Computer simulation of molecular shape transitions in adsorbed polymers under confinement conditions

Abstract

The structural and dynamical properties of polymer-covered surfaces under confinement and crowding effects are key to many applications. Earlier work showed the occurrence of “escape transitions” in small uncompressed clusters (or “islands”) even for repulsive polymers. These transitions involve a switch from evenly-compact configurations (“trapped chains”), to uneven compactness (“escaped chains”). Here, we address a complementary question: if the crowding is reduced by having fewer neighbours, can an external compression produce “escaped configurations”? To this end, we focused on the confinement of grafted polymers. At low compression, the inter-chain entanglement increases with excluded volume as chains swell and interpenetrate, up to a critical chain length where the behaviour is reversed. We conclude that, when few chains are present or if a larger ensemble of them is arranged symmetrically, compression induces chain avoidance without inducing escape transitions. The switch in mechanism depends mostly on crowding, and not on the applied pressure.