Effect of organic anion with multiple hydrophobic sites on gelation and phase separation in aqueous methylcellulose solution: Beyond simple salting-in effect

Publication date: Available online 12 June 2019Source: PolymerAuthor(s): Motoki Shibata, Tsuyoshi Koga, Koji NishidaAbstractWe studied addition effect of sodium tetraphenylborate (NaBPh4), an organic salt with multiple hydrophobic sites, on thermoresponsive behavior of aqueous methylcellulose (MC) solution. By means of simultaneous measurements of viscosity and light transmittance during heating, it was clarified that the concentration of added NaBPh4 determines which of gelation and phase separation occurs first. Aqueous MC solution without NaBPh4 formed gels below the phase separation temperature, and therefore the phase separation remained incomplete. With increasing the concentration of added NaBPh4, the gelation temperature monotonously increased, whereas the phase separation exhibited complicated behavior. The phase separation temperature in gel phase drastically increased by addition of small amount of NaBPh4 in similar fashion to the gelation temperature, although the phase separation in gel phase faded away when the concentration of NaBPh4 exceeded ca. 0.05 M. Alternatively, liquid-liquid phase separation appeared. In contrast to the phase separation in gel phase, the liquid-liquid phase separation occurred essentially below the gelation temperature and proceeded completely to form macroscopic binary domains. Temperature of the liquid-liquid phase separation decreased initially, but it turned upward when the concentration of added NaBPh4 exceeded ca. 0.15 M and i...
Source: Polymer - Category: Chemistry Source Type: research