氢键作用对聚乙烯醇水溶液流变行为的影响

Influence of Hydrogen-bond on the Rheological Behavior of Poly(vinyl alcohol)

聚乙烯醇(PVA)水溶液的流变行为不同于一般高分子溶液,与其体系内分子间氢键相互作用密切相关.流变测试结果表明,其稳态流变曲线可分为4个区域,即第一平台区、第一剪切变稀区、第二平台区和第二剪切变稀区.结合理论分析确定第一平台区及第一剪切变稀区与分子间氢键形成的网络结构有关,而第二剪切变稀区与PVA大分子链的解交叠有关.此外,醇解度、剪切历史、静置时间等因素均可改变PVA分子间氢键相互作用,进而影响其流变行为.

Different from general polymer solutions, poly （vinyl alcohol） （PVA） aqueous solutions showed distinctive rheological behaviors caused by the hydrogen bonded networks, which include hydrogen bonding between polymer chains and water,intra and inter macromolecular hydrogen bonding. The steady shear curves sol PVA aqueous solutions with the concentration of 10 wt% indicated four regions with increasing shear rate, the first plateau, the first shear thinning region, the second plateau and the second shear thinning region. The experimental results combined with the scaling theory exhibited that the occurrence of the first shear thinning region owed to the inter-macromolecular hydrogen bonding while the arising of the second shear thinning region was due to the disentanglement of PVA chains. The decreasing of viscosity and hydration number of PVA aqueous solutions with introduction of sodium dodecyl sulfate （SDS） also demonstrated the rheologieal behavior of PVA aqueous solutions in low shear range mainly depended upon the inter-macromolecular hydrogen bonding. In addition,changes in alcoholysis degree and shearing history produced remarkable effect on hydrogen bonded networks, making different rheological responds for PVA aqueous solutions. Since PVA is a semi-crystalline polymer, spinodal decomposition could be observed in PVA aqueous solutions,resulting in the appearance of polymer-rich and polymer-poor phases. The longer aging time benefited the formation of hydrogen bonding and the phase separation of PVA aqueous solutions, causing the increase of viscosity during the shear recovery process upon decreasing shear rate.