Light-Controlled Interfacial Self-Assembly of Bottlebrush Amphiphiles toward Highly Tunable Photonic Materials

We present a "light-controlled self-assembly" strategy to enhance the interfacial binding strength of amphiphilic bottlebrush block copolymers (BBCPs) at the water/oil (w/o) interface. A minor quantity (0.5–4 wt %) of o-nitrobenzyl ester units is introduced into the hydrophilic block of the BBCPs, leading to the formation of a semiflexible chain conformation. Under UV radiation, carboxylic acid groups are generated in a quantitative manner by changing the exposure time. This results in the strengthened anchoring effect, as made evident by the increase in the elastic modulus of the monolayer BBCP film. Furthermore, the presence of acid groups induces a significant expansion in the hydrophilic block chain when the BBCPs are adsorbed at the w/o interface of an ordered w/o/w complex emulsion system. This expansion results in a decrease in the spherical curvature of the internal droplets, leading to larger pore diameters in the resulting photonic supraballs. By leveraging this approach, we can easily achieve complex self-assembled structures with unprecedented periodicities (142–556 nm) and photonic band gaps (374–1167 nm) using a minimal number of BBCPs as the fundamental building blocks. The resulting photonic pigments hold significant potential for applications as safe colorants in cosmetics, coatings, inks, and more, as well as IR-reflective materials for biomimetic thermoregulation.