s41598-022-07854-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 02/24/2022] [Indexed: 11/09/2022] Open
Abstract
Adsorbed molecular films, referred to as boundary films in tribology, are widely used in various industrial products as a keyway for surface functionalisation, such as lubricity, wettability, and adhesion. Because boundary films are thin nanometre-scale molecular layers and can easily be removed, their formation process cannot be elucidated in detail. In this study, to analyse the growth dynamics of boundary films, the film thickness and molecular orientation of the boundary film of a fatty acid used as an additive in rolling contact as mechanical stimuli were measured in situ. The measurements were performed on simple test lubricants, which were composed of n-hexadecane and stearic acid, at rolling tribological condition between steel and glass (or sapphire) surfaces by ultrathin film interferometry combined with sum-frequency generation spectroscopy according to a unique protocol. The results quantitatively demonstrate shear-induced boundary film formation. The insight gained from these results is anticipated to enable the formulation of high-performance lubricant additives to further reduce friction loss and high-performance glues that can be freely designed for removability.
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Affiliation(s)
- Seiya Watanabe
- Department of Mechanical Engineering, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan.
| | - Chiharu Tadokoro
- Department of Mechanical Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
| | - Koji Miyake
- Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba, Ibaraki, 305-8564, Japan
| | - Shinya Sasaki
- Department of Mechanical Engineering, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan
| | - Ken Nakano
- Faculty of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama, 240-8501, Japan
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12
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Vuorte M, Kuitunen S, Sammalkorpi M. Physisorption of bio oil nitrogen compounds onto montmorillonite. Phys Chem Chem Phys 2021; 23:21840-21851. [PMID: 34554171 DOI: 10.1039/d1cp01880a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We assess computationally the adsorption of a series of nitrogen containing heterocycles and fatty acid amides from bio-oil on a model clay surface, Na-montmorillonite. The adsorption energies and conformations predicted by atomistic detail molecular dynamics (MD) simulations are compared against density functional theory (DFT) based molecular electrostatic potentials (MEP) and Hirshfeld, AIM, Merz-Singh-Kollman, and ChelpG charges. MD predicts systematically adsorption via cation bridging with adsorption strength of the heterocycles following purine > pyridine > imidazole > pyrrole > indole > quinoline. The fatty acid amides adsorption strength follows the steric availability and bulkiness of the head group. A comparison against the DFT calculations shows that MEP predicts adsorption geometries and the MD simulations reproduce the conformations for single adsorption site species. However, the DFT derived charge distibutions show that MD force-fields with non-polarizable fixed partial charge representations parametrized for aqueous environments cannot be used in apolar solvent environments without careful accuracy considerations. The overall trends in adsorption energies are reproduced by the Charmm GenFF employed in the MD simulations but the adsorption energies are systematically overestimated in this apolar solvent environment. The work has significance both for revealing nitrogen compound adsorption trends in technologically relevant bio oil environments but also as a methodological assessment revealing the limits of state of the art biomolecular force-fields and simulation protocols in apolar bioenvironments.
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Affiliation(s)
- Maisa Vuorte
- Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland.
| | - Susanna Kuitunen
- Neste Engineering Solutions Oy, P.O. Box 310, FI-06101 Porvoo, Finland
| | - Maria Sammalkorpi
- Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland. .,Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland
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13
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Rey J, Blanck S, Clabaut P, Loehlé S, Steinmann SN, Michel C. Transferable Gaussian Attractive Potentials for Organic/Oxide Interfaces. J Phys Chem B 2021; 125:10843-10853. [PMID: 34533310 DOI: 10.1021/acs.jpcb.1c05156] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Organic/oxide interfaces play an important role in many areas of chemistry and in particular for lubrication and corrosion. Molecular dynamics simulations are the method of choice for providing complementary insight to experiments. However, the force fields used to simulate the interaction between molecules and oxide surfaces tend to capture only weak physisorption interactions, discarding the stabilizing Lewis acid/base interactions. We here propose a simple complement to the straightforward molecular mechanics description based on "out-of-the-box" Lennard-Jones potentials and electrostatic interactions: the addition of an attractive Gaussian potential between reactive sites of the surface and heteroatoms of adsorbed organic molecules, leading to the Gaussian Lennard-Jones (GLJ) potential. The interactions of four oxygenated and four amine molecules with the typical and widespread hematite and γ-alumina surfaces are investigated. The root mean square deviation (RMSD) for all probed molecules is only 5.7 kcal/mol, which corresponds to an error of 23% over hematite. On γ-alumina, the RMSD is 11.2 kcal/mol using a single parameter for all five chemically inequivalent surface aluminum atoms. Applying GLJ to the simulation of organic films on oxide surfaces demonstrates that the mobility of the surfactants is overestimated by the simplistic LJ potential, while GLJ and other qualitatively correct potentials show a strong structuration and slow dynamics of the surface films, as could be expected from the first-principles adsorption energies for model head groups.
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Affiliation(s)
- Jérôme Rey
- Université de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5182, Laboratoire de Chimie, 46 allée d'Italie, Lyon F69364, France
| | - Sarah Blanck
- Université de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5182, Laboratoire de Chimie, 46 allée d'Italie, Lyon F69364, France.,Total Marketing & Services, Chemin du Canal-BP 22, Solaize 69360, France
| | - Paul Clabaut
- Université de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5182, Laboratoire de Chimie, 46 allée d'Italie, Lyon F69364, France
| | - Sophie Loehlé
- Total Marketing & Services, Chemin du Canal-BP 22, Solaize 69360, France
| | - Stephan N Steinmann
- Université de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5182, Laboratoire de Chimie, 46 allée d'Italie, Lyon F69364, France
| | - Carine Michel
- Université de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5182, Laboratoire de Chimie, 46 allée d'Italie, Lyon F69364, France
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14
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Rana R, Bavisotto R, Hou K, Tysoe WT. Surface chemistry at the solid-solid interface: mechanically induced reaction pathways of C 8 carboxylic acid monolayers on copper. Phys Chem Chem Phys 2021; 23:17803-17812. [PMID: 34397054 DOI: 10.1039/d1cp03170h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Mechano- or tribochemical processes are often induced by the large pressures, of the order of 1 GPa, exerted at contacting asperities at the solid-solid interface. These tribochemical process are not very well understood because of the difficulties of probing surface-chemical reaction pathways occurring at buried interfaces. Here, strategies for following surface reaction pathways in detail are illustrated for the tribochemical decomposition of 7-octenoic and octanoic acid adsorbed on copper. The chemistry was measured in ultrahigh vacuum by sliding either a tungsten carbide ball or a silicon atomic force microscope (AFM) tip over the surface to test a previous proposal that the nature of the terminal group in the carboxylic acid, vinyl versus alkyl, could influence its binding to the counterface, and therefore the reaction rate. The carboxylic acids bind strongly to the copper substrate as carboxylates to expose the hydrocarbon terminus. The tribochemical reaction rate was found to be independent of the nature of the hydrocarbon terminus, although the pull-off and friction forces measured by the AFM were different. The tribochemical reaction is initiated in the same way as the thermal reaction, by the carboxylate group tilting to eliminate carbon dioxide and deposit alkyl species onto the surface. This reaction occurs thermally at ∼640 K, but tribochemically at room temperature, producing significant differences in the rates and selectivities of the subsequent decomposition pathways of the adsorbed products.
