Three-layer structured soft particles to construct photonic paper exhibiting responsive spatio-temporal color patterns

Abstract

Photonic crystals (PCs), which generate vivid colors from periodic physical structures, have attracted considerable attention. However, it is still highly challenging to produce large-scale PC films with high mechanical performance. To address the challenge, a new strategy to fabricate PC films from soft structured latex particles instead of widely used hard particles is reported. The soft latex particles are designed to have a three-layer structure: a responsive poly(acrylic acid) (PAA) corona, hard polystyrene (PSt) shell and soft poly(n-butyl acrylate) (PnBA) core. Such latex particles with easily-tunable and well-defined structures are synthesized from RAFT emulsion polymerization. Thanks to the softness, PCs can be easily achieved by latex casting on various substrates without pre-treatment, leading to a dense, crack-free, and mechanically robust PC film. The as-prepared PC films of the particles with PnBA around 55 wt% can generate vivid colors when the “inks” of water and hydrophilic liquids are applied. The full colors can be achieved by tuning particle size or pH value. Taking advantage of the responsive properties to hydrophilic liquids with different volatilities, both temporary and permanent patterns can be constructed on the PC films, leading to spatio-temporal colorful patterns. The method is simple, scalable-up, and versatile, showing great potentials for practical applications.