十二烷基硫酸钠对聚乙烯醇亚浓水溶液流变行为的影响

表面活性剂会影响聚乙烯醇(PVA)分子间及分子内氢键形成,进而改变其水溶液的流变响应.本文在确定十二烷基硫酸钠(SDS)在PVA亚浓水溶液中的临界聚集浓度(CAC)和临界胶束浓度(CMCP)基础上,考察了SDS对PVA亚浓溶液(10 wt%)流变行为的影响.研究发现,不同浓度SDScsur对PVA水溶液稳态流变行为的影响差异较大:(1)当csur CMCP,随着csur增加,胶束起物理交联点作用,ηa增大,复合溶液的动态储能模量亦显著增大.加入SDS后,PVA体系内结合水的数目降低,但当csur> CMC后,结合水的数目几乎不变,黏流活化能也表现出相近的变化规律.与稀溶液相比,SDS对PVA亚浓溶液的降黏幅度较大.     

Tough polyion complex hydrogel films of natural polysaccharides

The developments of tough hydrogels in recent years have greatly expanded the applications of hydrogels as structural materials. However, most of the tough hydrogels are made of synthetic polymers. To develop biopolymer-based tough hydrogels has both fundamental and practical significances. Here we report a series of polysaccharides-based tough hydrogel films prepared by polyion complexation and solvent evaporation of chondroitin sulfate(CS) and protonated chitosan(CHT) solutions with different weight ratios. The obtained CS/CHT gel films with thickness of 40-80 μm and water content of 66 wt%-81 wt% possess excellent mechanical properties, with tensile breaking stress and breaking strain being 0.4-3 MPa and 160%-320%, respectively. We found that in the mixture solutions there are large amounts of excess CHT in terms of charges; after swelling the films in water, the acetic acid, which is used to protonate the amino groups of CHT, diffuses out of the gel matrix, enhancing the intermolecular interactions between CHT molecules and thus improving the mechanical properties of gel films, besides the ionic bonds between CS and CHT. Antimicrobial tests also showed that the gel films with low weight ratio of CS to CHT, corresponding to the case with excess CHT, have evident antimicrobial effect. These CS/CHT gel films with good mechanical properties and antimicrobial effect should extend the applications of hydrogels in biomedical fields.     

一维粒子对聚乙烯醇水溶液流变行为的调控

将一维粒子(碳纳米管, CNTs; 碳纳米纤维, CF)加入聚乙烯醇(PVA)水溶液中, 考察碳粒子表面含氧官能团含量(羟值)、 长径比、 温度及PVA本体溶液浓度等对复合体系流变行为的影响. 结果显示, 复合溶液的黏度(η)随CNTs用量({\phi }_{\mathrm{C}\mathrm{N}\mathrm{T}\mathrm{s}})先增大后降低, 然后继续增大, 呈“N”形变化趋势, 出现两个拐点({\phi }_{\mathrm{1}}和{\phi }_{\mathrm{2}}). 在{\phi }_{\mathrm{1}}附近, CNTs主要起物理交联点作用, 体系η增加; 在{\phi }_{\mathrm{2}}附近, CNTs对PVA分子间氢键作用破坏最为严重, 体系η低于纯PVA溶液, 表明不同羟值CNTs仅改变其用量即可使PVA水溶液增黏或降黏. 随着羟值增大, CNTs与PVA大分子间相互作用加强, {\phi }_{\mathrm{1}}和{\phi }_{\mathrm{2}}减小, {\phi }_{\mathrm{2}}对应的η下降, 降黏效果显著. CNTs的加入使PVA水合数下降, 羟值大的CNTs可与PVA上更多的羟基形成氢键作用, 水合数更低. 随着{\phi }_{\mathrm{C}\mathrm{N}\mathrm{T}\mathrm{s}}增大, 复合体系黏流活化能增大. CNTs对不同质量分数PVA水溶液的η具有类似的调控作用, 但调控幅度有差异. 相同羟值、 不同长径比的CNTs对PVA水溶液的黏度调控均呈“N”形变化, 长径比小的CNTs复合体系, {\phi }_{\mathrm{1}}和{\phi }_{\mathrm{2}}较大. 长径比相近但直径较大的CF复合体系表现出更低的{\phi }_{\mathrm{1}}和{\phi }_{\mathrm{2}}.