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Hsu CC, Peng L, Hsia FC, Weber B, Bonn D, Brouwer AM. Molecular Probing of the Stress Activation Volume in Vapor Phase Lubricated Friction. ACS APPLIED MATERIALS & INTERFACES 2023; 15:12603-12608. [PMID: 36827622 PMCID: PMC9999409 DOI: 10.1021/acsami.3c00789] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 02/16/2023] [Indexed: 06/18/2023]
Abstract
When two solid objects slide over each other, friction results from the interactions between the asperities of the (invariably rough) surfaces. Lubrication happens when viscous lubricants separate the two surfaces and carry the load such that solid-on-solid contacts are avoided. Yet, even small amounts of low-viscosity lubricants can still significantly lower friction through a process called boundary lubrication. Understanding the origin of the boundary lubricating effect is hampered by challenges in measuring the interfacial properties of lubricants directly between the two surfaces. Here, we use rigidochromic fluorescent probe molecules to measure precisely what happens on a molecular scale during vapor-phase boundary lubrication of a polymer bead-on-glass interface. The probe molecules have a longer fluorescence lifetime in a confined environment, which allows one to measure the area of real contact between rough surfaces and infer the shear stress at the lubricated interfaces. The latter is shown to be proportional to the inverse of the local interfacial free volume determined using the measured fluorescence lifetime. The free volume can then be used in an Eyring-type model as the stress activation volume, allowing to collapse the data of stress as a function of sliding velocity and partial pressure of the vapor phase lubricant. This shows directly that as more boundary lubricant is applied, larger clusters of lubricant molecules become involved in the shear process thereby lowering the friction.
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Affiliation(s)
- Chao-Chun Hsu
- van
’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Liang Peng
- van
der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Feng-Chun Hsia
- van
der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
- Advanced
Research Center for Nanolithography, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Bart Weber
- van
der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
- Advanced
Research Center for Nanolithography, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Daniel Bonn
- van
der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Albert M. Brouwer
- van
’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
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Luo Y, Jiang S, Xiao Q, Chen C, Li B. Highly reusable and superhydrophobic spongy graphene aerogels for efficient oil/water separation. Sci Rep 2017; 7:7162. [PMID: 28769065 PMCID: PMC5540914 DOI: 10.1038/s41598-017-07583-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Accepted: 06/27/2017] [Indexed: 02/07/2023] Open
Abstract
Graphene aerogels (GAs) are three-dimensional (3D) graphene sponges with unique wettability and have demonstrated the potential for reducing contamination from oil spills and chemical accidents. Herein, we report new polyurethane (PU) sponge-reinforced GAs with low surface energy, high sorption capacity and excellent recyclability for use as efficient oil sorbents. Spongy graphene aerogels (SGAs) with a hierarchical porous morphology were produced by simply freeze-casting reduced graphene oxide (rGO) to form compacted macroscale sponges. This novel micro-structure benefits from the advantages of embedded graphene and presents reversible large-strain deformation (90%), high compressive strength (63 kpa) and viscoelastic stability. These superior properties, in addition to super-hydrophobicity, endow the aerogels with excellent recyclability without deteriorating the oil absorption performance. Furthermore, SGA has selective and high-volume absorbability (>100%) and can efficiently separate oil from water under continuous pumping action. The excellent absorption performance and robust mechanical properties make this graphene material promising for the large-scale recovery of spilled oil.
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Affiliation(s)
- Yuanzheng Luo
- Key Laboratory of Electronic information functional material of Ministry of Education, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Shenlin Jiang
- Key Laboratory of Electronic information functional material of Ministry of Education, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Qi Xiao
- Key Laboratory of Electronic information functional material of Ministry of Education, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Chuanliang Chen
- Key Laboratory of Electronic information functional material of Ministry of Education, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Buyin Li
- Key Laboratory of Electronic information functional material of Ministry of Education, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China.
