A self-templating dilution strategy for preparation of hollow concave polystyrene nanoparticles in a styrene/ethanol-water ternary system

Hollow concave polymer particles have attracted wide attention due to their particular properties and applications, however, the controllable synthesis of hollow concave polystyrene nanoparticles (HC-PSNPs) based on soap-free emulsion polymerization via a one-pot method has not been achieved. Herein, based on a styrene/ethanol-water (St/EtOH-H 2 O) ternary system, a simple green self-templating dilution strategy was established to produce monodisperse HC-PSNPs. In the synthesis, the degree of concavity and opening size of HC-PSNPs can be controlled by adjusting polymerization parameters such as the pre-polymerization time (polymerization time before dilution) and dilution conditions (including dilution ratio and ethanol content of the diluents). Furthermore, one opening or multiple openings in the surface of HC-PSNPs can be controlled by varying the post-polymerization temperature (polymerization temperature after dilution). Based on our results and observations, we propose a plausible mechanism for the formation of HC-PSNPs.