Phase transitions in brushes of homopolymers

Polymer brushes formed by identical macromolecules anchored at the solid-liquid interface may undergo conformational transitions resulting in formation of layered structures with abrupt variation of polymer density ("vertical stratification") or in lateral decomposition that gives rise to nano-patterned interfaces. The intra-brush nanoscale segregation is governed by a balance of intermolecular interactions with conformational entropy of the brush-forming chains and may be triggered by external stimuli that affect the strength of the inter-chain interactions. Both vertical and lateral segregation in the brushes have important implication for applications of brushes for modification of physico-chemical and (bio) interactive properties of interfaces, as well as in biological functions of biopolymer brushes widely found in living nature. While the effects of microphase segregation in polymer brushes are well understood on the basis of existing theories, experimental observation and characterization of such structures using surface-sensitive techniques often remains challenging. Here we present an overview of the state-of-the-art in experimental work on high-resolution structural characterization of polymer brushes in relation to the existing theoretical predictions. The review focusses on planar and spherical brushes. Moreover, consequences for the related case of bottle brush polymers are discussed. (C) 2016 Published by Elsevier Ltd.