Adjacent UCST Phase Behavior in Aqueous Solutions of Poly(vinyl methyl ether): Detection of a Narrow Low Temperature UCST in the Lower Concentration Range
Van Assche, Guy Van Mele, Bruno Li, Ting × Nies, Eric #
American Chemical Society
Macromolecules vol:44 issue:4 pages:993-998
We provide the first experimental evidence for the existence of a low concentration narrow UCST miscibility gap, which is the second of two narrow miscibility gaps constituting together adjacent UCST phase behavior. The existence of adjacent UCST miscibility phase behavior in aqueous polymer solutions has been theoretically predicted, but so far escaped experimental verification. We have been able to determine the low concentration narrow UCST miscibility gaps from the changes in apparent heat capacity observed in stepwise isothermal cooling modulated temperature differential scanning calorimetry (MTDSC) experiments. In wide-angle X-ray diffraction (WAXD) experiments it was unambiguously demonstrated that the MTDSC heat capacity changes are not due to crystallization. Together with earlier experimental results on the high concentration narrow UCST miscibility gap, the bimodal LCST miscibility gap and the sigmoidal melting line of ice the experimental results reported in this work complete the full experimental verification of the predicted complex phase behavior of aqueous solutions of PVME. As far as the authors are aware, this is the first system where adjacent UCST phase behavior is found. On the basis of the theoretical predictions the observed phase behavior could be more general and other systems may exist where similar behavior can be observed.