Mechanism-Selective Self-Assembly of Amphiphilic Dendronized Brush Block Copolymers Into Lamellar and Porous Photonic Pigments.

Abstract

Polymeric photonic microspheres with visible structural colors offer safe and vibrant alternatives to traditional toxic pigments. These materials are commonly fabricated through confined self-assembly of block copolymers (BCPs) in evaporative emulsions, which can proceed by either microphase separation or organized spontaneous emulsification (OSE) to yield lamellar or porous structures with complementary optical responses. In this study, we show that amphiphilic dendronized brush block copolymers (den-BBCPs) exhibit mechanism-selective self-assembly governed by the volume fraction (f) of hydrophilic segment. At f < 50%, den-BBCPs follow the OSE pathway, generating photonic microspheres with short-range-ordered porous structures and angle-independent structural colors. In contrast, at f > 50%, microphase separation dominates, producing concentric lamellar microspheres with strong specular reflections. This pathway transition arises from the rigid dendronized architecture: increasing the volume fraction of hydrophilic segment amplifies intermolecular repulsions at the highly curved water-in-oil nanodroplet interface, destabilizing interfacial association and redirecting assembly toward microphase separation. This work establishes architectural engineering of den-BBCPs as a powerful strategy for programming self-assembly pathways and creating polymeric photonic pigments with diverse structures and optical properties.