Interfacial Electrokinetic Phenomena of Thermoresponsive Microgels with a Spatial Gradient of Charged Groups

When functional microgels are synthesized via radical copolymerization, spatial gradients of functional groups often form due to a difference in reactivity ratios between monomer and comonomer. In this study, we systematically investigated the effect of a decreasing gradient of charged groups from the core to the shell of microgels on their surface properties, which are crucial for colloidal particles, through the analysis of interfacial electrokinetic phenomena using Ohshima's equation. A series of electrophoretic analyses combined with dynamic light scattering revealed that the surface of the microgels undergoes a multistep collapse during the particle-size reduction due to dehydration upon increasing the temperature. Furthermore, the more complicated hierarchical gradient of charged groups within the microgels was elucidated by quantitatively evaluating changes in surface properties during precipitation polymerization based on interfacial electrokinetic phenomena.