1
|
Perrino C, Lee S, Spencer ND. Quantitative Comparison of the Hydration Capacity of Surface-Bound Dextran and Polyethylene Glycol. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:14130-14140. [PMID: 38922294 PMCID: PMC11238585 DOI: 10.1021/acs.langmuir.4c01582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2024] [Revised: 06/12/2024] [Accepted: 06/13/2024] [Indexed: 06/27/2024]
Abstract
We have quantified and compared the hydration capacity (i.e., capability to incorporate water molecules) of the two surface-bound hydrophilic polymer chains, dextran (dex) and poly(ethylene glycol) (PEG), in the form of poly(l-lysine)-graft-dextran (PLL-g-dex) and poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), respectively. The copolymers were attached to a negatively charged silica-titania surface through the electrostatic interaction between the PLL backbone and the surface in neutral aqueous media. While the molecular weights of PLL and PEG were fixed, that of dex and the grafting density of PEG or dex on the PLL were varied. The hydration capacity of the polymer chains was quantified through the combined experimental approach of optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance with dissipation monitoring (QCM-D) to yield a value for areal solvation (Ψ), i.e., mass of associated solvent molecules within the polymer chains per unit substrate area. For the two series of copolymers with comparable stretched chain lengths of hydrophilic polymers, namely, PLL(20)-g-PEG(5) and PLL(20)-g-dex(10), the Ψ values gradually increased as the initial grafting density on the PLL backbone increased or as g decreased. However, the rate of increase in Ψ was higher for PEG than dextran chains, which was attributed to higher stiffness of the dextran chains. More importantly, the number of water molecules per hydrophilic group was clearly higher for PEG chains. Given that the -CH2CH2O- units that make up the PEG chains form a cage-like structure with 2-3 water molecules, these "strongly bound" water molecules can account for the slightly more favorable behavior of PEG compared to dextran in both aqueous lubrication and antifouling behavior of the copolymers.
Collapse
Affiliation(s)
- Chiara Perrino
- Laboratory
for Surface Science and Technology, Department of Materials, Vladimir-Prelog-Weg
5, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Seunghwan Lee
- Laboratory
for Surface Science and Technology, Department of Materials, Vladimir-Prelog-Weg
5, ETH Zurich, CH-8093 Zurich, Switzerland
- Institute
of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT Leeds, U.K.
| | - Nicholas D. Spencer
- Laboratory
for Surface Science and Technology, Department of Materials, Vladimir-Prelog-Weg
5, ETH Zurich, CH-8093 Zurich, Switzerland
| |
Collapse
|
2
|
Kumar A, Kumar V, Joshi YM, Singh MK. Tribological and Rheological Study of Thixotropic Gels of 2D Nanoparticles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:7310-7327. [PMID: 38426447 DOI: 10.1021/acs.langmuir.3c03220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/02/2024]
Abstract
A thixotropic colloidal gel constituting an aqueous dispersion of synthetic clay Laponite with varying concentrations of salt has been studied for its rheological and tribological performance as a lubricant. We observed that the incorporation of NaCl induces notable enhancements in the colloidal gel's relaxation time, elastic modulus, and yield stress. Although an increase in NaCl concentration decreases the material's relaxation time dependence on waiting time (tw), overall, the strength of its thixotropic character has been observed to increase with an increase in salt concentration. The analysis of friction and wear indicated that the utilization of a thixotropic colloidal gel of Laponite with a higher concentration of NaCl resulted in progressively greater reductions in both the coefficient of friction and specific wear rates under various load-speed conditions. Severe abrasive wear on disc surface under dry test, gradually mitigated upon the introduction of these lubricants. Two simultaneous lubricating mechanisms, first, the smooth sliding of the friction pair, facilitated by the alignment of Laponite particles in the direction of shear forces, and second, the stable structure of Laponite, coupled with the addition of NaCl, enabling continuous replenishment of the wear track with lubricant, are attributed to lubrication effectiveness.
