Low-Temperature Behaviors, Cold Crystallization, and Glass Transition in Poly(vinylpyrrolidone) Aqueous Solution

Intermediate water is a kind of water around the biocompatible polymer, such as poly-(vinylpyrrolidone) (PVP), that exhibits the phenomenon of cold crystallization. We investigate the low-temperature behavior of PVP aqueous solution using small- and wide-angle X-ray scattering and total neutron scattering measurements. The ice formation speed of the intermediate water is extremely reduced by confinement in the PVP moiety during the cooling process. However, around the glass transition temperature, the water-rich phase expands and orders the hydrogen-bond network, behaving as ice nuclei. During the heating process, cubic ice is formed first and then fills the water-rich region. After saturation of the cubic ice formation, the ice transforms from the cubic to the hexagonal ice form.