Friction between ring polymer brushes

Abstract

Friction between ring polymer brush bilayers sliding past each other at melt densities is studied using extensive coarse-grained molecular dynamics simulations and scaling arguments, and the results are compared to the friction between bilayers of linear polymer brushes. We show that for a velocity range spanning over three decades, the frictional forces measured for ring polymer brushes are half of the corresponding friction in the case of linear brushes. In the linear-force regime, the weak inter-digitation between ring brush layers as compared to linear brushes leads also to a lower number of binary collisions between the monomers from opposing brushes. At high velocities, where the thickness of the inter-digitation between bilayers is on the order of monomer size regardless of brush topology, stretched segments of ring polymers adopt the double-stranded conformation. As a result, monomers of the double-stranded segments collide on average less with the monomers of the opposing ring brush even though a similar number of monomers occupies the inter-digitation layer for ring and linear brush bilayers. The numerical data obtained from our simulations are consistent with the proposed scaling analysis. Conformation-dependent friction reduction observed in ring brushes can have important consequences in non-equilibrium bulk systems.

Topological Polymer Chemistry Enters Surface Science: Linear versus Cyclic Polymer Brushes

“…An increase of friction was also recorded at higher applied loads, but this was relevantly decreased compared to the case of two linear brushes sheared against each other. This phenomenon was likely due to the cyclic topology of the grafts on one of the substrates, which suppressed interfacial interdigitation with the linear brush counter‐surface because of the absence of polymer chain ends …”

Topological Polymer Chemistry Enters Surface Science: Linear versus Cyclic Polymer Brushes

“…[45,46] When one surface of the tribo-pair was replaced by C-PEOXA-11 brushes,the corresponding frictional profile overlapped the FL curve obtained for L-PEOXA-11 versus L-PEOXA-11 at relatively low loads.Anincrease of friction was also recorded at higher applied loads,but this was relevantly decreased compared to the case of two linear brushes sheared against each other.T his phenomenon was likely due to the cyclic topology of the grafts on one of the substrates,w hich suppressed interfacial interdigitation with the linear brush counter-surface because of the absence of polymer chain ends. [47,48] This topological characteristic,c oupled with the exceptional conformational barrier generated by C-PEOXA-11 brushes determined the frictional properties of two opposing cyclic brushes shearing against each other (Figure 5a). In this case the recorded friction was extremely low and nearly constant across the whole load range experimented.…”

Loops and Cycles at Surfaces: The Unique Properties of Topological Polymer Brushes

“…The static and dynamic properties of cyclic polymer brushes were also predicted by the theoretical works of Chen‐Xu et al . and Erbaş et al., who employed molecular dynamics simulations to study the structure of cyclic grafts, compared to that of their linear analogues. In particular, for a given grafting density and molar mass, cyclic brushes were envisioned to be more compact and stretched with respect to their linear counterparts, approximating a step‐like segment density profile.…”