Reversible stimuli-responsive nanostructures assembled from amphiphilic block copolymers.

We present a novel route to assemble perpendicular cylinders by converting an asymmetric diblock copolymer from poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA) to poly(styrene-b-acrylic acid) (PS-b-PAA) using an autocatalytic reaction. Upon exposure of the films of PS-b-PAA to water, PAA cylinders constrained by the continuous, glassy PS phase protrude 10 nm above the surface and swell laterally to form mushroom caps, rendering the entire surface hydrophilic. Upon annealing, the original nanostructures re-form demonstrating reversibility of swelling. Because of their stimuli-responsive behavior, these nanoscale materials are excellent candidates for sensors and microfluidic applications.