Flexible Honeycomb Films

Abstract

Micro-porous polymer films with self-assembled honeycomb morphology produced by the 'breath figure' (BF) [1] technique have distinct advantages over other lithographic techniques: there is no need for expensive equipment, and it is a simple and cheap process that can control pore sizes through varying casting conditions. [2] These ordered porous films have potential applications particularly in biotechnology industries.131 Similar films have been made from a variety of polymers, for example, star polymers, [4] and core cross-linked star (CCS) polymers.151 The BF process involves the evaporation of a volatile solvent from a polymer solution in the presence of atmospheric humidity. [1] The cooled solution surface (evaporative cooling) induces condensation of water droplets. These droplets self-assemble into an ordered array, and are stabilized by a precipitating polymer layer. After complete evaporation, a honeycomb-like scaffold remains. The porous films prepared by the BF technique are often prepared from polymers with a high glass transition temperature Tg, and hence brittle films are prepared, leading to high degree of cracking. If this process is to lead to commercial products, a new strategy is needed - the utilization of soft, visco-elastic polymer precursors.