Journal ArticleDOI
Shear Forces between Tethered Polymer Chains as a Function of Compression, Sliding Velocity, and Solvent Quality
Phillip A. Schorr,Thomas C. B. Kwan,S. Michael Kilbey,Eric S. G. Shaqfeh, ,‡,‖ and,Matthew Tirrell +4 more
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In this article, the shear forces between polystyrene chains end-tethered to opposing surfaces have been measured with the surface forces apparatus (SFA) in both good and near-ϑ solvents.Abstract:
The shear forces between polystyrene chains end-tethered to opposing surfaces have been measured with the surface forces apparatus (SFA) in both good and near-ϑ solvents. When the shearing velocity was varied, the complex polymer/solvent system responded in a Newtonian-like fashion with the shear force increasing linearly with the shear velocity. The effective viscosity of the end-tethered systems in this Newtonian-like regime was found to be an order of magnitude greater than the viscosity of semidilute solutions of equivalent molecular weight free chains. At larger shear velocities or higher extents of compression, Brownian dynamics simulations suggest the interfacial width will thin, leading to a sublinear increase in the shear force with sliding velocity. Experimental limitations prevented exploration of the higher shear velocities simulated with the Brownian dynamics approach, but increasing confinement eventually did lead to sublinear behavior, in agreement with the simulation prediction.read more
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Lubrication at physiological pressures by polyzwitterionic brushes
Meng Chen,Wuge H. Briscoe,Steven P. Armes,Steven P. Armes,Steven P. Armes,Jacob Klein,Jacob Klein,Jacob Klein +7 more
TL;DR: It is found that surfaces in water bearing polyzwitterionic brushes that were polymerized directly from the surface can have μ values as low as 0.0004, which is attributed primarily to the strong hydration of the phosphorylcholine-like monomers that make up the robustly attached brushes.
Journal ArticleDOI
Molecular mechanisms of synovial joint lubrication
Jacob Klein,Jacob Klein +1 more
TL;DR: In this article, a brush-like phase of charged macromolecules at the surface of the superficial zone of the cartilage was proposed to reduce the friction of synovial joints.
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Polymer brushes on flat and curved surfaces: How computer simulations can help to test theories and to interpret experiments
TL;DR: Theoretical descriptions of static properties of polymer brushes are reviewed, with an emphasis on monodisperse macromolecules grafted to planar, cylindrical, or spherical substrates as mentioned in this paper.
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Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films
TL;DR: In this article, an overview of recent advances that have been achieved in understanding the basic physics of friction and energy dissipation in molecularly thin adsorbed films and the associated impact on friction at microscopic and macroscopic length scales.
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Pairwise frictional profile between particles determines discontinuous shear thickening transition in non-colloidal suspensions.
Jean Comtet,Guillaume Chatté,Antoine Niguès,Lydéric Bocquet,Alessandro Siria,Annie Colin,Annie Colin +6 more
TL;DR: New experimental procedures based on quartz-tuning fork atomic force microscopy measure the pairwise frictional profile between approaching pairs of polyvinyl chloride and cornstarch particles in solvent and show that the normal stress needed to enter the frictional regime at nanoscale matches the critical stress at which shear thickening occurs for macroscopic suspensions.
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Intermolecular and surface forces
TL;DR: The forces between atoms and molecules are discussed in detail in this article, including the van der Waals forces between surfaces, and the forces between particles and surfaces, as well as their interactions with other forces.
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Reduction of frictional forces between solid surfaces bearing polymer brushes
TL;DR: In this paper, the authors measured the lateral forces between sliding brush-bearing surfaces and found a striking reduction in the effective friction coefficients between the surfaces to below their detection limit (μb < 0.001), for contact pressures of around 1 MPa and sliding velocities from zero to 450 nm s−1.
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Simple liquids confined to molecularly thin layers. I. Confinement-induced liquid-to-solid phase transitions
Jacob Klein,Eugenia Kumacheva +1 more
TL;DR: In this paper, a surface force balance with extremely high resolution in measuring shear forces has been used to study the properties of films of the simple organic solvents cyclohexane, octamethylcyclotetrasiloxane, and toluene, confined in a gap between smooth solid surfaces.