Phase Separation Behavior of Aqueous Poly(N-isopropylacrylamide)Solutions Studied by Scattering Experiments

We have investigated the colloidal phase-separating dilute solution of aqueous poly(N-isopropylacrylamide) (PNIPAM)with a molecular weight of 1.24x105by small-angle X-rayscattering (SAXS) as well as static and dynamic light scattering (SLSand DLS). Those scattering experiments provide us with the averagesize and size distribution of concentrated-phase droplets and theconcentrationcconcof the coexisting concentrated phase. While theaverage droplet size is almost constant above 35 degrees C in thetemperature-scan experiments, it is a decreasing function oftemperature above 35 degrees C in the temperature-jump experiments.This heating rate dependence of the average droplet size arises fromthe fact that concentrated-phase droplets in the aqueous PNIPAMsolution grow only in a limited temperature range (31.5-35 degrees C).The scattering results on the temperature dependence ofcconcarecombined with previously reported results of turbidity and DSC,giving the phase diagram of the Type II phase behavior with the off-zero critical point at high molecular weight