Collapse
Affiliation(s)
- Arun Kumar
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| | - Vivek Kumar
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| | - Yogesh M Joshi
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| | - Manjesh Kumar Singh
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| |
Collapse
|
3
|
Zheng J, Jo S, Chen J, Das B, Juhasz L, Cabral H, Sugihara K. Dual Nanofriction Force Microscopy/Fluorescence Microscopy Imaging Reveals the Enhanced Force Sensitivity of Polydiacetylene by pH and NaCl. Anal Chem 2023. [PMID: 37465896 DOI: 10.1021/acs.analchem.3c01433] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/20/2023]
Abstract
Polydiacetylene (PDA) is a popular mechanochromic material often used in biosensing. The effect of its headgroup-headgroup interactions on thermochromism such as pH or salt concentration dependency has been extensively studied before; however, their effect on mechanochromism at the nanoscale is left unstudied. In this work, nanofriction force microscopy and fluorescence microscopy were combined to study the effect of pH and ionic strength on the polydiacetylene (PDA) force sensitivity at the nanoscale. We found that the increase in pH from 5.7 to 8.2 caused an 8-fold enhancement in force sensitivity. The elevation of NaCl concentration from 10 to 200 mM also made the PDA 5 times more force-sensitive. These results suggest that the PDA force sensitivity at the nanoscale can be conveniently enhanced by "pre-stimulation" with pH or ionic strength.
Collapse
Affiliation(s)
- Jianlu Zheng
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8505, Japan
| | - Seiko Jo
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8505, Japan
| | - Jiali Chen
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8505, Japan
| | - Bratati Das
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8505, Japan
| | - Levente Juhasz
- Department of Physical Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland
| | - Horacio Cabral
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Kaori Sugihara
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8505, Japan
| |
Collapse
|
4
|
Polymer brushes for friction control: Contributions of molecular simulations. Biointerphases 2023; 18:010801. [PMID: 36653299 DOI: 10.1116/6.0002310] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
When polymer chains are grafted to solid surfaces at sufficiently high density, they form brushes that can modify the surface properties. In particular, polymer brushes are increasingly being used to reduce friction in water-lubricated systems close to the very low levels found in natural systems, such as synovial joints. New types of polymer brush are continually being developed to improve with lower friction and adhesion, as well as higher load-bearing capacities. To complement experimental studies, molecular simulations are increasingly being used to help to understand how polymer brushes reduce friction. In this paper, we review how molecular simulations of polymer brush friction have progressed from very simple coarse-grained models toward more detailed models that can capture the effects of brush topology and chemistry as well as electrostatic interactions for polyelectrolyte brushes. We pay particular attention to studies that have attempted to match experimental friction data of polymer brush bilayers to results obtained using molecular simulations. We also critically look at the remaining challenges and key limitations to overcome and propose future modifications that could potentially improve agreement with experimental studies, thus enabling molecular simulations to be used predictively to modify the brush structure for optimal friction reduction.
Collapse
|
5
|
Kodakkadan YNV, Maslen C, Cigler P, Štěpánek F, Rehor I. Friction-directed self-assembly of Janus lithographic microgels into anisotropic 2D structures. J Mater Chem B 2021; 9:4718-4725. [PMID: 34076033 DOI: 10.1039/d1tb00572c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
We present a method for creating ordered 2D structures with material anisotropy from self-assembling micro-sized hydrogel particles (microgels). Microgel platelets of polygonal shapes (hexagon, square, and rhombus), obtained by a continuous scalable lithographic process, are suspended in an aqueous environment and sediment on an inclined plane. As a consequence of gravitational pull, they slide over the plane. Each half of the microgel is composed of a different type of hydrogel [poly(N-isopropylacrylamide) (PNIPAM), and poly(ethylene glycol) diacrylate (PEGDA), respectively] which exhibit different frictional coefficients when sheared over a substrate. Hence the microgels self-orientate as they slide, and the side with the lower frictional coefficient positions in the direction of sliding. The self-oriented microgels concentrate at the bottom of the tilted plane. Here they form densely packed structures with translational as well as orientational order.