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Affiliation(s)
- Resham Rana
- Department of Chemistry and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
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15
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Gao H, Ewen JP, Hartkamp R, Müser MH, Dini D. Scale-Dependent Friction-Coverage Relations and Nonlocal Dissipation in Surfactant Monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:2406-2418. [PMID: 33545003 DOI: 10.1021/acs.langmuir.0c03403] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Surfactant molecules, known as organic friction modifiers (OFMs), are routinely added to lubricants to reduce friction and wear between sliding surfaces. In macroscale experiments, friction generally decreases as the coverage of OFM molecules on the sliding surfaces increases; however, recent nanoscale experiments with sharp atomic force microscopy (AFM) tips have shown increasing friction. To elucidate the origin of these opposite trends, we use nonequilibrium molecular dynamics (NEMD) simulations and study kinetic friction between OFM monolayers and an indenting nanoscale asperity. For this purpose, we investigate various coverages of stearamide OFMs on iron oxide surfaces and silica AFM tips with different radii of curvature. We show that the differences between the friction-coverage relations from macroscale and nanoscale experiments are due to molecular plowing in the latter. For our small tip radii, the friction coefficient and indentation depth both have a nonmonotonic dependence on OFM surface coverage, with maxima occurring at intermediate coverage. We rationalize the nonmonotonic relations through a competition of two effects (confinement and packing density) that varying the surface coverage has on the effective stiffness of the OFM monolayers. We also show that kinetic friction is not very sensitive to the sliding velocity in the range studied, indicating that it originates from instabilities. Indeed, we find that friction predominately originates from plowing of the monolayers by the leading edge of the tip, where gauche defects are created, while thermal dissipation is mostly localized in molecules toward the trailing edge of the tip, where the chains return to a more extended conformation.
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Affiliation(s)
- Hongyu Gao
- Department of Materials Science and Engineering, Universität des Saarlandes, 66123 Saarbrücken, Germany
| | - James P Ewen
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
| | - Remco Hartkamp
- Process and Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands
| | - Martin H Müser
- Department of Materials Science and Engineering, Universität des Saarlandes, 66123 Saarbrücken, Germany
| | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
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16
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Hama T, Kouchi A, Watanabe N, Shioya N, Shimoaka T, Hasegawa T. In vivo characterization of the structures of films of a fatty acid and an alcohol adsorbed on the skin surface. Biophys Chem 2020; 266:106459. [PMID: 32835910 DOI: 10.1016/j.bpc.2020.106459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 08/13/2020] [Accepted: 08/14/2020] [Indexed: 11/17/2022]
Abstract
An in vivo analysis of stearyl alcohol and stearic acid films on the skin surface using polarized infrared-external reflection spectroscopy revealed that whether the sample molecules adopt an energetically stable conformation and orientation strongly depends on the molecular functionalities and sample preparation conditions. For stearic acid, even the difference in solute concentration between 0.1 and 0.5 wt% results in a different molecular conformation and orientation. This illustrates that the molecular organization of the adsorbate on the skin surface is sensitively determined by the kinetics of the sample film growth, not by the simple thermodynamic equilibrium with the skin temperature.
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Affiliation(s)
- Tetsuya Hama
- Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan; Department of Basic Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan.
| | - Akira Kouchi
- Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
| | - Naoki Watanabe
- Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
| | - Nobutaka Shioya
- Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Takafumi Shimoaka
- Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Takeshi Hasegawa
- Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
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17
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Shi J, Zhou Q, Sun K, Liu G, Zhou F. Understanding Adsorption Behaviors of Organic Friction Modifiers on Hydroxylated SiO 2 (001) Surfaces: Effects of Molecular Polarity and Temperature. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8543-8553. [PMID: 32610909 DOI: 10.1021/acs.langmuir.0c01386] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Molecular dynamics simulations are used to investigate the physisorption of organic friction modifiers (OFMs) lubricated by 1-decene trimer (PAO4) representing a base oil and confined between hydroxylated SiO2 (001) surfaces. The results indicate that OFM molecules form dense, tendentiously vertical monolayer films at low temperature but loose adsorption layers at high temperature, particularly for R-NH2 with weaker molecular polarity. The structural information is quantitatively clarified by mass density profiles, radial distribution function, and probability distributions of an end-to-end distance at a perpendicular-to-surface direction. The movement performance of lubricant, reflected by the thickness of the organic part and radius of gyration of PAO4 molecules, strongly depends on temperature. The adsorption amount of OFM molecules decreases dramatically with lowering OFM polarity and increasing temperature above the critical desorption temperatures of about 320, 373, and 453 K for amine (R-NH2), alcohol (R-OH), and acid (R-COOH), respectively. The interaction energies of the OFM-surface decrease continuously for the R-NH2 system with temperature and decrease rapidly as temperature exceeds a critical value for both R-OH and R-COOH systems. The single-molecule geometry optimization validates the significant role of the electrostatic and hydrogen-bond attractions in molecular adsorption. Therefore, the OFMs with stronger polarity (like R-COOH) present stronger adsorption and better temperature resistance. The findings in this work are of particular value and provide a guideline in designing and engineering novel OFM additives for extreme lubrication conditions.
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Affiliation(s)
- Junqin Shi
- State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi'an 710072, China
| | - Qing Zhou
- State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi'an 710072, China
| | - Kun Sun
- State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | - Guoqiang Liu
- State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi'an 710072, China
| | - Feng Zhou
- State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi'an 710072, China
- State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
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18
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Nazari M, Davoodabadi A, Huang D, Luo T, Ghasemi H. On interfacial viscosity in nanochannels. NANOSCALE 2020; 12:14626-14635. [PMID: 32614001 DOI: 10.1039/d0nr02294b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Capillary driven transport of liquids in nanoscopic channels is an omnipresent phenomenon in nature and technology including fluid flow in the human body and plants, drug delivery, nanofluidic devices, and energy/water systems. However, the kinetics of this mass transport mechanism remains in question as the well-known Lucas-Washburn (LW) model predicts significantly faster flow rates compared to the experimental observations. We here showed the role of interfacial viscosity in capillary motion slowdown in nanochannels through a combination of experimental, analytical and molecular dynamics techniques. We showed that the slower liquid flow is due to the formation of a thin liquid layer adjacent to the channel walls with a viscosity substantially greater than the bulk liquid. By incorporating the effect of the interfacial layer, we presented a theoretical model that accurately predicts the capillarity kinetics in nanochannels of different heights. Non-equilibrium molecular dynamics simulation confirmed the obtained interfacial viscosities. The viscosities of isopropanol and ethanol within the interfacial layer were 9.048 mPa s and 4.405 mPa s, respectively (i.e. 279% and 276% greater than their bulk values). We also showed that the interfacial layers are 6.4 nm- and 5.3 nm-thick for isopropanol and ethanol, respectively.
