Supersoft Elastic Bottlebrush Microspheres with Stimuli-Responsive\nColor-Changing Properties in Brine

Abstract

Solvent-free\nsupersoft elastomer is highly desirable for building\nphotonic structures with significant stimuli-responsive color changes.\nWe report supersoft elastic porous microspheres with vivid structural\ncolors obtained via self-assembly of amphiphilic bottlebrush block\ncopolymers at the water/oil interface templated by ordered water-in-oil-in-water\ndouble emulsions. The porous structure is composed of cross-linked\nbottlebrush polydimethylsiloxane (PDMS) as the supersoft elastic skeleton\nand bottlebrush poly­(ethylene oxide) (PEO) as the internal responsive\nlayer. The obtained microspheres show large reversible volume changes\nthrough well-controlled dehydration or hydration of PEO in response\nto salt ions in an aqueous environment. As a result, full-spectrum\ncolors are obtained dependent on different salt concentrations. In-situ\nobservation of color reflection of a microsphere indicates a gradual\nstructural transition from the outside to the inside corresponding\nto migration of water molecules and salt ions. Moreover, rod-like\nbottlebrush PEO exhibits an anion-induced salting-out behavior different\nfrom that of random coil polymers. The significantly responsive behaviors\nof bottlebrush block copolymer (BBCP) assemblies in the presence of\nsalt ions primarily rely on the supersoft elastic skeleton of the\nporous structure, providing a facile route to the creation of stimuli-responsive\nphotonic materials by low-cost self-assembly methods.