Light-Controlled\nInterfacial Self-Assembly of Bottlebrush\nAmphiphiles toward Highly Tunable Photonic Materials

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