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Affiliation(s)
- Masoumeh Nazari
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Rd, Houston, Texas 77204, USA.
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19
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Lavorato GC, Rubert AA, Xing Y, Das R, Robles J, Litterst FJ, Baggio-Saitovitch E, Phan MH, Srikanth H, Vericat C, Fonticelli MH. Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles. NANOSCALE 2020; 12:13626-13636. [PMID: 32558841 DOI: 10.1039/d0nr02069a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Magnetite (Fe3O4) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe3O4 nanomaterials gradually oxidize to maghemite (γ-Fe2O3) under conventional environmental conditions leading to changes in their functional properties that determine their performance in many applications. Here we propose a novel strategy to control the surface chemistry of monodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferrite epitaxial coating in core/shell nanostructures. We have carried out a combined Mössbauer spectroscopy, dc magnetometry, X-ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy study on iron oxide and Fe3O4/Zn0.6Fe2.4O4 core/shell nanoparticles aged under ambient conditions for 6 months. Our results reveal that while the aged iron oxide nanoparticles consist of a mixture of γ-Fe2O3 and Fe3O4, the Zn-ferrite-coating preserves a highly stoichiometric Fe3O4 core. Therefore, the aged core/shell nanoparticles present a sharp Verwey transition, an increased saturation magnetization and the possibility of tuning the effective anisotropy through exchange-coupling at the core/shell interface. The inhibition of the oxidation of the Fe3O4 cores can be accounted for in terms of the chemical nature of the shell layer and an epitaxial crystal symmetry matching between the core and the shell.
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Affiliation(s)
- Gabriel C Lavorato
- Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Universidad Nacional de La Plata - CONICET, 1900 La Plata, Buenos Aires, Argentina.
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20
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Cafolla C, Foster W, Voïtchovsky K. Lubricated friction around nanodefects. SCIENCE ADVANCES 2020; 6:eaaz3673. [PMID: 32284981 PMCID: PMC7124950 DOI: 10.1126/sciadv.aaz3673] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Accepted: 01/08/2020] [Indexed: 06/11/2023]
Abstract
The lubrication properties of nanoconfined liquids underpin countless natural and industrial processes. However, our current understanding of lubricated friction is still limited, especially for nonideal interfaces exhibiting nanoscale chemical and topographical defects. Here, we use atomic force microscopy to explore the equilibrium and dynamical behavior of a model lubricant, squalane, confined between a diamond tip and graphite in the vicinity of an atomic step. We combine high-resolution imaging of the interface with highly localized shear measurements at different velocities and temperatures to derive a quantitative picture of the lubricated friction around surface defects. We show that defects tend to promote local molecular order and increase friction forces by reducing the number of stable molecular configurations in their immediate vicinity. The effect is general, can propagate over hundreds of nanometers, and can be quantitatively described by a semiempirical model that bridges the molecular details and mesoscale observations.
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21
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Vuorte M, Vierros S, Kuitunen S, Sammalkorpi M. Adsorption of impurities in vegetable oil: A molecular modelling study. J Colloid Interface Sci 2020; 571:55-65. [PMID: 32179309 DOI: 10.1016/j.jcis.2020.03.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 01/22/2020] [Accepted: 03/04/2020] [Indexed: 12/27/2022]
Abstract
Here, the adsorption of impurity species from triglyceride solvent representing a model vegetable oil is studied using atomistic molecular dynamics simulations. We compare the adsorption of water, glycerol, oleic acid, monoolein, and two types of phospholipids on model silica adsorbents differing in their OH-group density, i.e. hydrogen bonding ability, quartz and cristobalite. We find that the species containing charged groups, phospholipids DOPC and DOPE, adsorb significantly stronger than the nonionic impurities. Secondary contribution to adsorption arises from hydrogen bonding capability of the impurity species, the silica surface, and also the triglyceride solvent: in general, more hydrogen bonding sites in impurity species leads to enhanced adsorption but hydrogen bonding with solvent competes for the available sites. Interestingly, adsorption is weaker on cristobalite even though it has a higher hydrogen bonding site density than quartz. This is because the hydrogen bonds can saturate each other on the adsorbent. The finding demonstrates that optimal adsorption response is obtained with intermediate adsorbent hydrogen bonding site densities. Additionally, we find that monoolein and oleic acid show a concentration driven adsorption response and reverse micelle like aggregate formation in bulk triglyceride solvent even in the absence of water. The findings offer insight into adsorption phenomena at inorganic adsorbent - apolar solvent interfaces and provide guidelines for enhanced design of adsorbent materials for example for vegetable oil purification.
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Affiliation(s)
- Maisa Vuorte
- Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland
| | - Sampsa Vierros
- Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland; Neste Engineering Solutions Oy, P.O. Box 310, FI-06101 Porvoo, Finland
| | - Susanna Kuitunen
- Neste Engineering Solutions Oy, P.O. Box 310, FI-06101 Porvoo, Finland
| | - Maria Sammalkorpi
- Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland; Department of Bioproducts and Biomaterials, School of Chemical Engineering, Aalto University, P.O. Box 16300, FI-00076 Aalto, Finland.
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22
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Prentice IJ, Liu X, Nerushev OA, Balakrishnan S, Pulham CR, Camp PJ. Experimental and simulation study of the high-pressure behavior of squalane and poly-α-olefins. J Chem Phys 2020; 152:074504. [PMID: 32087637 DOI: 10.1063/1.5139723] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The equation of state, dynamical properties, and molecular-scale structure of squalane and mixtures of poly-α-olefins at room temperature are studied with a combination of state-of-the-art, high-pressure experiments and molecular-dynamics simulations. Diamond-anvil cell experiments indicate that both materials are non-hydrostatic media at pressures above ∼1 GPa. The equation of state does not exhibit any sign of a first-order phase transition. High-pressure x-ray diffraction experiments on squalane show that there are no Bragg peaks, and hence, the apparent solidification occurs without crystallization. These observations are complemented by a survey of the equation of state and dynamical properties using simulations. The results show that molecular diffusion is essentially arrested above about 1 GPa, which supports the hypothesis that the samples are kinetically trapped in metastable amorphous-solid states. The shear viscosity becomes extremely large at very high pressures, and the coefficient governing its increase from ambient pressure is in good agreement with the available literature data. Finally, simulated radial distribution functions are used to explore the evolution of the molecular-scale structure with increasing pressure. Subtle changes in the short-range real-space correlations are related to a collapse of the molecular conformations with increasing pressure, while the evolution of the static structure factor shows excellent correlation with the available x-ray diffraction data. These results are of indirect relevance to oil-based lubricants, as the pressures involved are comparable to those found in engines, and hence, the ability of lubricating thin films to act as load-bearing media can be linked to the solidification phenomena studied in this work.
