Inhomogeneous Structure of Collapsed Polymer Brushes Under Deformation

Abstract

The theory of the equilibrium structure and properties of a planar brush under poor solvent conditions subjected to normal deformations (stretching or compression) is presented. Using a scaling type analysis, we demonstrate that at moderate grafting densities the brush loses its lateral homogeneity and the grafted chains form aggregates (pinned micelles) with globular cores and extended legs connecting the core with the grafting surface. These micelles are stable in a rather wide range of grafting densities provided that the chains are long and the solvent is poor enough so that τ N1/2 >> 1. Scaling relations as well as diagrams of states are obtained. It is shown that the normal deformation of the brush alters boundaries of the micelle stability regime and leads to the rearrangement of the equilibrium micelle structure. Stretching leads to an increase in both the width of the stability region and the number of chains in a micelle whereas compression causes a decrease in these values. Different scenarios of brush deformation are predicted. Hysteresis effects in the processes of interaction between brushes are discussed.