Effect of compression on the molecular shape of polymer mushrooms with variable stiffness

Abstract

Under confinement, the average shape of a polymer chain is modified in interesting ways. In this work, we discuss how confinement affects the mean geometrical properties of wormlike polymers with variable flexibility and monomer–monomer interaction. Here, we consider a polymer mushroom, i.e., a single chain that is permanently anchored to a flat surface by an end point. Compression is introduced by confining the chains inside an infinite slab with parallel hard walls. Regarding polymer shape, we focus on two large-scale geometrical properties that are not correlated a priori: the chain’s size and its entanglement complexity. Using Monte Carlo simulations, we have analyzed the behavior of these two properties under confinement for a range of potential energy functions. A recurrent pattern of shape transitions emerges, as indicated by changes in the correlation between mean size and entanglements. Our results show that, whereas a flexible polymer with strong self-attraction sustains high compression without deforming, polymers that are either too rigid or too weakly self-attracting are “flattened” by slight compression. Furthermore, we find a general relation between molecular size and entanglements that is valid over a range of polymer models and levels of confinement. We conclude that chain stiffness influences less the compressive behavior of a polymer than chain self-interactions.