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Affiliation(s)
- Iain J Prentice
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Xiaojiao Liu
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Oleg A Nerushev
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Sashi Balakrishnan
- Global Lubricants Technology Research and Innovation, BP International Limited, Technology Centre, Whitchurch Hill, Pangbourne, Reading RG8 7QR, England
| | - Colin R Pulham
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Philip J Camp
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
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23
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Fry BM, Moody G, Spikes HA, Wong JSS. Adsorption of Organic Friction Modifier Additives. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:1147-1155. [PMID: 31941274 DOI: 10.1021/acs.langmuir.9b03668] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Organic friction modifier additives (OFMs) are surfactant molecules added to engine oils to reduce friction in the boundary lubrication regime. They are thought to work by forming an absorbed layer, which provides low friction. This paper studied the relationship between the adsorption of OFMs and their friction and wear-reducing properties in a rubbing contact formed by a stationary glass ball and a rotating silicon disk under the boundary lubrication regime. The effect of molecular structure was investigated by using OFMs of various tail saturation and head group chemistry. OFMs tested were oleic acid, octadecylamine, oleylamine, and glycerol monooleate. The thickness of an OFM-adsorbed layer in hexadecane, examined in situ by spectroscopic ellipsometry and quartz crystal microbalance (QCM), depends on the molecular structure and the concentration of the OFM. As expected, the saturated, linear chain gives the thickest film. A critical OFM layer thickness of about 0.6 nm is necessary to achieve low initial and maximum friction. The thicker OFM layers are accompanied by narrower wear tracks, which are rougher than the wider, smoother wear tracks formed with thinner OFM layers. The interplay between the thickness of the OFM layer and wear track surface roughness results in all OFM layers having similar steady state friction. This shows that the apparent effect of OFM depends on the stage of the rubbing test: initially on friction, and then subsequently on surface damage. Despite OFMs and the base oil having similar refractive indices, ellipsometry was found to be a suitable technique for examining the adsorption of OFM additives from an oil-based solution and showed reasonable correlation with QCM results.
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Affiliation(s)
- Benjamin M Fry
- Department of Mechanical Engineering , Imperial College London , London SW7 2AZ , U.K
| | - Gareth Moody
- Croda Lubricants , Croda Europe Ltd , Cowick Hall , Snaith , East Yorkshire DN14 9AA , U.K
| | - Hugh A Spikes
- Department of Mechanical Engineering , Imperial College London , London SW7 2AZ , U.K
| | - Janet S S Wong
- Department of Mechanical Engineering , Imperial College London , London SW7 2AZ , U.K
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24
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Greenfield ML, Ohtani H. Friction and normal forces of model friction modifier additives in simulations of boundary lubrication. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1670876] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
| | - Hiroko Ohtani
- Vehicle Manufacturing and Additive Manufacturing-Metals Department, Ford Motor Company, Dearborn, MI, USA
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25
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Huang D, Zhang T, Xiong G, Xu L, Qu Z, Lee E, Luo T. Tuning Water Slip Behavior in Nanochannels Using Self-Assembled Monolayers. ACS APPLIED MATERIALS & INTERFACES 2019; 11:32481-32488. [PMID: 31408315 DOI: 10.1021/acsami.9b09509] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Water slip at solid surfaces is important for a wide range of micro-/nanofluidic applications. While it is known that water slip behavior depends on surface functionalization, how it impacts the molecular level dynamics and mass transport at the interface is still not thoroughly understood. In this paper, we use nonequilibrium molecular dynamics simulations to investigate the slip behavior of water confined between gold surfaces functionalized by self-assembled monolayer (SAM) molecules with different polar functional groups. We observe a positive-to-negative slip transition from hydrophobic to hydrophilic SAM functionalizations, which is found to be related to the stronger interfacial interaction between water molecules and more hydrophilic SAM molecules. The stronger interaction increases the surface friction and local viscosity, making water slip more difficult. More hydrophilic functionalization also slows down the interfacial water relaxation and leads to more pronounced water trapping inside the SAM layer, both of which impede water slip. The results from this work will provide useful insights into the understanding of the water slip at functionalized surfaces and design guidelines for various applications.
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Affiliation(s)
| | | | - Guoping Xiong
- Department of Mechanical Engineering , University of Nevada - Reno , Reno , Nevada 89557 , United States
| | - Linji Xu
- Environmental Engineering Technology Research Center , Chongqing Academy of Ecology and Environmental Sciences , No. 252 Qishan Road , Yubei District, Chongqing 401120 , China
| | - Zhiguo Qu
- Moe Key Laboratory of Thermo-Fluid Science and Engineering, Energy and Power Engineering School , Xi'an Jiaotong University , Xi'an 710049 , China
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26
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An alternative model for simulating water between two monolayer surfaces. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.111284] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Tsagkaropoulou G, Warrens CP, Camp PJ. Interactions between Friction Modifiers and Dispersants in Lubricants: The Case of Glycerol Monooleate and Polyisobutylsuccinimide-Polyamine. ACS APPLIED MATERIALS & INTERFACES 2019; 11:28359-28369. [PMID: 31287656 DOI: 10.1021/acsami.9b05718] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The structural and frictional properties of 10 wt % solutions of the amphiphilic molecules glycerol monooleate (GMO) and polyisobutylsuccinimide-polyamine (PIBSA-PAM) in squalane are studied using molecular dynamics simulations in bulk and under confinement between iron oxide surfaces. GMO is a friction modifier, PIBSA-PAM is a dispersant, and squalane is a good model for typical base oils. A range of liquid compositions and applied pressures is explored, and the formation and stability of reverse micelles are determined under quiescent and shear conditions. Micellization is observed mainly in systems with a high GMO content, but PIBSA-PAM may also form small aggregates on its own. In the confined systems under both static and shear conditions, some surfactant molecules adsorb onto the surfaces, with the rest of the molecules forming micelles or aggregates. Shearing the liquid layer under high pressure causes almost all of the micelles and aggregates to break, except in systems with around 7.5 wt % GMO and 2.5 wt % PIBSA-PAM. The presence of micelles and adsorbed surfactants is found to be correlated with a low kinetic friction coefficient, and hence, there is an optimum composition range for friction reduction. This work highlights the importance of cooperative interactions between lubricant additives.
