The origin of static friction in ultrathin liquid films

Alsten, John Van; Granick, Steve

doi:10.1021/la00094a029

Cited by 61 publications

(22 citation statements)

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“…When a fluid film is confined between two solid surfaces, both types of order may span the entire film. Experimental consequences are oscillations in the normal force with film thickness [15], and phase transitions to solid states that resist shear forces [4,6,7,8].…”

Section: Equilibrium Structurementioning

confidence: 99%

“…Our knowledge of such thin films has increased greatly in recent years due to the development of faster computers and new experimental techniques. Examples of the latter include atomic force microscopy [1,2], the quartz crystal microbalance [3], and the surface forces apparatus (SFA) [4,5,6,7,8,9,10].…”

Section: Introductionmentioning

confidence: 99%

“…In this paper we use molecular dynamics simulations to study the structure and dynamics of fluids in a geometry that models the SFA [4,5,6,7,8,9,10]. In the SFA, fluids are confined between mica plates that are atomically flat over contact diameters of order 100µm.…”

Section: Introductionmentioning

confidence: 99%

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Structure and Shear Response in Nanometer‐Thick Films

Thompson

Robbins

Grest

1995

Israel Journal of Chemistry

169

162

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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, 1 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.

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Section: Equilibrium Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure and Shear Response in Nanometer‐Thick Films

Thompson

Robbins

Grest

1995

Israel Journal of Chemistry

169

162

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“…In the literature, considerable disagreement and conflicting results still exist regarding this subject. Although it is generally agreed upon that a nonpolar fluid becomes more solidlike when confined to a thickness below 4-6 molecular layers [1][2][3][4][5][6][7][8], the molecular interpretation of this phase transition is an area of contention. Two competing theories based on differing experimental results dominate the literature.…”

mentioning

confidence: 99%

Density and Phase State of a Confined Nonpolar Fluid

Kienle

Kuhl

2016

Phys. Rev. Lett.

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Measurements of the mean refractive index of a spherelike nonpolar fluid, octamethytetracylclosiloxane (OMCTS), confined between mica sheets, demonstrate direct and conclusive experimental evidence of the absence of a first-order liquid-to-solid phase transition in the fluid when confined, which has been suggested to occur from previous experimental and simulation results. The results also show that the density remains constant throughout confinement, and that the fluid is incompressible. This, along with the observation of very large increases (many orders of magnitude) in viscosity during confinement from the literature, demonstrate that the molecular motion is limited by the confining wall and not the molecular packing. In addition, the recently developed refractive index profile correction method, which enables the structural perturbation inherent at a solid-liquid interface and that of a liquid in confinement to be determined independently, was used to show that there was no measurable excess or depleted mass of OMCTS near the mica surface in bulk films or confined films of only two molecular layers.

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“…Recently, some progress in understanding several important features of friction was made by investigations of simplified model systems. In particular, atomically smooth mica surfaces in the surface force apparatus [2][3][4][5][6] and computer simulations [7][8][9] have provided new insight. Extended measurements on microscopically rough systems have also helped significantly [10].…”

Section: Introductionmentioning

confidence: 99%

What determines static friction and controls the transition to sliding?

et al. 1995

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We studied the shear response of a confined lubricant layer on approach of the transition to sliding with a surface force apparatus modified for oscillatory shear. In a given experiment, we found that the transition to sliding occurred always around the same deformation amplitude although the shear stress needed to initiate sliding varied up to a factor of two depending on sample history. This suggests the concept of deformation-controlled switching from rest to sliding. The elastic spring-constant, in the stick state, weakened with increasing deformation amplitude. This decrease can be described by a power law when plotted versus the distance to a critical deformation amplitude. The build-up of solid-like behavior after sliding stopped was also gradual and was consistent with a logarithmic time dependence. We suggest a model relating the gradual decrease of stiffness to weakening of the boundary layer, specifically to destruction of some elastic links between molecules or between molecules and the solid surfaces. Static friction (the force that must be overcome at the onset of kinetic motion) is proportional to the number of such links formed during the time of stick.

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The origin of static friction in ultrathin liquid films

Cited by 61 publications

References 0 publications

Structure and Shear Response in Nanometer‐Thick Films

Structure and Shear Response in Nanometer‐Thick Films

Density and Phase State of a Confined Nonpolar Fluid

What determines static friction and controls the transition to sliding?

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