Collapse
Affiliation(s)
| | - Charlie Maslen
- University of Chemistry and Technology Prague, Faculty of Chemical Engineering, Technicka 5, 166 28 Prague 6, Czech Republic.
| | - Petr Cigler
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nam. 2, 160 00, Prague, Czech Republic
| | - František Štěpánek
- University of Chemistry and Technology Prague, Faculty of Chemical Engineering, Technicka 5, 166 28 Prague 6, Czech Republic.
| | - Ivan Rehor
- University of Chemistry and Technology Prague, Faculty of Chemical Engineering, Technicka 5, 166 28 Prague 6, Czech Republic. and Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nam. 2, 160 00, Prague, Czech Republic
| |
Collapse
|
6
|
Bonyadi SZ, Demott CJ, Grunlan MA, Dunn AC. Cartilage-like tribological performance of charged double network hydrogels. J Mech Behav Biomed Mater 2020; 114:104202. [PMID: 33243694 DOI: 10.1016/j.jmbbm.2020.104202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 10/16/2020] [Accepted: 11/06/2020] [Indexed: 10/23/2022]
Abstract
A synthetic hydrogel material may offer utility as a cartilage replacement if it is able to maintain low friction in different sliding environments and achieve bulk mechanical properties to withstand the severe environment of the joint. In this work, we compared the tribological behavior of four double network (DN) hydrogels to that of fresh porcine cartilage in both water and fetal bovine serum (FBS). The DN hydrogels were comprised of a negatively charged 1st network and a 2nd network wherein comonomers of varying charge (i.e. neutral, positive, negative, and zwitterionic) were introduced at 10 wt% to an otherwise neutral network. A steel ball probe was used to perform microindentation tests to determine the surface elastic modulus of the samples and estimate their contact areas during sliding. Friction tests using a stationary probe with a stage that reciprocated at a range of speeds were performed to develop lubrication curves in both water and FBS. We found that the DN hydrogels with a neutral or zwitterionic 2nd network had the lowest friction and shear stresses, notably below that of cartilage. The differences in charge and structure of the samples were more evident in water than in FBS, as the lubrication responses for all the hydrogels spanned a wider range of values. In FBS, the lubrication responses were pushed towards elasto-hydrodynamics with nearly all friction coefficient values falling below 0.3. This indicates that the FBS interacts with the hydrogels and cartilage samples in a similar manner as that of cartilage by maintaining a robust layer of solution at the interface during sliding. These DN hydrogels prove to fulfill, and in some cases surpass, the lubrication demands for cartilage replacement in load bearing joints.
Collapse
Affiliation(s)
- Shabnam Z Bonyadi
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Connor J Demott
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA
| | - Melissa A Grunlan
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA; Department of Materials Science & Engineering, Texas A&M University, College Station, TX, USA; Department of Chemistry, Texas A&M University, College Station, TX, USA
| | - Alison C Dunn
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
| |
Collapse
|
7
|
|
8
|
Rehor I, Maslen C, Moerman PG, van Ravensteijn BGP, van Alst R, Groenewold J, Eral HB, Kegel WK. Photoresponsive Hydrogel Microcrawlers Exploit Friction Hysteresis to Crawl by Reciprocal Actuation. Soft Robot 2020; 8:10-18. [PMID: 32320334 DOI: 10.1089/soro.2019.0169] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Mimicking the locomotive abilities of living organisms on the microscale, where the downsizing of rigid parts and circuitry presents inherent problems, is a complex feat. In nature, many soft-bodied organisms (inchworm, leech) have evolved simple, yet efficient locomotion strategies in which reciprocal actuation cycles synchronize with spatiotemporal modulation of friction between their bodies and environment. We developed microscopic (∼100 μm) hydrogel crawlers that move in aqueous environment through spatiotemporal modulation of the friction between their bodies and the substrate. Thermo-responsive poly-n-isopropyl acrylamide hydrogels loaded with gold nanoparticles shrink locally and reversibly when heated photothermally with laser light. The out-of-equilibrium collapse and reswelling of the hydrogel is responsible for asymmetric changes in the friction between the actuating section of the crawler and the substrate. This friction hysteresis, together with off-centered irradiation, results in directional motion of the crawler. We developed a model that predicts the order of magnitude of the crawler motion (within 50%) and agrees with the observed experimental trends. Crawler trajectories can be controlled enabling applications of the crawler as micromanipulator that can push small cargo along a surface.
