Molecular shape transitions in grafted polymers under geometrical confinement

Abstract

Many applications involve the use of macromolecules at interfaces, including adhesion, lubrication, and the manufacture of surfaces resistant to wear. Modeling these systems requires an understanding of how the dominant conformational features of a macromolecule are modified by the presence of a boundary. In this work, we are interested in monitoring the shape changes that accompany the configurational rearrangements of a single polymer chain near a hard plane. We provide a detailed characterization of essential molecular shape features of compressed grafted chains. These chains are modeled by three-dimensional (off-lattice) walks with excluded-volume interaction, anchored to a flat surface by a terminal point. Compression is induced by confining the chains between two parallel walls. For these systems, we have studied how shape descriptors depend on polymer size and the separation between walls. We show that compression causes a number of nontrivial changes in shape (shape transitions). In particular, we show that the most compact chains found during compression are neither spheroidal nor maximally self-entangled. Maximal entanglements are found in chains that are already mostly “flattened” toward the surface. The present results provide new insights that can be useful in the design of interfaces with targeted properties. © 1996 John Wiley & Sons, Inc.