Layer-by-layer films of stimuli-responsive block copolymer micelles

Abstract

The recently introduced approach of using stimuli-responsive block copolymer micelles (BCMs) as building blocks for layer-by-layer (LbL) assemblies has greatly enhanced the functionality of LbL films. Responsive BCMs supply films with hydrophobic ‘pockets’ that can be ‘opened’ through external triggers. This is enabled by the use of amphiphilic polymers as constituents of micellar cores which undergo dissolution/collapse transitions as a function of environmental stimuli. Whereas the application of these stimuli in solution results in reversible disintegration of stimuli-responsive BCMs to unimers, such disintegration is inhibited within LbL films because of binding of BCM coronal chains with their polymer counterparts. Upon application of environmental stimuli, dissolution/collapse of micellar cores of assembled BCMs results in large-amplitude, reversible swelling/deswelling transitions of the entire film. In addition to the mechanical actuation response, the newly developed BCM-containing films demonstrated efficient control of the uptake and release of small hydrophobic molecules. This approach to constructing responsive assemblies is versatile, can be applied to a wide set of block copolymers with various composition and architecture, and extended to several types of environmental stimuli.