Collapse
Affiliation(s)
- Ivan Rehor
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands.,Faculty of Chemical Engineering, UCT Prague, Prague, Czech Republic.,Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Charlie Maslen
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands.,Faculty of Chemical Engineering, UCT Prague, Prague, Czech Republic
| | - Pepijn G Moerman
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands
| | - Bas G P van Ravensteijn
- Netherlands Organization for Applied Scientific Research (TNO), Materials Solutions, Eindhoven, The Netherlands
| | - Renee van Alst
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands
| | - Jan Groenewold
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands.,Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou, China
| | - Huseyin Burak Eral
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands.,Process and Energy Laboratory, 3ME Faculty, TU Delft, Delft, The Netherlands
| | - Willem K Kegel
- Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands
| |
Collapse
|
9
|
Pradal C, Yakubov GE, Williams MAK, McGuckin MA, Stokes JR. Lubrication by biomacromolecules: mechanisms and biomimetic strategies. BIOINSPIRATION & BIOMIMETICS 2019; 14:051001. [PMID: 31212257 DOI: 10.1088/1748-3190/ab2ac6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Biomacromolecules play a key role in protecting human biointerfaces from friction and wear, and thus enable painless motion. Biomacromolecules give rise to remarkable tribological properties that researchers have been eager to emulate. In this review, we examine how molecules such as mucins, lubricin, hyaluronic acid and other components of biotribological interfaces provide a unique set of rheological and surface properties that leads to low friction and wear. We then highlight how researchers have used some of the features of biotribological contacts to create biomimetic systems. While the brush architecture of the glycosylated molecules present at biotribological interfaces has inspired some promising polymer brush systems, it is the recent advance in the understanding of synergistic interaction between biomacromolecules that is showing the most potential in producing surfaces with a high lubricating ability. Research currently suggests that no single biomacromolecule or artificial polymer successfully reproduces the tribological properties of biological contacts. However, by combining molecules, one can enhance their anchoring and lubricating capacity, thus enabling the design of surfaces for use in biomedical applications requiring low friction and wear.
Collapse
Affiliation(s)
- Clementine Pradal
- School of Chemical Engineering, The University of Queensland, St Lucia, Queensland, Australia
| | | | | | | | | |
Collapse
|
10
|
Mathis CH, Simič R, Kang C, Ramakrishna SN, Isa L, Spencer ND. Indenting polymer brushes of varying grafting density in a viscous fluid: A gradient approach to understanding fluid confinement. POLYMER 2019. [DOI: 10.1016/j.polymer.2019.02.040] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
11
|
Nguyen VP, Phi PQ, Choi ST. Tribological Behavior of Grafted Nanoparticle on Polymer-Brushed Walls: A Dissipative Particle Dynamics Study. ACS APPLIED MATERIALS & INTERFACES 2019; 11:11988-11998. [PMID: 30821436 DOI: 10.1021/acsami.8b19001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two contacting surfaces grafted with polymer brushes have potential applications due to their extraordinary lubricating behavior. However, the polymer brushes may have poor mechanical stability under high normal and shear stresses, which is a challenge for practical usage of polymer brush systems. In this study, we propose the use of grafted nanoparticles as nanobearings on polymer-brush-coated surfaces to alleviate the harsh working conditions of polymer brushes and to improve their mechanical stability. We have performed dissipative particle dynamics (DPD) simulations to investigate the tribological interaction between grafted nanoparticle and parallel walls with noncharged polymer brushes in the presence of explicit solvent. The influences of several parameters (solvent quality, brush miscibility, etc.) on the tribological behavior of the system are investigated. The grafted nanoparticle obviously acts as a nanobearing that partially replaces the sliding contact between two brushed walls with rolling contact between the grafted nanoparticle and two brushed walls and reduces the number of DPD particles withstanding high force. Although the introduction of the grafted nanoparticle into polymer-brushed walls increases the friction coefficient by 20-30%, it does not greatly decrease lubrication of the brushed walls, while still helping in stabilizing the system of polymer brushes to be used with liquids with low viscosity, such as water. The DPD simulation results and analysis performed in this study would be beneficial in designing systems with polymer-brushed surfaces and grafted nanoparticles.
