Facile Assembly of High-Solid, Responsive Liquid Photonic Crystals via RAFT-Synthesized Colloidal Nanospheres Using Rotary Evaporation

Abstract

Colloidal liquid photonic crystals with high saturation and high solid content are key to achieving their sensitive response, while the preparation of colloidal nanospheres that combine both high stability and monodispersity is still a central technological challenge. Here, we designed and synthesized a series of poly(acrylic acid)n macro chain transfer agents (macro-CTAs), PAAn-CDPA, n = 10, 20, 40, via reversible addition-fragmentation chain transfer (RAFT) polymerization. These macro-CTAs were then utilized in RAFT-mediated emulsion polymerization to fabricate monodisperse colloidal nanospheres of poly(acrylic acid)ₙ-block-polystyrene (PAAₙ-b-PS), respectively. Due to the uniform carboxyl groups on the surface, the resulting nanospheres exhibited high surface charge (ζ-potential = -50 to -60 mV) and excellent steric stability. By carefully adjusting key parameters, such as the system's pH and the length of the PAAn chains, Self-assembly of the colloidal nanospheres into LPCs was achieved by rotary evaporation. These LPCs achieved a solid content of up to 55 wt% and displayed bright structural colors without requiring extra stabilizers. Notably, the LPCs showed outstanding dynamic recovery. After mechanical disruption, they quickly and autonomously regained their ordered structure and structural color. We also conducted preliminary tests to explore the potential use of these LPCs in pH-responsive hydrogel materials. This work offers a reliable approach for synthesizing, assembling, and scaling up production of highly stable and functional LPCs materials.