Effects of Hofmeister Anions on the LCST of PNIPAM as a Function of Molecular Weight

作者：Yanjie Zhang, Steven Furyk, Laura B. Sagle, Younhee Cho, David E. Bergbreiter, Paul S. Cremer · 发表于：The Journal of Physical Chemistry C · 年份：2007 · DOI：10.1021/jp0690603 · 被引用次数：405 · 研究领域：Spectroscopy and Quantum Chemical Studies、Analytical Chemistry and Sensors、Microfluidic and Capillary Electrophoresis Applications

The effect of a series of sodium salts on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide), PNIPAM, was investigated as a function of molecular weight and polymer concentration with a temperature gradient microfluidic device under a dark-field microscope. In solutions containing sufficient concentrations of kosmotropic anions, the phase transition of PNIPAM was resolved into two separate steps for higher molecular weight samples. The first step of this two step transition was found to be sensitive to the polymer's molecular weight and solution concentration, while the second step was not. Moreover, the binding of chaotropic anions to the polymer was also influenced by molecular weight. Both sets of results could be explained by the formation of intramolecular and intermolecular hydrogen-bonding between polymer chains. By contrast, the hydrophobic hydration of the isopropyl moieties and polymer backbone was found to be unaffected by either the polymer's molecular weight or solution concentration.