Collapse
Affiliation(s)
- Vinh Phu Nguyen
- School of Mechanical Engineering , Chung-Ang University , 84 Heukseok-Ro , Dongjak-Gu, Seoul 06974 , Republic of Korea
| | - Phuoc Quang Phi
- School of Mechanical Engineering , Chung-Ang University , 84 Heukseok-Ro , Dongjak-Gu, Seoul 06974 , Republic of Korea
| | - Seung Tae Choi
- School of Mechanical Engineering , Chung-Ang University , 84 Heukseok-Ro , Dongjak-Gu, Seoul 06974 , Republic of Korea
| |
Collapse
|
12
|
Pidhatika B, Nalam PC. Investigation of design parameters in generating antifouling and lubricating surfaces using hydrophilic polymer brushes. J Appl Polym Sci 2019. [DOI: 10.1002/app.47659] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Bidhari Pidhatika
- Laboratory for Surface Science and Technology, Department of MaterialsETH Zürich Vladimir‐Prelog‐Weg 1‐5/10, 8093, Zurich Switzerland
| | - Prathima C. Nalam
- Laboratory for Surface Science and Technology, Department of MaterialsETH Zürich Vladimir‐Prelog‐Weg 1‐5/10, 8093, Zurich Switzerland
| |
Collapse
|
13
|
Singh M, Kang C, Ilg P, Crockett R, Kröger M, Spencer ND. Combined Experimental and Simulation Studies of Cross-Linked Polymer Brushes under Shear. Macromolecules 2018; 51:10174-10183. [PMID: 32063653 PMCID: PMC7018396 DOI: 10.1021/acs.macromol.8b01363] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 10/24/2018] [Indexed: 12/11/2022]
Abstract
We have studied the effect of cross-linking on the tribological behavior of polymer brushes using a combined experimental and theoretical approach. Tribological and indentation measurements on poly(glycidyl methacrylate) brushes and gels in the presence of dimethylformamide solvent were obtained by means of atomic force microscopy. To complement experiments, we have performed corresponding molecular dynamics (MD) simulations of a generic bead-spring model in the presence of explicit solvent and cross-linkers. Our study shows that cross-linking leads to an increase in friction between polymer brushes and a counter-surface. The coefficient of friction increases with increasing degree of cross-linking and decreases with increasing length of the cross-linker chains. We find that the brush-forming polymer chains in the outer layer play a significant role in reducing friction at the interface.
Collapse
Affiliation(s)
- Manjesh
K. Singh
- Laboratory
for Surface Science and Technology, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Chengjun Kang
- Laboratory
for Surface Science and Technology, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Patrick Ilg
- School
of Mathematical, Physical and Computational Sciences, University of Reading, Reading RG6 6AX, United Kingdom
| | - Rowena Crockett
- Swiss
Federal Laboratories for Materials Science and Technology (EMPA), CH-8600 Dübendorf, Switzerland
| | - Martin Kröger
- Polymer
Physics, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Nicholas D. Spencer
- Laboratory
for Surface Science and Technology, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
| |
Collapse
|
14
|
Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow. LUBRICANTS 2018. [DOI: 10.3390/lubricants6030064] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The present study provides molecular insight into the mechanisms underlying energy dissipation and lubrication of a smooth contact lubricated by an ionic liquid. We have performed normal and lateral force measurements with a surface forces apparatus and by colloidal probe atomic force microscopy on the following model systems: 1-ethyl-3-methyl imidazolium bis-(trifluoro-methylsulfonyl) imide, in dry state and in equilibrium with ambient (humid) air; the surface was either bare mica or functionalized with a polymer brush. The velocity-dependence of the friction force reveals two different regimes of lubrication, boundary-film lubrication, with distinct characteristics for each model system, and fluid-film lubrication above a transition velocity V∗. The underlying mechanisms of energy dissipation are evaluated with molecular models for stress-activated slip and flow, respectively. The stress-activated slip assumes that two boundary layers (composed of ions/water strongly adsorbed to the surface) slide past each other; the dynamics of interionic interactions at the slip plane and the strength of the interaction dictate the change in friction -decreasing, increasing or remaining constant- with velocity in the boundary-film lubrication regime. Above a transition velocity V∗, friction monotonically increases with velocity in the three model systems. Here, multiple layers of ions slide past each other (“flow”) under a shear stress and friction depends on a shear-activation volume that is significantly affected by confinement. The proposed friction model provides a molecular perspective of the lubrication of smooth contacts by ionic liquids and allows identifying the physical parameters that control friction.
