Swelling behavior of polyelectrolyte gels in the presence of salts

The swelling behavior of weakly crosslinked polyelectrolyte gels based on s odium methacrylate (PMA) and diallyldimethylammonium chloride (DADMAC) in a queous medium was studied in the presence of different types of salts (NaCl , arginine hydrochloride, cetylpyridinium chloride (CPC), sodium dodecyl su lfate (SDS), and sodium dodecylbenzenesulfonate (SDBS)). It is shown that, starting from some characteristic concentration of a salt, a further increa se of the salt concentration results in the shrinking of the gels. This cha racteristic concentration is defined by the gel parameters (polymer concent ration in the gel that is a function of the monomer concentration at the co nditions of hydrogel synthesis) and does not depend on the kind of salt use d, except for the system polyelectrolyte gel/oppositely charged surfactant (PMA-CPC and DADMAC-SDS or SDBS). It is shown that the initial rate of gel shrinking for all studied systems, including the system gel/oppositely char ged surfactant, is determined by the salt concentration and the gel paramet ers. For the systems PMA-CPC and DADMAC-SDS the gel collapse is a two-step process.