(713b) The Role of Hofmeister Series in Controlling Phase Transition Behavior of Surface-Tethered Polymer Networks

Lower critical solution temperature (LCST) polymers exhibit a reversible phase transition when subjected to small perturbations in external stimuli. We have synthesized a series of photo-cross-linkable co-polymers based on N-alkylacrylamides and methacroyloxy-benzophenone (MaBP). The swelling behavior of N-isopropylacrylamide, N-n-propylacryalmide and N-cyclopropylacrylamide based polymers having different permutations of hydrophilic/hydrophobic moieties were studied under the influence of different environmental cues like temperature and salts. Kosmotropic and chaotropic salts exhibit salting out and salting in behavior depending on their position in the Hofmeister series. Our results indicate that salts interact directly with the polymer groups either through direct interaction with the hydrophilic/hydrophobic groups or by polarization effect of water molecules. It is expected that by carefully elucidating different polymer structure and the effects of salts on their phase separation will guide us in establishing structure-property relationships for different polymer systems. To this effect, we have investigated N-alkylacrylamide based polymers using ellipsometry, FTIR, and QCM-D to better understand the role of salts on the phase transition behavior of these thermoresponsive polymers.