Photocleavage of Covalently Immobilized Amphiphilic Block Copolymer: From Bilayer to Monolayer

Abstract

We developed and verified a method to create a photocleavable smart surface. Using the grafting to approach, we covalently attached an intelligently designed tailor-made diblock copolymer to a silicon wafer. The photocleavable moiety, o-nitrobenzyl (ONB) ester, was integrated into the copolymer at the junction point between the hydrophilic poly(ethylene oxide) (PEO) and the hydrophobic polystyrene (PS) chains. The well-defined azide bearing amphiphilic block copolymer was synthesized via a general stepwise strategy that combines atom transfer radical polymerization (ATRP) and copper(I)-catalyzed azide–alkyne cycloaddition reaction (CuAAC), ending with azidation. The azide end-functionalized copolymer chains were covalently bound to the alkyne-immobilized silicon wafer by CuAAC. The smart surface was exposed to UV irradiation, resulting in photocleavage of the grafted ONB linker. As a result of the photocleavage and subsequent removal of the o-nitrosobenzaldehyde bearing PEO, the PS layer remained on the surface. To confirm the behavior, film thickness and wettability changes were investigated before and after UV irradiation using AFM and contact angle measurements. Integration of photocleavable polymers through covalent grafting to solid surfaces contributes responsiveness to such materials that can find a wide array of applications in advanced devices.