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Godet C. Dielectric relaxation properties of carboxylic acid-terminated n-alkyl monolayers tethered to Si(1 1 1): dynamics of dipoles and gauche defects. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:094012. [PMID: 26872003 DOI: 10.1088/0953-8984/28/9/094012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Molecular-level insights into the organization and dynamics of n-alkyl monolayers covalently bonded to Si(1 1 1) were gained from admittance measurements of dipolar relaxation in rectifying Hg|| HOOC-C10H(25-n) Si junctions performed as a function of applied voltage and temperature. A collective behavior of dipole dynamics is inferred from the non-Debye asymmetric relaxation peak shape and strong coupling of the dipole relaxation path with some bending vibrations of the n-alkyl OML (multi-excitation entropy model). A variety of relaxation mechanisms is observed in the frequency range (0.1 Hz-10 MHz) with different dependence of relaxation frequency and dipolar strength on measurement temperature and applied voltage. Their microscopic origin is discussed by comparing the activation energy of relaxation frequency with previous molecular mechanics calculations of saddle point energy barriers for structural defects such as gauche conformations or chain kinks in n-alkanes assemblies. Gauche conformations organized in pairs (kinks) have vanishing relaxation strength below an order-disorder transition temperature T(D) = 175 K and their probability strongly increases with applied reverse voltage, above T(D). The presence of hydrogen bonds between terminal carboxylic acid functionalities is inferred from a comparison with a similar junction bearing a low density of carboxylic acid end groups. This temperature-dependent hydrogen-bond network provides some additional stiffness against external electrostatic stress, as deduced from the rather weak sensitivity of relaxation frequencies to applied bias voltage.
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Affiliation(s)
- C Godet
- Institut de Physique de Rennes, UMR 6251 CNRS-Université de Rennes 1, 35042 Rennes Cedex, France
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Delorme N, Chebil MS, Vignaud G, Le Houerou V, Bardeau JF, Busselez R, Gibaud A, Grohens Y. Experimental evidence of ultrathin polymer film stratification by AFM force spectroscopy. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2015; 38:56. [PMID: 26087914 DOI: 10.1140/epje/i2015-15056-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 03/25/2015] [Accepted: 05/11/2015] [Indexed: 06/04/2023]
Abstract
By performing Atomic Force Microscopy measurements of pull-off force as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) films. Thermal transitions induce modifications in the surface energy, roughness and surface modulus that are clearly detected by AFM and related to PS chain relaxation mechanisms. We demonstrated the existence of three transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. The thickness of this region is estimated to be above 7nm. The detection of a transition only present for film thicker than the gyration radius Rg is linked to the dynamics of polymer chains in a bulk conformation (i.e. not in contact with the free interface). We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in terms of relaxation behavior.
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Affiliation(s)
- Nicolas Delorme
- Institut des Molécules et Matériaux du Mans (IMMM) - UMR CNRS 6283, Université du Maine, Avenue Olivier Messiaen, 72000, Le Mans, France.
| | - Mohamed Souheib Chebil
- Institut des Molécules et Matériaux du Mans (IMMM) - UMR CNRS 6283, Université du Maine, Avenue Olivier Messiaen, 72000, Le Mans, France
| | - Guillaume Vignaud
- Laboratoire d'Ingénierie des Matériaux de Bretagne (LIMATB), Université de Bretagne Sud, Rue Saint Maudé, 56321, Lorient, France
| | - Vincent Le Houerou
- Institut Charles Sadron (ICS), Université de Strasbourg, 67034, Strasbourg, France
| | - Jean-François Bardeau
- Institut des Molécules et Matériaux du Mans (IMMM) - UMR CNRS 6283, Université du Maine, Avenue Olivier Messiaen, 72000, Le Mans, France
| | - Rémi Busselez
- Institut des Molécules et Matériaux du Mans (IMMM) - UMR CNRS 6283, Université du Maine, Avenue Olivier Messiaen, 72000, Le Mans, France
| | - Alain Gibaud
- Institut des Molécules et Matériaux du Mans (IMMM) - UMR CNRS 6283, Université du Maine, Avenue Olivier Messiaen, 72000, Le Mans, France
| | - Yves Grohens
- Laboratoire d'Ingénierie des Matériaux de Bretagne (LIMATB), Université de Bretagne Sud, Rue Saint Maudé, 56321, Lorient, France
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Godet C. Entropy effects in the collective dynamic behavior of alkyl monolayers tethered to Si(111). BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2015; 6:583-594. [PMID: 25821699 PMCID: PMC4362335 DOI: 10.3762/bjnano.6.60] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 02/05/2015] [Indexed: 06/04/2023]
Abstract
Dynamic properties of n-alkyl monolayers covalently bonded to Si(111) were studied by broadband admittance spectroscopy as a function of the temperature and the applied voltage using rectifying Hg/C12H25/n-type Si junctions. Partial substitution of methyl end groups by polar (carboxylic acid) moieties was used to enhance the chain end relaxation response. Two thermally activated dissipation mechanisms (B1 and B2, with f B1 < f B2) are evidenced for all reverse bias values. The strong decrease of both relaxation frequencies with increasing reverse dc bias reveals increasing motional constraints, attributed to electrostatic pressure applied to the densely-packed nanometer-thick monolayer. Spectral decomposition of the frequency response shows a power-law dependence of their activation energies on |V DC|. A large reverse bias reversibly increases the B2 response attributed to the distribution of gauche defects, in contrast with the constant strength of the acid dipole loss (B1). A trans-gauche isomerization energy of 50 meV is derived from the temperature dependence of the B2 dipolar strength. For both dissipation mechanisms, the observed linear correlation between activation energy and logarithm of pre-exponential factor is consistent with a multi-excitation entropy model, in which the molecular reorientation path is strongly coupled with a large number of low energy excitations (here the n-alkyl bending vibrational mode) collected from the thermal bath. This collective dynamic behavior of alkyl chains tethered to Si is also confirmed by the asymmetric relaxation peak shape related to many-body interactions in complex systems.