Collapse
|
15
|
Yu K, Hodges C, Biggs S, Cayre OJ, Harbottle D. Polymer Molecular Weight Dependence on Lubricating Particle–Particle Interactions. Ind Eng Chem Res 2018. [DOI: 10.1021/acs.iecr.7b04609] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Kai Yu
- School
of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Chris Hodges
- School
of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Simon Biggs
- Faculty
of Engineering, Architecture and Information Technology, The University of Queensland, St Lucia, Queensland 4072, Australia
| | - Olivier J. Cayre
- School
of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - David Harbottle
- School
of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| |
Collapse
|
16
|
Shoaib T, Heintz J, Lopez-Berganza JA, Muro-Barrios R, Egner SA, Espinosa-Marzal RM. Stick-Slip Friction Reveals Hydrogel Lubrication Mechanisms. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:756-765. [PMID: 28961012 DOI: 10.1021/acs.langmuir.7b02834] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The lubrication behavior of the hydrated biopolymers that constitute tissues in organisms differs from that outlined by the classical Stribeck curve, and studying hydrogel lubrication is a key pathway to understand the complexity of biolubrication. Here, we have investigated the frictional characteristics of polyacrylamide (PAAm) hydrogels with various acrylamide concentrations, exhibiting Young's moduli (E) that range from 1 to 40 kPa, as a function of applied normal load and sliding velocities by colloid probe lateral force microscopy. The speed-dependence of the friction force shows an initial decrease in friction with increasing velocity, while, above a transition velocity V*, friction increases with speed. This study reveals two different boundary lubrication mechanisms characterized by distinct scaling laws. An unprecedented and comprehensive study of the lateral force loops reveals intermittent friction or stick-slip above and below V*, with characteristics that depend on the hydrogel network, applied load, and sliding velocity. Our work thus provides insight into the closely tied parameters governing hydrogel lubrication mechanisms, and stick-slip friction.
Collapse
Affiliation(s)
- Tooba Shoaib
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States
| | - Joerg Heintz
- Health Care Engineering Systems Center, University of Illinois at Urbana-Champaign , 1206 West Clark Street, Urbana, Illinois 61801, United States
| | - Josue A Lopez-Berganza
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States
| | - Raymundo Muro-Barrios
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States
| | - Simon A Egner
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States
| | - Rosa M Espinosa-Marzal
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States
| |
Collapse
|
17
|
Ramakrishna SN, Cirelli M, Divandari M, Benetti EM. Effects of Lateral Deformation by Thermoresponsive Polymer Brushes on the Measured Friction Forces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:4164-4171. [PMID: 28394137 DOI: 10.1021/acs.langmuir.7b00217] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The nanotribological properties of hydrophilic polymer brushes are conveniently analyzed by lateral force microscopy (LFM). However, the measurement of friction for highly swollen and relatively thick polymer brushes can be strongly affected by the tendency of the compliant brush to be laterally deformed by the shearing probe. This phenomenon induces a "tilting" in the recorded friction loops, which is generated by the lateral bending and stretching of the grafts. In this study we highlight how the brush lateral deformation mainly affects the friction measurements of swollen PNIPAM brushes (below LCST) when relatively short scanning distances are applied. Under these conditions, the energy dissipation recorded by LFM is almost uniquely determined by stretching and bending of the compliant brush back and forth along the scanning direction, and it is not correlated to dynamic friction between two sliding surfaces. In contrast, when the scanning distance applied during LFM is relevantly longer than the brush lateral deformation, sliding of the probe on the brush interface becomes dominant, and a correct measurement of dynamic friction can be accomplished. By increasing the temperature above the LCST, the PNIPAM brushes undergo dehydration and assume a collapsed morphology, thereby hindering their lateral deformation by scanning probe. Hence, at 40 °C in water the recorded friction loops do not show any tilting and LFM accurately describes the dynamic friction between the probe and the polymer surface.
