Polymer-Brush Lubricated Surfaces with Colloidal Inclusions under Shear Inversion

Abstract

We characterize the response of compressed, sheared polymer-brush bilayers with colloidal inclusions to highly nonstationary inversion processes by means of molecular dynamics simulations and scaling theory. Bilayers with a simple (dimeric) solvent reveal an overshoot for the shear stress, while simulations of dry brushes without explicit solvent molecules fail to display this effect. We demonstrate that mechanical instabilities can be controlled by the inclusion of macromolecular structures, such as colloids of varying softness. Based on a recently developed theory, we suggest a scaling approach to determine a characteristic time for conformational and collective responses.

Water tribology on graphene

“…time, and after some period, t pl , which is usually about 10-20 min (a time which is typical for re-organization of solid surface molecules [18][19][20], it reaches a plateau, denoted by t rest ¼ t pl as demonstrated in Fig. 3a.…”

Polymer brushes on flat and curved surfaces: How computer simulations can help to test theories and to interpret experiments

“…Still another measure of interpenetration is the interpenetration length L , defined by Witten et al139 and used also in the study of sheared brushes 121–124. It is defined as the distance over which in eq 110 the product ϕ 1 ( z )ϕ 2 ( z ) is essentially different from zero.…”

“…The polymer chains in such polymer brushes organize themselves in very soft polymeric layers coating the substrate surface, which are easily perturbed by external stimuli (solvent quality,4, 40–43, 45, 94–97 temperature, applied electrical field and, last but not least, by applied mechanical forces3, 5, 9, 97–124). In this context, also the interaction with nanoparticles,125–130 proteins,131 and free flexible polymers in solutions132–137 are of interest, as well as surfactants or brush–brush interactions or interactions with polymer melts, polymer networks, and so forth138–156 Also the effects of monomer–substrate interactions deserve attention 8…”

Polymer brushes under flow and in other out-of-equilibrium conditions

“…Thus, this review focuses on two aspects only: one aspect is the response of polymer brushes to shear flow 4,6,92,93 and the anomalous reduction of friction when two brushes are sheared against each other. A related problem is the interaction of polymer brushes coating the inner wall of capillaries with fluids flowing into these tubes (''capillary imbibition'' [94][95][96] ).…”