Interfacial Behavior of Microgels Revealed via Direct Visualization at Fluid Interfaces

Hydrogel microparticles, also known as microgels, are water-swollen colloidal particles with a structure comprising three-dimensionally crosslinked hydrated polymer chains. Owing to their hybrid characteristics of both hydrogels and colloidal particles, unlike rigid particles, microgels can instantly deform to cover and stabilize fluid interfaces, that is, air-water and oil-water interfaces upon adsorption. In this chapter, we describe our investigation of the adsorption, deformation, ordering, and transfer processes of microgels at the air–water interface during the drying of microgel dispersion droplets via direct visualization with a microscope. In addition, we summarize the development of diverse self-organized patterns of microgels during the evaporation of droplets containing new functional microgels and their application to the fabrication of microgel-stabilized emulsions and long-term-stable gel foams. Finally, we present recent insights and future directions on the compression behavior of microgels at the air–water interface revealed via direct visualization.