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Affiliation(s)
- Georgia Tsagkaropoulou
- School of Chemistry , University of Edinburgh , David Brewster Road , Edinburgh EH9 3FJ , Scotland
| | - Chris P Warrens
- Research and Technology Fuels and Lubricants , BP International Limited, Technology Centre , Whitchurch Hill, Pangbourne, Reading RG8 7QR , England
| | - Philip J Camp
- School of Chemistry , University of Edinburgh , David Brewster Road , Edinburgh EH9 3FJ , Scotland
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28
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Latorre CA, Ewen JP, Gattinoni C, Dini D. Simulating Surfactant–Iron Oxide Interfaces: From Density Functional Theory to Molecular Dynamics. J Phys Chem B 2019; 123:6870-6881. [DOI: 10.1021/acs.jpcb.9b02925] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
| | - James P. Ewen
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
| | - Chiara Gattinoni
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
- Department of Materials, ETH Zürich, Zürich 8092, Switzerland
| | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, U.K
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29
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30
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Chia CL, Alloway RM, Jephson I, Clarke SM, Filip SV, Siperstein FR, Avendaño C. Competitive Adsorption of a Multifunctional Amine and Phenol Surfactant with Ethanol on Hematite from Nonaqueous Solution. J Phys Chem B 2019; 123:1375-1383. [PMID: 30667225 DOI: 10.1021/acs.jpcb.8b09704] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Surfactants, which contain phenol and amine groups, are commonly used in industries to protect metallic surfaces, and their efficiency depends strongly on factors such as pressure and temperature, solvent properties, and the presence of other surfactants in the system. In this work, we present a molecular simulation study of the competitive adsorption between a multifunctional phenol and amine surfactant model and ethanol at the oil/solid interface formed between iso-octane and a model hematite (α-Fe2O3) slab. We show that the surfactant strongly adsorbs at the iso-octane/hematite interface in the absence of ethanol at moderate temperatures. As the concentration of ethanol is increased, the ethanol molecules compete effectively for the adsorption sites on the iron oxide surface. This competition drives the surfactant molecules to remain in the bulk solution, while ethanol forms ordered and strongly coordinated layers at the oil/solid interface, despite the well-known complete miscibility of ethanol in iso-octane in bulk under standard conditions. Potential of mean force calculations show that the free energy of adsorption of the surfactant is approximately two times larger than that for a single ethanol molecule, but the simulations also reveal that a single surfactant chain needs to displace up to five ethanol molecules to adsorb onto the surface. The end result is more favorable ethanol adsorption which agrees with the experimental analysis of similar oil/iron oxide systems also reported in this work.
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Affiliation(s)
- Chung-Lim Chia
- School of Chemical Engineering and Analytical Science , The University of Manchester , Oxford Road , Manchester M13 9PL , U.K
| | - Richard M Alloway
- Department of Chemistry and BP Institute , Cambridge University , Cambridge CB2 1EW , U.K
| | - Izaak Jephson
- Department of Chemistry and BP Institute , Cambridge University , Cambridge CB2 1EW , U.K
| | - Stuart M Clarke
- Department of Chemistry and BP Institute , Cambridge University , Cambridge CB2 1EW , U.K
| | - Sorin V Filip
- BP Formulated Products Technology, Research and Innovation, Technology Centre , Whitchurch Hill, Pangbourne, Berkshire RG8 7QR , U.K
| | - Flor R Siperstein
- School of Chemical Engineering and Analytical Science , The University of Manchester , Oxford Road , Manchester M13 9PL , U.K
| | - Carlos Avendaño
- School of Chemical Engineering and Analytical Science , The University of Manchester , Oxford Road , Manchester M13 9PL , U.K
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31
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Jaishankar A, Jusufi A, Vreeland JL, Deighton S, Pellettiere J, Schilowitz AM. Adsorption of Stearic Acid at the Iron Oxide/Oil Interface: Theory, Experiments, and Modeling. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:2033-2046. [PMID: 30624939 DOI: 10.1021/acs.langmuir.8b03132] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Improved friction performance is an important objective of equipment manufacturers for meeting improved energy efficiency demands. The addition of friction-reducing additives, or friction modifiers (FMs), to lubricants is a key part of the strategy. The performance of these additives is related to their surface activity and their ability to form adsorbed layers on the metal surface. However, the extent of surface coverage (mass per unit area) required for effective friction reduction is currently unknown. In this article, we show that full coverage is not necessary for significant friction reduction. We first highlight various features of surface adsorption that can influence the surface coverage, packing, and free energy of adsorption of organic FMs on iron oxide surfaces. Using stearic acid in heptane and hexadecane as model lubricant formulations, we employ a combination of experiments and molecular dynamics (MD) simulations to show how the dimerization of acid molecules in the bulk solvent and the crystallographic orientation of the surface modifies surface adsorption. In addition, we show that the solvent can strongly influence the adsorption kinetics, and MD simulations reveal that hexadecane tends to align on the surface, increasing the energy barrier for the adsorption of stearic acid to the surface. Furthermore, we present a combined approach using MD and molecular thermodynamic theory to calculate adsorption isotherms for stearic acid on iron oxide surfaces, which agrees well with experimental data obtained with a quartz crystal microbalance (QCM). Our results suggest that while the friction of systems lubricated with organic FMs decreases with increasing coverage, complete coverage of the surface is neither practically achievable nor necessary for effective friction reduction for the systems and conditions studied here.
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Affiliation(s)
- Aditya Jaishankar
- ExxonMobil Research and Engineering , 1545 Route 22 East , Annandale , New Jersey 08801 , United States
| | - Arben Jusufi
- ExxonMobil Research and Engineering , 1545 Route 22 East , Annandale , New Jersey 08801 , United States
| | - Jessica L Vreeland
- ExxonMobil Research and Engineering , 1545 Route 22 East , Annandale , New Jersey 08801 , United States
| | - Shane Deighton
- ExxonMobil Research and Engineering , 1545 Route 22 East , Annandale , New Jersey 08801 , United States
| | - Joseph Pellettiere
- ExxonMobil Research and Engineering , 1545 Route 22 East , Annandale , New Jersey 08801 , United States
| | - Alan M Schilowitz
- ExxonMobil Research and Engineering , 1545 Route 22 East , Annandale , New Jersey 08801 , United States
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32
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Mechano-chemical decomposition of organic friction modifiers with multiple reactive centres induces superlubricity of ta-C. Nat Commun 2019; 10:151. [PMID: 30635585 PMCID: PMC6484224 DOI: 10.1038/s41467-018-08042-8] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Accepted: 12/10/2018] [Indexed: 11/08/2022] Open
Abstract
Superlubricity of tetrahedral amorphous carbon (ta-C) coatings under boundary lubrication with organic friction modifiers is important for industrial applications, but the underlying mechanisms remain elusive. Here, combined experiments and simulations unveil a universal tribochemical mechanism leading to superlubricity of ta-C/ta-C tribopairs. Pin-on-disc sliding experiments show that ultra- and superlow friction with negligible wear can be achieved by lubrication with unsaturated fatty acids or glycerol, but not with saturated fatty acids and hydrocarbons. Atomistic simulations reveal that, due to the simultaneous presence of two reactive centers (carboxylic group and C=C double bond), unsaturated fatty acids can concurrently chemisorb on both ta-C surfaces and bridge the tribogap. Sliding-induced mechanical strain triggers a cascade of molecular fragmentation reactions releasing passivating hydroxyl, keto, epoxy, hydrogen and olefinic groups. Similarly, glycerol's three hydroxyl groups react simultaneously with both ta-C surfaces, causing the molecule's complete mechano-chemical fragmentation and formation of aromatic passivation layers with superlow friction.
