疏水缔合共聚物与表面活性剂的界面相互作用

采用界面张力弛豫法研究了疏水缔合聚合物聚丙烯酰胺/2-乙基己基丙烯酸酯P(AM/2-EHA)]在正辛烷-水界面上的扩张粘弹性质, 考察了不同类型表面活性剂十二烷基硫酸钠(SDS)、聚环氧乙烯醚(Tx-100)和十六烷基三甲基溴化铵(CTAB)对其界面扩张性质的影响. 研究发现, 界面上的表面活性剂分子可以与聚合物的疏水嵌段形成类似混合胶束的聚集体, 表面活性剂分子与聚集体之间存在快速交换. 这种弛豫过程的特征时间远比分子在体相与界面间的扩散交换时短. 当界面面积增大时, 上述混合胶束中的表面活性剂分子能快速释放, 在界面层内原位快速消除界面张力梯度, 从而大大降低界面扩张弹性. 界面上的CTAB分子与聚合物链节上的负电中心通过较强的电荷吸引作用形成复合物. 当界面面积增大时, 上述混合胶束中的CTAB分子释放较慢, 界面张力梯度较大. 非离子表面活性剂Tx-100分子量较大, 扩散速率较慢, 它在界面上与聚集体间的交换比阴离子表面活性剂SDS慢, 其特征时间约为0.9 s.

Study on Interfacial Interaction between Hydrophobically Modified Polyacrylamide and Surfactants

The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2-ethylhexyl acrylate (EHA) (＜ 1.0% mole fraction) with a hydrolysis degree of about 1.5%～2.0% at the octane-water interfaces were investigated by interfacial tension relaxation method. The influences of anionic surfactant sodium dodecyl sulfate (SDS), cationic surfactant cetyl trimethylammonium bromide (CTAB) and nonionic surfactant Triton X-100 on the dilational viscoelastic properties of 7 g?L-1 polymer solutions were studied. The results showed that surfactants can influence the dilational properties of polymer solutions by providing a new fast relaxation process involving the exchange of surfactant molecules between monomers and mixed micelles at interface. By adding SDS, this new process is so fast that its characteristic time can′t be obtained. However, for Triton X-100, which has a relative higher molecular weight, the characteristic time was about 0.9 s. By adding CTAB, the slow process changed obviously due to the strong electrostatic interaction between oppositely charged surfactant and hydrolyzed part of polymer chain.