pH Dependent swelling behavior of poly(2-hydroxyethyl methacrylate)-based copolymer hydrogels

A hydrogel is a highly hydrated polymer network which can be used as a sensor and an actuator due to its different swelling behavior responsive to external stimuli. In this report, we discuss the pH-dependent swelling behavior of PHEMA-based copolymer hydrogels. The swelling behavior of the PHEMA homopolymer hydrogel has little pH dependency. However, when the PHEMA is copolymerized with acrylic acid, the copolymer swells more at high pH condition. When dimethyl amine functional groups are introduced to the PHEMA hydrogel, the copolymer shows the opposite swelling behavior, i.e. higher swelling ratio at lower pH condition. Thus, the swelling behavior of the PHEMA-based hydrogel can be controlled by introducing different functional groups. Furthermore, we investigate the effect of initiator and crosslinker compositions on the swelling ratio of the hydrogel, to achieve more drastic pH-dependent swelling behavior. This study would provide helpful information for hydrogel-based applications, such as sensors and actuators.