SOLVATION EFFECT OF POLY(VINYL ALCOHOL) IN AQUEOUS SOLUTION via REPEATING FREEZING-THAWING CYCLES
聚乙烯醇水溶液反复冷冻过程中的溶剂化效应

The article is devoted to the study on solvation effect of poly(vinyl alcohol) (PVA) in aqueous solution via repeating freezing-thawing cycles using differential scanning calorimetry (DSC) technique.A straightforward method for determination of the hydration number,a parameter characterizing the extent of solvation effect,of polymers in aqueous solutions based on ice-melting technique of DSC is proposed.The simple yet precise method has been applied to determine the hydration number of PVA in aqueous solution covering a wide range of concentrations,from 0.005 to 0.3 g/g.The results indicate that the melting enthalpies and hydration numbers of PVA aqueous solutions differentiate greatly at different concentration regimes,i.e.dilute,semi-dilute,concentrated concentration region,which is attributed to the differences of intra-and inter-chain entanglements in their influence on the participation of solvent molecules in the solvation-desolvation process.The inter-chain entanglement points increase with increasing freezing cycles,which leads to part of solvent molecules entrapped in loops produced by inter-chain contact and forming a portion of polymer chain.Apparent change of solvation effect is a complex influence of desolvation and entrapped solvents.