聚乙烯醇水溶液反复冷冻过程中的溶剂化效应

采用示差扫描量热技术(DSC)对聚乙烯醇(PVA)水溶液反复冰冻过程中的溶剂化效应进行研究.引入水化数的概念来表征溶剂化效应的大小.结果表明不同浓度区间的PVA水溶液其在反复冰冻过程中溶剂化效应显著不同,主要归因于高分子链分子内和分子间缠结程度对溶剂分子"参与"溶剂化的程度和方式的不同.作者把极稀高分子溶液的研究结果拓展到高分子稀溶液或亚浓溶液区间,阐述了高分子溶液中高分子链的物理图像.冷冻次数的增加导致链间缠结增加,部分溶剂则被包裹在由链间缠结点所形成的网圈内成为分子链的一部分.溶液溶剂化程度的变化受到包裹溶剂与高分子链脱溶剂化的综合影响.

SOLVATION EFFECT OF POLY(VINYL ALCOHOL) IN AQUEOUS SOLUTION via REPEATING FREEZING-THAWING CYCLES

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.