Collapse
Affiliation(s)
- Shivaprakash N Ramakrishna
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich , Vladimir-Prelog-Weg 5/10, 8093 Zurich, Switzerland
| | - Marco Cirelli
- Department of Materials Science and Technology of Polymers, MESA + Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Mohammad Divandari
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich , Vladimir-Prelog-Weg 5/10, 8093 Zurich, Switzerland
| | - Edmondo M Benetti
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich , Vladimir-Prelog-Weg 5/10, 8093 Zurich, Switzerland
| |
Collapse
|
18
|
Nalam PC, Lee HS, Bhatt N, Carpick RW, Eckmann DM, Composto RJ. Nanomechanics of pH-Responsive, Drug-Loaded, Bilayered Polymer Grafts. ACS APPLIED MATERIALS & INTERFACES 2017; 9:12936-12948. [PMID: 28221026 DOI: 10.1021/acsami.6b14116] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Stimuli-responsive polymer films play an important role in the development of smart antibacterial coatings. In this study, we consider complementary architectures of polyelectrolyte films, including a thin chitosan layer (CH), poly(acrylic acid) (PAA) brushes, and a bilayer structure of CH grafted to PAA brushes (CH/PAA) as possible candidates for targeted drug delivery platforms. Atomic force microscopy (AFM) was employed to study the structure-mechanical property relationship for these mono- and bi-layered polymer grafts at pH 7.4 and 4.0, corresponding to physiological and biofilm formation conditions, respectively. Herein, the surface interactions between polymer grafts and the negatively charged silica colloid attached to an AFM lever are considered as representative interactions between the antibacterial coating and a bacteria/biofilm. The bilayered structure of CH/PAA showed significantly reduced adhesive interactions in comparison to pure CH but slightly higher interactions in comparison to PAA films. Among PAA and CH/PAA films, upon grafting CH over the PAA brushes, the normal stiffness increased by 10-fold at pH 7.4 and 20-fold at pH 4.0. Notably, the study also showed that the addition of an antibiotic drug such as multicationic Tobramycin (TOB) impacts the mechanical properties of the antibacterial coatings. Competition between TOB and water molecules for the PAA chains is shown to determine the structural properties of PAA and CH/PAA films loaded with TOB. At high pH (7.4), the TOB molecules, which remain multicationic, strongly interact with polyanionic PAA, thereby reducing the film's compressibility. On the contrary, at low pH (4.0), the water molecules preferentially interact with TOB in comparison to uncharged PAA chains and, upon TOB release, results in a stronger film collapse together with an increase in adhesive interactions between the probe, the surface, and the elastic modulus of the film. The bacterial proliferation on these platforms when compared to the measured mechanical properties shows a direct correlation; hence, understanding nanomechanical properties can provide insights into designing new antibacterial polymer coatings.
