Torres Miguel F, Müller Alejandro J, Szidarovszky Miklos A, Sáez A Eduardo
Grupo de Polímeros USB, Departamento de Ciencias de los Materiales, Universidad Simón Bolívar, Caracas 1080A, Venezuela.
J Colloid Interface Sci. 2008 Oct 1;326(1):254-60. doi: 10.1016/j.jcis.2008.07.032. Epub 2008 Jul 24.
Interactions between a high molecular weight poly(ethylene oxide) (PEO) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions were investigated by shear and extensional rheometry. Results for mixtures between PEO and sodium dodecyl sulfate (SDS) are also presented for comparison purposes. Addition of anionic surfactants to PEO solutions above the critical aggregation concentration (CAC), at which micellar aggregates attach to the polymer chain, results in an increase in shear viscosity due to PEO coil expansion, and a strengthening of interchain interactions. In extensional flows, these interactions result in a decrease of the critical shear rate for the onset of the characteristic extension thickening of the PEO solutions that is due to transient entanglements of polymer molecules. The relaxation times associated with these transient entanglements are not directly proportional to the shear viscosity of the solutions, but rather vary more rapidly with surfactant concentration. In the presence of an electrolyte, coil contraction results in lower shear viscosities and a decrease in the extension thickening effects at surfactant concentrations just beyond the CAC. The relaxation times associated with transient entanglement reach a minimum at the same surfactant concentration as the shear viscosity, which indicates that coil contraction is responsible for the observed effects in both types of flow. However, the increase in extensional-flow entanglement relaxation times is much more abrupt than the decrease in shear viscosity. All these results point to a greater sensitivity of extensional flows on the molecular conformation of PEO/surfactant complexes.
通过剪切流变仪和拉伸流变仪研究了高分子量聚环氧乙烷（PEO）与阴离子表面活性剂十二烷基苯磺酸钠（SDBS）在水溶液中的相互作用。为了进行比较，还给出了PEO与十二烷基硫酸钠（SDS）混合物的结果。在临界聚集浓度（CAC）以上向PEO溶液中添加阴离子表面活性剂，此时胶束聚集体附着在聚合物链上，由于PEO线团膨胀，剪切粘度增加，链间相互作用增强。在拉伸流动中，这些相互作用导致PEO溶液特征性拉伸增稠开始时的临界剪切速率降低，这是由于聚合物分子的瞬时缠结所致。与这些瞬时缠结相关的松弛时间与溶液的剪切粘度不成正比，而是随表面活性剂浓度变化得更快。在存在电解质的情况下，线团收缩导致较低的剪切粘度，并且在表面活性剂浓度刚刚超过CAC时拉伸增稠效应降低。与瞬时缠结相关的松弛时间在与剪切粘度相同的表面活性剂浓度下达到最小值，这表明线团收缩是两种流动类型中观察到的效应的原因。然而，拉伸流动缠结松弛时间的增加比剪切粘度的降低要突然得多。所有这些结果表明拉伸流动对PEO/表面活性剂复合物的分子构象更敏感。