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33
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Yamada S, Fujihara A, Yusa SI, Tanabe T, Kurihara K. Confined film structure and friction properties of triblock copolymer additives in oil-based lubrication. Polym J 2018. [DOI: 10.1038/s41428-018-0114-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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34
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Damera DP, Venuganti VVK, Nag A. Deciphering the Role of Bilayer of a Niosome towards Controlling the Entrapment and Release of Dyes. ChemistrySelect 2018. [DOI: 10.1002/slct.201800374] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
| | | | - Amit Nag
- Department of Chemistry; BITS Pilani Hyderabad Campus; Hyderabad-500078 India
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35
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Bradley-Shaw JL, Camp PJ, Dowding PJ, Lewtas K. Self-assembly and friction of glycerol monooleate and its hydrolysis products in bulk and confined non-aqueous solvents. Phys Chem Chem Phys 2018; 20:17648-17657. [DOI: 10.1039/c8cp01785a] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Molecular dynamics simulations are used to study the interplay between self-assembly, adsorption, and friction in solutions of amphiphilic additives dissolved in non-aqueous solvents.
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Affiliation(s)
| | - Philip J. Camp
- School of Chemistry
- University of Edinburgh
- Edinburgh EH9 3FJ
- UK
| | | | - Ken Lewtas
- School of Chemistry
- University of Edinburgh
- Edinburgh EH9 3FJ
- UK
- Lewtas Science & Technologies
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36
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Hirayama T, Kawamura R, Fujino K, Matsuoka T, Komiya H, Onishi H. Cross-Sectional Imaging of Boundary Lubrication Layer Formed by Fatty Acid by Means of Frequency-Modulation Atomic Force Microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:10492-10500. [PMID: 28960989 DOI: 10.1021/acs.langmuir.7b02528] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
To observe in situ the adsorption of fatty acid onto metal surfaces, cross-sectional images of the adsorption layer were acquired by frequency-modulation atomic force microscopy (FM-AFM). Hexadecane and palmitic acid were used as the base oil and typical fatty acid, respectively. A Cu-coated silicon wafer was prepared as the target substrate. The solvation structure formed by hexadecane molecules at the interface between the Cu substrate and the hexadecane was observed, and the layer pitch was found to be about 0.6 nm, which corresponds to the height of hexadecane molecules. This demonstrates that hexadecane molecules physically adsorbed onto the surface due to van der Waals forces with lying orientation because hexadecane is a nonpolar hydrocarbon. When hexadecane with palmitic acid was put on the Cu substrate instead of pure hexadecane, an adsorption layer of palmitic acid was observed at the interface. The layer pitch was about 2.5-2.8 nm, which matches the chain length of palmitic acid molecules well. This indicates that the original adsorption layer was monolayer or single bilayer in the local area. In addition, a cross-sectional image captured 1 h after observation started to reveal that the adsorbed additive layer gradually grew up to be thicker than about 20 nm due to an external stimulus, such as cantilever oscillation. This is the first report of in situ observation of an adsorbed layer by FM-AFM in the tribology field and demonstrates that FM-AFM is useful for clarifying the actual boundary lubrication mechanism.
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Affiliation(s)
- Tomoko Hirayama
- PRESTO, Japan Science and Technology Agency 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan
| | | | | | | | | | - Hiroshi Onishi
- Department of Chemistry, Kobe University 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan
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37
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Watanabe S, Nakano M, Miyake K, Sasaki S. Analysis of the Interfacial Molecular Behavior of a Lubrication Film of n-Dodecane Containing Stearic Acid under Lubricating Conditions by Sum Frequency Generation Spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:13649-13656. [PMID: 27966971 DOI: 10.1021/acs.langmuir.6b03954] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The molecular behavior of n-dodecane with added stearic acid at a friction interface was studied using sum frequency generation (SFG) spectroscopy and a tribometer. In the case of n-dodecane with stearic acid, under dynamic conditions, a strong peak from the symmetric stretching vibrational mode of methylene, which was not observed under static conditions, appears. However, this strong methylene peak was not observed in the case of only n-dodecane. The SFG spectrum in the C-H stretching mode region of n-dodecane-d26 with stearic acid in the dynamic condition was analogous to that in the static condition. These results indicate that the interfacial structure of stearic acid does not change under sliding condition. The n-dodecane on a stearic acid adsorption film is highly aligned. Moreover, from the sliding direction dependence of the SFG measurements, the molecular orientation of n-dodecane was deduced: n-dodecane on stearic acid adsorption films orient parallel to the sliding direction. These results have shown that the stearic acid adsorption film behaves as solid-like, which has also been mentioned in previous studies. Further, our results revealed a new function of stearic acid: the stearic acid adsorption film induces the formation of a well-defined n-dodecane interfacial structure and forces the n-dodecane molecules to orient along the sliding direction at the friction interface.
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Affiliation(s)
- Seiya Watanabe
- Tokyo University of Science , Department of Mechanical Engineering, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
| | - Miki Nakano
- Advanced Manufacturing Research Institute (AMRI), National Institute of Advanced Industrial Science and Technology (AIST) , 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan
| | - Koji Miyake
- Advanced Manufacturing Research Institute (AMRI), National Institute of Advanced Industrial Science and Technology (AIST) , 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan
| | - Shinya Sasaki
- Tokyo University of Science , Department of Mechanical Engineering, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
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38
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Hernández Velázquez JD, Barroso-Flores J, Gama Goicochea A. Ab Initio Modeling Of Friction Reducing Agents Shows Quantum Mechanical Interactions Can Have Macroscopic Manifestation. J Phys Chem A 2016; 120:9244-9248. [PMID: 27800689 DOI: 10.1021/acs.jpca.6b07890] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two of the most commonly encountered friction-reducing agents used in plastic sheet production are the amides known as erucamide and behenamide, which despite being almost identical chemically, lead to markedly different values of the friction coefficient. To understand the origin of this contrasting behavior, in this work we model brushes made of these two types of linear-chain molecules using quantum mechanical numerical simulations under the density functional theory at the B97D/6-31G(d,p) level of theory. Four chains of erucamide and behenamide were linked to a 2 × 10 zigzag graphene sheet and optimized both in vacuum and in continuous solvent using the SMD implicit solvation model. We find that erucamide chains tend to remain closer together through π-π stacking interactions arising from the double bonds located at C13-C14, a feature behenamide lacks, and thus a more spread configuration is obtained with the latter. It is argued that this arrangement of the erucamide chains is responsible for the lower friction coefficient of erucamide brushes, compared with behenamide brushes, which is a macroscopic consequence of cooperative quantum mechanical interactions. While only quantum level interactions are modeled here, we show that behenamide chains are more spread out in the brush than erucamide chains as a consequence of those interactions. The spread-out configuration allows more solvent particles to penetrate the brush, leading in turn to more friction, in agreement with macroscopic measurements and mesoscale simulations of the friction coefficient reported in the literature.
