Stimuli response of polysoap hydrogels in aqueous solution and DC electric fields

Novel types of polysoap hydrogels based on hydrophobically-modified polyelectrolytes crosslinked with N,N-methylenebisacrylamide have been prepared by free radical polymerization at 70–80°C in aqueous solution with ammonium persulfate as initiator. Poly(diallylamine-co-N,N-dodecylmethyldiallylammonium bromide) (PDA-C12), poly(N-methyldiallyl-co-N,N-dodecylmethyldiallylammonium bromide) (PMDA-C12) both contain hydrophobic side chains with 12 carbon atoms. The swelling behavior of these polysoap hydrogels was studied by immersion of the gels in buffered solutions at various pHs and ionic strengths. It was found that the structure of the polysoap backbone influenced the pH-dependent swelling and deswelling. The swelling process is reversible after repeating cycles of swelling and deswelling induced by a change of pH in appropriate buffer solutions. SEM micrographs of polysoap gels indicate that the network structures are characterized by the presence of large open pores or small closed pores. The stimuli response of the polysoap gels in electric fields was also investigated. In a contact electric field, deswelling was observed at the anode side of the gels. In a non-contact electric field, the gels bend towards the anode. The gels can turn back to the original shape and bend toward the cathode with time when higher electric potentials are applied. These properties of the gels are related to both the change of osmotic pressure caused by mobile ions and by hydrophobic interactions.