Spontaneous self-organization to form complex structures in nature is an inspiration for designing new engineering materials for diverse applications. Recently, anisotropic colloidal particles were self-assembled into a highly ordered crystalline colloidal array (CCA). This has tremendous potential as a photonic crystal (PC). This work describes a simple and facile strategy to achieve salt-responsive photonic crystal (PC) through self-assembly using zwitterionic functionalized microsphere with tunable morphologies.<br/>Monodisperse non-spherical polymer particles (NSP) with different sizes were prepared through a one-pot surfactant free-emulsion copolymerization technique. The highly charged latex particles consist of cationic ammonium and anionic sulfonate groups at the surface with polystyrene as a core. The phase-separated NSP with different morphologies such as the sphere, quasi-sphere, bulge, eyeball, and snowman were obtained on controlling the aqueous emulsion polymerization process. The monodisperse NSP colloids were employed to fabricate a robust 3D-ordered CCA through a bottom-up self-assembly process. The evaporation-driven self-assembly facilitates Bragg diffraction in the UV/Visible spectral region, leading to tunable iridescent polymer opals. Upon treatment with different salt concentrations, the rigid and highly stable polymer particles serve as an excellent salt-responsive PC through unique “anti-polyelectrolyte” behavior.

Salt-responsive photonic crystal from monodisperse zwitterionic microspheres

ACS Fall 2021

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