Hierarchical Assemblies of Bottlebrush/Homopolymer Blends: Tailoring Phase Interfacial Curvature for Tunable Photonics^†

Abstract

Organized spontaneous emulsification (OSE) produces ordered water-in-oil-in-water (W/O/W) multiple emulsion droplets stabilized by bottlebrush block copolymer (BBCP) surfactants, such as (polynorbornene-g-polystyrene)-b-(polynorbornene-g-polyethylene oxide) (PS-b-PEO), templating ordered porous particles with visible structural colors. Here, homopolymer polystyrenes (hPS) were used to swell the PS domain and thus to effectively increase the W/O interfacial curvature of the internal droplets. By variation of hPS concentration, pore diameter is largely tunable from 34 to over 210 nm, leading to tunable photonic bandgaps in the whole visible spectrum. The ratio (α) of molecular weight of hPS relative to that of the PS side chains of the BBCP can greatly influence their spatial distribution within the PS domain. For α ≤ 1, uniform solubilization of the hPS chains into the side chains of BBCP is achieved leading to a homogeneous porous structure. For α > 1, local solubilization of the hPS chains at interface of the internal droplets is disclosed at relatively low concentrations of hPS (≤ 42 wt%), resulting in a small change in pore diameter. For contrast, a rapid increase of the W/O interfacial curvature was observed upon further increase of the hPS content (> 42 wt%) through an evident influence on the OSE procedure.