Light-Driven Spatiotemporal Pickering Emulsion Droplet Manipulation Enabled by Plasmonic Hybrid Microgels

The past decades have witnessed the development of various stimuli-responsive materials with tailored functionalities, enabling droplet manipulation through external force fields. Among different strategies, light exhibits excellent flexibility for contactless control of droplets, particularly in three-dimensional space. Here, we present a facile synthesis of plasmonic hybrid microgels based on the electrostatic heterocoagulation between cationic microgels and anionic Au nanoparticles. The hybrid microgels are effective stabilizers of oil-in-water Pickering emulsions. In addition, the laser irradiation on Au nanoparticles creats a cascade effect to thermally responsive microgels, which triggers a change in microgel wettability, resulting in microgel desorption and emulsion destabilization. More importantly, the localized heating generated by a focused laser induces the generation of a vapor bubble inside oil droplets, leading to the formation of a novel air-in-oil-in-water (A/O/W) emulsion. These A/O/W droplets are able to mimic natural microswimmers in an aqueous environment by tracking the motion of a laser spot, thus achieving on-demand droplet merging and chemical communication between isolated droplets. Such proposed systems are expected to extend the applications of microgel-stabilized Pickering emulsions for substance transport, programmed release and controlled catalytic reactions.

Automated summary

In the past decades, various stimuli-responsive materials have been developed for droplet manipulation, with light being a flexible option for contactless control in three-dimensional space. This study presents a synthesis of plasmonic hybrid microgels through electrostatic heterocoagulation, which are effective stabilizers of oil-in-water Pickering emulsions. Laser irradiation on Au nanoparticles induces a cascade effect to thermally responsive microgels, causing microgel desorption and emulsion destabilization. The localized heating from a focused laser leads to the formation of air-in-oil-in-water emulsions, capable of mimicking natural microswimmers and achieving on-demand droplet merging and chemical communication.