Relaxation time of confined liquids under shear

Abstract

Ultrathin films of simple nonpolar molecular fluids (3-8 segmental dimensions thick) show a strikingly long relaxation time in response to oscillatory shear when confined between mica plates at 27 °C. When the shear rate exceeds this inverse time, the effective viscosity decays as an apparent power law in the shear rate, implying considerable distortion of the dynamic structure. The relaxation time is orders of magnitude longer than the Brownian relaxation time in the bulk state and may reflect collective motions induced by confinement.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Experiments [1035][1036][1037][1038][1039], simulations [999,1017,1040,1041] and theory [1042,1043] indicate that the degree of slip depends on the shear rate. Slip seems to occur only from a certain critical shear rate on and it increases with the shear rate.…”

Density and Phase State of a Confined Nonpolar Fluid

“…The experimental observation of first-order confinement-induced freezing is based on the onset of a static friction and a sudden, manyorder-of-magnitude increase in viscosity when the fluid is confined to a particular separation distance [3][4][5]7,9,10]. Other experiments observed viscoelasticity in the fluid prior to the onset of a critical shear stress [1,11,12] and a continuous transition in the viscosity [2,[13][14][15][16][17][18], leading to the conclusion that the fluid was approaching a glass transition. It has been suggested that the experimental results supporting either of these theories are fundamentally in agreement and that the conflicting models arise from differences in resolution and interpretation of the results [19].…”

Nanorheology of liquid alkanes

“…Differences in the dynamic response from the bulk behavior are quite dramatic [l]. The effective viscosities of thin films rise orders of magnitude above the bulk values with a corresponding increase in the molecular relaxation times [3]. However, it should be recognized that dynamical experiments with extensions of the surface force apparatus are conducted a t strain rates (10 -10' s-'): orders of magnitude below the strain rates which are found in the lubrication of disk drives, of micromachines, and of camshaft lifters in automobile engines (ca.…”