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Affiliation(s)
- J D Hernández Velázquez
- Centro de Investigación en Ciencias Físico-Matemáticas, Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León , San Nicolás de los Garza 66450, Nuevo León, Mexico
| | - J Barroso-Flores
- Centro Conjunto de Investigación en Química Sustentable, UAEM-UNAM , Carretera Toluca-Atlacomulco Km 14.5, Unidad San Cayetano-Toluca 50200, Estado de México, Mexico
| | - A Gama Goicochea
- División de Ingeniería Química y Bioquímica, Tecnológico de Estudios Superiores de Ecatepec , Av. Tecnológico s/n, Ecatepec 55210, Estado de México, Mexico
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39
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Bradley-Shaw JL, Camp PJ, Dowding PJ, Lewtas K. Molecular Dynamics Simulations of Glycerol Monooleate Confined between Mica Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:7707-7718. [PMID: 27429247 DOI: 10.1021/acs.langmuir.6b00091] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The structure and frictional properties of glycerol monooleate (GMO) in organic solvents, with and without water impurity, confined and sheared between two mica surfaces are examined using molecular dynamics simulations. The structure of the fluid is characterized in various ways, and the differences between systems with nonaggregated GMO and with preformed GMO reverse micelles are examined. Preformed reverse micelles are metastable under static conditions in all systems. In n-heptane under shear conditions, with or without water, preformed GMO reverse micelles remain intact and adsorb onto one surface or another, becoming surface micelles. In dry toluene, preformed reverse micelles break apart under shear, while in the presence of water, the reverse micelles survive and become surface micelles. In all systems under static and shear conditions, nonaggregated GMO adsorbs onto both surfaces with roughly equal probability. Added water is strongly associated with the GMO, irrespective of shear or the form of the added GMO. In all cases, with increasing shear rate, the GMO molecules flatten on the surface, and the kinetic friction coefficient increases. Under low-shear conditions, the friction is insensitive to the form of the GMO added, whereas the presence of water is found to lead to a small reduction in friction. Under high-shear conditions, the presence of reverse micelles leads to a significant reduction in friction, whereas the presence of water increases the friction in n-heptane and decreases the friction in toluene.
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Affiliation(s)
- Joshua L Bradley-Shaw
- School of Chemistry, University of Edinburgh , David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Philip J Camp
- School of Chemistry, University of Edinburgh , David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Peter J Dowding
- Infineum UK Ltd., P.O. Box 1, Milton Hill, Abingdon OX13 6BB, U.K
| | - Ken Lewtas
- School of Chemistry, University of Edinburgh , David Brewster Road, Edinburgh EH9 3FJ, Scotland
- Lewtas Science & Technologies, 246 Banbury Road, Oxford OX2 7DY, U.K
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40
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Ewen JP, Gattinoni C, Thakkar FM, Morgan N, Spikes HA, Dini D. A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants. MATERIALS 2016; 9:ma9080651. [PMID: 28773773 PMCID: PMC5509262 DOI: 10.3390/ma9080651] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 07/20/2016] [Accepted: 07/28/2016] [Indexed: 01/26/2023]
Abstract
For the successful development and application of lubricants, a full understanding of their complex nanoscale behavior under a wide range of external conditions is required, but this is difficult to obtain experimentally. Nonequilibrium molecular dynamics (NEMD) simulations can be used to yield unique insights into the atomic-scale structure and friction of lubricants and additives; however, the accuracy of the results depend on the chosen force-field. In this study, we demonstrate that the use of an accurate, all-atom force-field is critical in order to; (i) accurately predict important properties of long-chain, linear molecules; and (ii) reproduce experimental friction behavior of multi-component tribological systems. In particular, we focus on n-hexadecane, an important model lubricant with a wide range of industrial applications. Moreover, simulating conditions common in tribological systems, i.e., high temperatures and pressures (HTHP), allows the limits of the selected force-fields to be tested. In the first section, a large number of united-atom and all-atom force-fields are benchmarked in terms of their density and viscosity prediction accuracy of n-hexadecane using equilibrium molecular dynamics (EMD) simulations at ambient and HTHP conditions. Whilst united-atom force-fields accurately reproduce experimental density, the viscosity is significantly under-predicted compared to all-atom force-fields and experiments. Moreover, some all-atom force-fields yield elevated melting points, leading to significant overestimation of both the density and viscosity. In the second section, the most accurate united-atom and all-atom force-field are compared in confined NEMD simulations which probe the structure and friction of stearic acid adsorbed on iron oxide and separated by a thin layer of n-hexadecane. The united-atom force-field provides an accurate representation of the structure of the confined stearic acid film; however, friction coefficients are consistently under-predicted and the friction-coverage and friction-velocity behavior deviates from that observed using all-atom force-fields and experimentally. This has important implications regarding force-field selection for NEMD simulations of systems containing long-chain, linear molecules; specifically, it is recommended that accurate all-atom potentials, such as L-OPLS-AA, are employed.
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Affiliation(s)
- James P Ewen
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK.
| | - Chiara Gattinoni
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK.
| | - Foram M Thakkar
- Shell India Markets Private Limited, 8B RMZ Centennial Building, Kundanahalli Main Road, Bangalore 560048, India.
| | - Neal Morgan
- Shell Global Solutions UK Ltd., Brabazon House, Manchester M22 0RR, UK.
| | - Hugh A Spikes
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK.
| | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK.
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41
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Singh MK, Ilg P, Espinosa-Marzal RM, Spencer ND, Kröger M. Influence of Chain Stiffness, Grafting Density and Normal Load on the Tribological and Structural Behavior of Polymer Brushes: A Nonequilibrium-Molecular-Dynamics Study. Polymers (Basel) 2016; 8:E254. [PMID: 30974530 PMCID: PMC6431904 DOI: 10.3390/polym8070254] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 06/24/2016] [Accepted: 07/01/2016] [Indexed: 12/16/2022] Open
Abstract
We have performed coarse-grained molecular-dynamics simulations on both flexible and semiflexible multi-bead-spring model polymer brushes in the presence of explicit solvent particles, to explore their tribological and structural behaviors. The effect of stiffness and tethering density on equilibrium-brush height is seen to be well reproduced within a Flory-type theory. After discussing the equilibrium behavior of the model brushes, we first study the shearing behavior of flexible chains at different grafting densities covering brush and mushroom regimes. Next, we focus on the effect of chain stiffness on the tribological behavior of polymer brushes. The tribological properties are interpreted by means of the simultaneously recorded density profiles. We find that the friction coefficient decreases with increasing persistence length, both in velocity and separation-dependency studies, over the stiffness range explored in this work.
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Affiliation(s)
- Manjesh K Singh
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.
| | - Patrick Ilg
- School of Mathematical and Physical Sciences, University of Reading, Reading RG6 6AX, UK.
| | - Rosa M Espinosa-Marzal
- Laboratory for Smart Interfaces in Environmental Nanotechnology, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, IL 61801, USA.
| | - Nicholas D Spencer
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.
| | - Martin Kröger
- Polymer Physics, Department of Materials, ETH Zurich, CH⁻8093 Zurich, Switzerland.