Collapse
Affiliation(s)
| | | | - Nupur Bhatt
- Department of Molecular Biology and Genetics, Cornell University , Ithaca, New York 14853-2703, United States
| | | | | | | |
Collapse
|
19
|
Riley JK, Tilton RD. Sequential Adsorption of Nanoparticulate Polymer Brushes as a Strategy To Control Adhesion and Friction. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:11440-11447. [PMID: 27734683 DOI: 10.1021/acs.langmuir.6b02963] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
This work investigates surface forces that result from adsorbed layers of silica nanoparticles with grafted pH-responsive, cationic poly(2-(dimethylamino)ethyl methacrylate) brushes (SiO2-g-PDMAEMA) and how adhesive bridging forces can be suppressed and friction forces reduced by "backfilling" these heterogeneous adsorbed layers with nonionic poly(ethylene oxide) star copolymers (Star PEO45MA). Adsorption of SiO2-g-PDMAEMA and Star PEO45MA to silica is measured as a function of pH by quartz crystal microbalance with dissipation (QCM-D) in order to evaluate the electrostatically driven adsorption of SiO2-g-PDMAEMA and hydrogen-bonding-driven adsorption of Star PEO45MA. Force measurements performed using colloidal probe force microscopy show the strong role that limited surface coverage plays in adhesive bridging forces between silica with adsorbed SiO2-g-PDMAEMA, while Star PEO45MA adsorption produces purely repulsive steric interactions. Bridging between SiO2-g-PDMAEMA-coated surfaces produces frictional forces that tend to be larger than those acting between bare surfaces at similar normal loads, while friction is consistently decreased by Star PEO45MA adsorption. Sequential adsorption of SiO2-g-PDMAEMA and Star PEO45MA generates high-coverage mixed nanoparticulate brush layers with uniformly repulsive normal forces and reduced friction forces. Adsorption and force measurements reveal that Star PEO45MA not only adsorbs to silica but also binds to SiO2-g-PDMAEMA. The latter allows sequential adsorption of the two components to produce mixed multilayers. The mixed SiO2-g-PDMAEMA/Star PEO45MA multilayers exhibit larger layer thicknesses, no bridging, and sustained smooth friction, highlighting their potential usefulness as aqueous boundary lubricant layers.
Collapse
Affiliation(s)
- John K Riley
- Center for Complex Fluids Engineering, ‡Department of Chemical Engineering, and §Department of Biomedical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Robert D Tilton
- Center for Complex Fluids Engineering, ‡Department of Chemical Engineering, and §Department of Biomedical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| |
Collapse
|
20
|
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.
Collapse
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.
| |
Collapse
|
21
|
Kalasin S, Santore MM. Near-Surface Motion and Dynamic Adhesion during Silica Microparticle Capture on a Polymer (Solvated PEG) Brush via Hydrogen Bonding. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b01977] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Surachate Kalasin
- Department of Polymer Science
and Engineering, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| | - Maria M. Santore
- Department of Polymer Science
and Engineering, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States
| |
Collapse
|
22
|
Singh MK, Ilg P, Espinosa-Marzal RM, Kröger M, Spencer ND. Polymer Brushes under Shear: Molecular Dynamics Simulations Compared to Experiments. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:4798-4805. [PMID: 25830715 DOI: 10.1021/acs.langmuir.5b00641] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Surfaces coated with polymer brushes in a good solvent are known to exhibit excellent tribological properties. We have performed coarse-grained equilibrium and nonequilibrium molecular dynamics (MD) simulations to investigate dextran polymer brushes in an aqueous environment in molecular detail. In a first step, we determined simulation parameters and units by matching experimental results for a single dextran chain. Analyzing this model when applied to a multichain system, density profiles of end-tethered polymer brushes obtained from equilibrium MD simulations compare very well with expectations based on self-consistent field theory. Simulation results were further validated against and correlated with available experimental results. The simulated compression curves (normal force as a function of surface separation) compare successfully with results obtained with a surface forces apparatus. Shear stress (friction) obtained via nonequilibrium MD is contrasted with nanoscale friction studies employing colloidal-probe lateral force microscopy. We find good agreement in the hydrodynamic regime and explain the observed leveling-off of the friction forces in the boundary regime by means of an effective polymer-wall attraction.
Collapse
Affiliation(s)
| | - Patrick Ilg
- §School of Mathematical and Physical Sciences, University of Reading, Reading RG6 6AX, United Kingdom
| | - Rosa M Espinosa-Marzal
- ∥Laboratory for Smart Interfaces in Environmental Nanotechnology, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, Illinois 61801, United States
| | | | | |
Collapse
|
23
|
Li B, Yu B, Wang XL, Guo F, Zhou F. Correlation between conformation change of polyelectrolyte brushes and lubrication. CHINESE JOURNAL OF POLYMER SCIENCE 2014. [DOI: 10.1007/s10118-015-1564-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|