Synthesis and characterization of self-oscillating P(AA-co-AM)/PEG semi-IPN hydrogels based on a pH oscillator in closed system

Various semi-interpenetrating polymer network (semi-IPN) hydrogels composed of pore-forming agent polyethylene glycol (PEG), acrylic acid (AA) and acrylamide (AM) were prepared by using free radical polymerization with a two-step method. The chemical structures of the synthesized hydrogels were characterized by FTIR spectroscopy and the morphologies were studied by scanning electron microscopy (SEM) method. The swelling properties, such as the pH-responsive behavior, salt sensitivity, oscillatory swelling/de-swelling behaviors in different solutions with various pH values and self-oscillating behaviors in bath pH oscillator were investigated in detail. The results revealed that the prepared hydrogels exhibited high pH sensitivity and excellent salt sensitivity when the pH values of the medium changes from 3.0 and 7.0 and well reversible properties by undergoing a number of swelling/de-swelling recycles. In particular, the hydrogels exhibited self-oscillation behavior in a closed system containing BrO3 -SO3 Fe2-(CN)(6) H-4-(+). This study may create a new possibility as biomaterial for new self-walking actuators and other devices.