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42
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Ewen JP, Gattinoni C, Morgan N, Spikes HA, Dini D. Nonequilibrium Molecular Dynamics Simulations of Organic Friction Modifiers Adsorbed on Iron Oxide Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:4450-4463. [PMID: 27064962 DOI: 10.1021/acs.langmuir.6b00586] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
For the successful development and application of lubricants, a full understanding of the nanoscale behavior of complex tribological systems is required, but this is difficult to obtain experimentally. In this study, we use nonequilibrium molecular dynamics (NEMD) simulations to examine the atomistic structure and friction properties of commercially relevant organic friction modifier (OFM) monolayers adsorbed on iron oxide surfaces and lubricated by a thin, separating layer of hexadecane. Specifically, acid, amide, and glyceride OFMs, with saturated and Z-unsaturated hydrocarbon tail groups, are simulated at various surface coverages and sliding velocities. At low and medium coverage, the OFMs form liquidlike and amorphous monolayers, respectively, which are significantly interdigitated with the hexadecane lubricant, resulting in relatively high friction coefficients. At high coverage, solidlike monolayers are formed for all of the OFMs, which, during sliding, results in slip planes between well-defined OFM and hexadecane layers, yielding a marked reduction in the friction coefficient. When present at equal surface coverage, OFMs with saturated and Z-unsaturated tail groups are found to yield similar structure and friction behavior. OFMs with glyceride head groups yield significantly lower friction coefficients than amide and particularly carboxylic acid head groups. For all of the OFMs and coverages simulated, the friction coefficient is found to increase linearly with the logarithm of sliding velocity; however, the gradient of this increase depends on the coverage. The structure and friction details obtained from these simulations agree well with experimental results and also shed light on the relative tribological performance of these OFMs through nanoscale structural variations. This has important implications in terms of the applicability of NEMD to aid the development of new formulations to control friction.
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Affiliation(s)
- James P Ewen
- Department of Mechanical Engineering, Imperial College London , London SW7 2AZ, England
| | - Chiara Gattinoni
- Department of Mechanical Engineering, Imperial College London , London SW7 2AZ, England
| | - Neal Morgan
- Shell Global Solutions UK Ltd, Manchester M22 0RR, Lancashire, England
| | - Hugh A Spikes
- Department of Mechanical Engineering, Imperial College London , London SW7 2AZ, England
| | - Daniele Dini
- Department of Mechanical Engineering, Imperial College London , London SW7 2AZ, England
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43
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Wood MH, Casford MT, Steitz R, Zarbakhsh A, Welbourn RJL, Clarke SM. Comparative Adsorption of Saturated and Unsaturated Fatty Acids at the Iron Oxide/Oil Interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:534-540. [PMID: 26707597 DOI: 10.1021/acs.langmuir.5b04435] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A detailed comparison of the adsorption behavior of long straight chain saturated and unsaturated fatty acids at the iron oxide/oil interface has been considered using a combination of surface study techniques. Both depletion isotherms and polarized neutron reflectometry (PNR) show that the extent of adsorption decreases as the number of double bonds in the alkyl chains increases. Sum frequency generation spectroscopic measurements demonstrate that there is also an increase in chain disorder within the adsorbed layer as the unsaturation increases. However, for the unsaturated analogues, a decrease in peak intensity is seen for the double bond peak upon heating, which is thought to arise from isomerization in the surface-bound layer. The PNR study of oleic acid adsorption indicates chemisorbed monolayer adsorption, with a further diffuse reversible adsorbed layer formed at higher concentrations.
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Affiliation(s)
- Mary H Wood
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
| | - M T Casford
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
| | - R Steitz
- Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, Berlin 14109, Germany
| | - A Zarbakhsh
- School of Biological and Chemical Science, Queen Mary, University of London , Joseph Priestly Building, Mile End Road, London WC1E 7HU, United Kingdom
| | - R J L Welbourn
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
| | - Stuart M Clarke
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
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Yamada S, Fujihara A, Yusa SI, Tanabe T, Kurihara K. Low-Friction Adsorbed Layers of a Triblock Copolymer Additive in Oil-Based Lubrication. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:12140-12147. [PMID: 26479685 DOI: 10.1021/acs.langmuir.5b03620] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The tribological properties of the dilute solution of an ABA triblock copolymer, poly(11-acrylamidoundecanoic acid)-block-poly(stearyl methacrylate)-block-poly(11-acrylamidoundecanoic acid (A5S992A5), in poly(α-olefin) (PAO) confined between mica surfaces were investigated using the surface forces apparatus (SFA). Friction force was measured as a function of applied load and sliding velocity, and the film thickness and contact geometry during sliding were analyzed using the fringes of equal chromatic order (FECO) in the SFA. The results were contrasted with those of confined PAO films; the effects of the addition of A5S992A5 on the tribological properties were discussed. The thickness of the A5S992A5/PAO system varied with time after surface preparation and with repetitive sliding motions. The thickness was within the range from 40 to 70 nm 1 day after preparation (the Day1 film), and was about 20 nm on the following day (the Day2 film). The thickness of the confined PAO film was thinner than 1.4 nm, indicating that the A5S992A5/PAO system formed thick adsorbed layers on mica surfaces. The friction coefficient was about 0.03 to 0.04 for the Day1 film and well below 0.01 for the Day2 film, which were 1 or 2 orders of magnitude lower than the values for the confined PAO films. The time dependent changes of the adsorbed layer thickness and friction properties should be caused by the relatively low solubility of A5S992A5 in PAO. The detailed analysis of the contact geometry and friction behaviors implies that the particularly low friction of the Day2 film originates from the following factors: (i) shrinkage of the A5S992A5 molecules (mainly the poly(stearyl methacrylate) blocks) that leads to a viscoelastic properties of the adsorbed layers; and (ii) the intervening PAO layer between the adsorbed polymer layers that constitutes a high-fluidity sliding interface. Our results suggest that the block copolymer having relatively low solubility in a lubricant base oil is effective at forming low-friction adsorbed layers in oil-based lubrication.
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Affiliation(s)
- Shinji Yamada
- New Industry Creation Hatchery Center, Tohoku University , 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
| | - Ami Fujihara
- Graduate School of Engineering, University of Hyogo , 2167 Shosha, Himeji, Hyogo 671-2280, Japan
| | - Shin-ichi Yusa
- Graduate School of Engineering, University of Hyogo , 2167 Shosha, Himeji, Hyogo 671-2280, Japan
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Doig M, Camp PJ. The structures of hexadecylamine films adsorbed on iron-oxide surfaces in dodecane and hexadecane. Phys Chem Chem Phys 2015; 17:5248-55. [DOI: 10.1039/c4cp05837b] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The structure and friction of hexadecylamine surfactant films on iron oxide in alkanes are studied using large-scale molecular-dynamics simulations.
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Affiliation(s)
- Michael Doig
- School of Chemistry
- University of Edinburgh
- Edinburgh
- UK
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