A versatile route to functional biomimetic coatings: ionomers for honeycomb-like structures

Abstract

Highly ordered films were prepared by spreading out carbon disulfide (CS₂) solutions of ionomers over inorganic surfaces and for the first time over an organic surface. These ionomers, i.e. hydrophobic homopolymers or copolymers end-capped by a cationic group, were easily synthesized in a one-step reaction by a control radical process called nitroxide-mediated polymerization. Optical and electronic microscopy observations of the films lead to the definition of new criteria for the formation of such structures. Firstly, the effect of a solid support on the honeycomb structure regularity was studied. By comparing two polar substrates, it was found that a more regular organization is obtained over mica than over glass. This phenomenon may be due to the electrostatic interactions between cationic ionomer ends and oxanions of the mica surface. Moreover, for the first time, highly ordered hexagonal patterns were also created on a flexible and soft polymeric surface, a poly(vinyl chloride) sheet. Secondly, it was found that the characteristics of the polymeric chain of the ionomer and mainly its glass transition temperature play an important role in the process of formation of ordered structures. The iridescent aspect of the films, due to light diffraction and optical interferences, was studied and quantified by spectrogoniometry. Finally, results of measurements of superficial tension are discussed; the presence of a honeycomb film at the surface of a material very significantly enhances its hydrophobicity. All these criteria of highly ordered structures correlated to a water repellency and iridescent behaviours lead to a functional biomimetic material.