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Affiliation(s)
- Christian Godet
- Institut de Physique de Rennes, UMR 6251 CNRS - Université de Rennes 1, 35042 Rennes Cedex, France
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Wu Y, Yi N, Huang L, Zhang T, Fang S, Chang H, Li N, Oh J, Lee JA, Kozlov M, Chipara AC, Terrones H, Xiao P, Long G, Huang Y, Zhang F, Zhang L, Lepró X, Haines C, Lima MD, Lopez NP, Rajukumar LP, Elias AL, Feng S, Kim SJ, Narayanan NT, Ajayan PM, Terrones M, Aliev A, Chu P, Zhang Z, Baughman RH, Chen Y. Three-dimensionally bonded spongy graphene material with super compressive elasticity and near-zero Poisson’s ratio. Nat Commun 2015; 6:6141. [DOI: 10.1038/ncomms7141] [Citation(s) in RCA: 413] [Impact Index Per Article: 45.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 12/16/2014] [Indexed: 12/21/2022] Open
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Solar M, Meyer H, Gauthier C. Analysis of local properties during a scratch test on a polymeric surface using molecular dynamics simulations. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2013; 36:29. [PMID: 23526081 DOI: 10.1140/epje/i2013-13029-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Accepted: 02/21/2013] [Indexed: 06/02/2023]
Abstract
This work demonstrates a possible route to connect a particle (chain) based understanding with continuum mechanical questions about contact mechanics. The bond orientation, chain conformation and stress field of a polymer film were analyzed during scratch tests (tangential contact) using a molecular dynamics (MD) simulation approach. Scratch tests with a conical tip at constant scratching velocity were simulated on linear amorphous polymer surfaces at various temperatures and roughnesses of the tip and for various interactions between the tip and the particles of the polymer chains. The second Legendre polynomial (computed for small domains around the tip) gave the bond orientation inside the polymer film during sliding of the tip. The gyration tensor (layer-resolved in the direction of the polymer film thickness) provided information about the conformation of the polymer chains. These results allowed us to argue in favor of Briscoe's hypothesis (thin film sheared vs. "bulk" compressive behavior) concerning the friction properties of the polymer surfaces. Finally, the first stress measurements of the virial stress tensor (in sub-boxes placed in the MD cell) revealed a complex combination between compressive hydrostatic pressure and shear stress, which may be interpreted as a complex sheared domain at the interface.
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Affiliation(s)
- M Solar
- Institut Charles Sadron (UPR22-CNRS), University of Strasbourg, 23 rue du Loess, BP 84047, F-67034, Strasbourg, France.
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Knorr DB, Benight SJ, Krajina B, Zhang C, Dalton LR, Overney RM. Nanoscale Phase Analysis of Molecular Cooperativity and Thermal Transitions in Dendritic Nonlinear Optical Glasses. J Phys Chem B 2012; 116:13793-805. [DOI: 10.1021/jp307370y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Daniel B. Knorr
- Weapons and Materials Research
Directorate, United States Army Research Laboratory, Aberdeen Proving Ground, Maryland 21009, United States
| | | | | | - Cheng Zhang
- Department of Chemistry and
Biochemistry, South Dakota State University, Brookings, South Dakota 57007-0896, United States
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