Frictional Dissipation in a Polymer Bilayer System

Abstract

Sliding friction between a silicon tip and a polymer bilayer system consisting of a polystyrene (PS) film covered with a few-nanometers-thick capping layer of hard plasma polymer is studied using friction force microscopy. The system was chosen to enable subsurface dissipation channels to be distinguished from surface friction. Frictional energy dissipation in the underlayer can be identified through the kinetics of the polymer relaxation modes that we measured using nanoscale friction experiments as a function of sample temperature, scanning velocity, and applied load. We found a strong nonlinear increase in friction as a function of applied load around the glass-transition temperature of the PS underlayer. This behavior is a clear signature of frictional dissipation occurring in the volume of the polystyrene layer, well below the surface of the sample. The time-temperature kinetics associated with frictional energy dissipation into the PS was found to be in agreement with the known material properties of PS. Moreover, the data was found to support the hypothesis that the observed friction can be understood as the sum of friction resulting from the relaxation process in the polymer underlayer induced by stress due to the sliding of the tip and a second term associated with dissipation due to sliding friction on the capping layer.

Friction anomalies at first-order transition spinodals: 1T-TaS2

“…The peak height is approximately 1.5-2 times higher than the average friction signal away from the transition point, while the peak width is about 2-5 K. Results from further experiments reproduce these values. In contrast to published contact friction versus temperature results [25,26], our result shows a very sharp and distinct transformation behavior, as qualitatively expected from the spinodal theory. It should be noted that in our experiments inducing the phase transition always required multiple scanning of the sample surface.…”

“…Results from further experiments reproduce these values. In contrast to published contact friction versus temperature results [22,23], our result shows a very sharp and distinct transformation behavior, as is indeed expected from the spinodal theory.…”

Nanoscale friction and wear of a polymer coated with graphene

“…The temperature dependence of friction can potentially allow one to probe different relaxation mechanisms in the polymer [ 33 – 34 ]. In our previous work [ 23 ], we extensively investigated the temperature dependence of friction of bare PVA.…”

Tribological Analysis of Contacts Between Glass and Tungsten Carbide Near the Glass Transition Temperature

“…In this context, measurements with varying maximum temperature might determine threshold temperatures for the hysteretic behavior. In addition, measuring the velocity dependence should be instructive, since both mechanical analysis and nanotribological AFM studies have highlighted the effects of strain rates on the internal dissipation [17,18,45]. Concerning PGM, such experiments are relevant, since they help to develop a basic understanding of tribological processes between molds and glass.…”

“…These materials have been extensively studied by techniques like e.g., dynamical mechanical analysis (DMA) [9][10][11][12] and the resulting temperature dependence of the elastic and viscoelastic behavior can be explained by internal relaxations of the polymers. The link between tribology and these internal relaxations becomes particularly clear in recent analysis by friction force microscopy which directly correlates the different temperature-dependent transitions within the polymers to characteristic energy barriers derived from nanoscale friction [13][14][15][16][17][18]. But already for macroscopic systems these mechanisms were anticipated based on experiments, which explored the influence of velocity and temperature on polymer friction [19].…”