Preparation, Characterization, and swelling study of N,N’-dimethylacrylamide/acrylic acid amphiphilic hydrogels in different conditions

This research was an attempt to synthesize a series of amphiphilic hydrogels based on different molar ratios of N,N-dimethylacrylamide (DMAM) and acrylic acid (AA) and investigated the influence of pH, time, temperature, and salinity of water on the swelling behavior of the hydrogels. The swelling kinetic parameters and swelling diffusion were also determined. The synthesis of DMAM/AA hydrogel using N,N'-methylenebisacrylamide as a cross-linking agent and AIBN as initiator was confirmed by Fourier transform infrared spectroscopy (FTIR). The swelling results revealed that the hydrogel swelling reduced as a content of AA. Also, it was demonstrated that increasing the pH caused a drastic increment of the equilibrium swelling ratio and the maximum extent (5150%) was reached at pH 14 for sample AHD3 containing 25% AA. The swelling mechanism study showed that for all samples, Fickian diffusion was responsible for water transport as well as the swelling process was considerably influenced by the chemical structure of the monomer repeating units in the synthesized samples. The swelling study of the hydrogel in the aqueous solution of NaCl and Na2SO4 showed that increasing the salt concentration caused in limitation of water absorption. Also, the swelling degree in the aqueous solution of Na2So4 was slightly higher than NaCl. It was also shown that the increase in temperature of the swelling process led to enhancement of swelling ratio in distilled water.