Macromodel approach to experimental study of polymer brushes rubbing

For experimental studies of polymer brushes friction a simple macromodel ap proach using ordinary tooth brushes with different stiffness was proposed. Experiments were performed on pairs of brushes with various mutual penetrat ions and speed of displacement, and a force-displacement response during cy clic shift in two directions was studied. Experimental results reveal two m echanisms of friction, so-called 'slipping-pulling' and 'rake-on-rake'. The 'attraction' effect was observed at the beginning of the brushes moving cy cle, connected with the friction of filament ends along axis. Controversial influence of friction between constituent elementary filaments of opposite brushes and their bend deformations during mutual displacement on normal r eaction was shown. Contrasting with the shear force, the normal repulsive r eaction for mild brushes is stronger than that for rigid brushes due to pre sence of different rubbing mechanism. (C) 1998 Published by Elsevier Scienc e S.A. All rights reserved.