Structure and Shear Response in Nanometer-Thick Films
TLDR
In this article, the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described, and a power law is found for a wide range of parameters, and extends to lower and lower velocities as a glass transition is approached.Abstract:
Simulations of the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described. Confining walls introduce layering and in-plane order in the adjacent fluid. The latter is essential to transfer of shear stress. As the film thickness is decreased, by increasing pressure or decreasing the number of molecular layers, the entire film may undergo a phase transition. Spherical molecules tend to crystallize, while short-chain molecules enter a glassy state with strong local orientational and translational order. These phase transitions lead to dramatic changes in the response of the film to imposed shear velocities v. Spherical molecules show an abrupt transition from Newtonian response to a yield stress as they crystallize. Chain molecules exhibit a continuously growing regime of non-Newtonian behavior where the shear viscosity drops as v−2/3 at constant normal load. The same power law is found for a wide range of parameters, and extends to lower and lower velocities as a glass transition is approached. Once in the glassy state, chain molecules exhibit a finite yield stress. Shear may occur either within the film or at the film/wall interface. Interfacial shear dominates when films become glassy and when the film viscosity is increased by increasing the chain length.read more
Citations
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Effects of confinement on freezing and melting.
Christiane Alba-Simionesco,Benoit Coasne,Gilberte Dosseh,G. Dudziak,Keith E. Gubbins,Ravi Radhakrishnan,Malgorzata Sliwinska-Bartkowiak +6 more
TL;DR: Both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) are considered and how confinement affects the glass transition is addressed.
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The nonlinear nature of friction
TL;DR: Recent experiments coupled to theoretical modelling have made great advances in unifying apparently diverse phenomena and revealed many subtle and often non-intuitive aspects of matter in motion, which stem from the nonlinear nature of the problem.
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Fluidity of water confined to subnanometre films
TL;DR: It is observed that the effective viscosity of water remains within a factor of three of its bulk value, even when it is confined to films in the thickness range 3.5 ± 1 to 0.0 ± 0.4 nm, which contrasts markedly with the behaviour of organic solvents, whose visCosity diverges when confined to Films thinner than about 5–8 molecular layers.
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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.
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Adsorbed layers and the origin of static friction
TL;DR: A simple and general explanation for the prevalence of static friction is proposed: "Third bodies," such as small hydrocarbon molecules, adsorb on any surface exposed to air and can arrange to lock two contacting surfaces together.
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