Floating Hydrogel Beads Made by Droplet Impact

Abstract Droplet impact is a ubiquitous natural phenomenon that has been widely utilized to inspire and facilitate many industrial applications. Compared to the widely studied water droplet impact onto identical liquid surfaces, the water droplet impact onto an oil layer floating on a water bath (OLW) receives far less attention and its potential application has never been exploited. Herein, the process of water droplet impact onto the OLW is investigated with emphasis on the metastable states and potential applications. It is found that the dramatic deformation of the oil–water interface caused by the water droplet impact leads to two metastable states: oil in water in oil in water (O/W/O/W) and oil in water in oil (O/W/O). Through the subsequent introduction of gelation process, the metastable states can be frozen into floating hydrogel beads with similar shape to the roly‐poly toys, which are attempted in gastric retentive drug delivery and algae bloom control. Specifically, the floating hydrogel beads perform well in gastric retentive drug delivery in vitro due to their inherent slow‐release properties and floating capability. In addition, the floating hydrogel beads loading photocatalysts can capture more sunshine, and exhibit high photocatalytic efficiency, which is thus responsible for efficient algae bloom control.