Stick slip behavior

Foam rheology has been a challenging area of research of interest for the yield behavior and stick-slip flow behavior (see the review by Kraynik [229]). Recent studies by Durian and co-workers combine simulations [230] and a dynamic light scattering technique suited to turbid systems [231], diffusing wave spectroscopy (DWS), to characterize coarsening and shear-induced rearrangements in foams. The dynamics follow stick-slip behavior similar to that found in earthquake faults and friction (see Section XU-2D). 

Mishin, Y., Suzuki, A., Uberuaga, B.P., Voter, A.F. Stick-slip behavior of grain boundaries studied by accelerated molecular dynamics. Phys. Rev. B 2007, 75, 224101-1-7. 

The frictional properties of PTFE arc unique Its unusually low static coefficient of friction decreases with increasing load and is lower than the dynamic coefficient of friction. This precludes stick-slip behavior. The low surface energy also prevents wetting by liquids other than low-surface-tension fluids like fluorocarbons. 

Yoshizawa and Israelachvili interpreted the stick-slip behavior at lower... 

The stick-slip behavior discussed above, originates from dynamic order transitions of mechanically confined fluids. It should not be confused with the true... 

Figure 9. Molecular stick-slip behavior measured on anisotropic, rowlike, surface lattice of a lipid film at a drag velocity of 1 nm/s. (a) Sliding direction perpendicular to the row-like structure, (b) sliding direction 6(f to the row-like structure. Reprinted with permission from reference 62. The American Physical Society, 1994.

In the chain-parallel direction, only the HOPE showed a periodic stick slip behavior with a repeat distance of ca. 2.5 A. This distance is equal to the repeat unit of polyethylene (16, 20). For PTFE the LFM friction loops in our experiments did not reveal any stick slip behavior. Thus, in this case, we cannot determine the value of do in the chain-parallel direction. In this case we can, however, assume that the value of d is close to 0. Based on equation 1, the friction anisotropy is therefore expected to be larger for PTFE, than that for HDPE. For a semi-quantitative comparison of friction forces predicted by equation (1) on one hand and experimental results obtained on highly oriented polymer surfaces on the other hand, one should be... 

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