Formation of Mesoglobules and Phase Separation at Variable Pressure in Aqueous Poly(N-isopropylacrylamide) Solutions Probed with Very Small-Angle Neutron Scattering

Thermoresponsive polymers featuring lower critical solution temperature (LCST) behavior in aqueous solution may serve as simple model system to investigate the effect of pressure on hydration and mesoscopic rearrangement during phase separation. We present structural studies of the size and water-content of the mesoglobules formed in a semidilute aqueous solution of Poly(N-isopropylacrylamide) (PNIPAM) in dependence on pressure at temperatures above the coexistence line. To characterize the large sizes of the mesoglobules as well as their water content, we use very small-angle neutron scattering (VSANS). The transition behavior between small mesoglobules (sub-micron) observed in semidilute PNIPAM solutions at low pressure and the large micron-scale aggregates at high pressure is investigated along various pathways in the pressure-temperature plane.