Slow crystallization kinetics of poly(vinyl alcohol) in confined environment during cryotropic gelation of aqueous solutions

The gelation kinetics of aqueous solutions of poly(vinyl alcohol) (PVA) during freezing at -13 degrees C has been investigated with time-resolved small angle neutron scattering. Crystallization of PVA takes place inside an unfrozen liquid microphase that forms in the matrix of ice crystals and follows a first-order kinetics during the early stages and becomes very slow in the later stages with an apparent Avrami exponent lower than 1. Crystallization of PVA at low temperatures is responsible of formation of strong physical gels upon defrosting, provided that the concentration of PVA is higher than a critical value.