Acharya Durga P, Sharma Suraj Chandra, Rodriguez-Abreu Carlos, Aramaki Kenji
Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
J Phys Chem B. 2006 Oct 19;110(41):20224-34. doi: 10.1021/jp063804v.
The formation and rheological behavior of a viscoelastic wormlike micellar solution in an aqueous solution of a nonionic fluorinated surfactant, perfluoroalkyl sulfonamide ethoxylate, of structure C8F17SO2N(C3H7)(CH2CH2O)10H was studied. Temperature-induced viscosity growth is observed even at low-surfactant concentration (approximately 1 wt %), and viscosity reaches the maximum at a temperature T(eta)-max. Upon successive increases in the temperature, the viscosity decreases, and ultimately a phase separation occurs. Small-angle X-ray scattering (SAXS) measurements confirm the presence of cylindrical aggregates at low temperature, which undergo continuous one-dimensional growth with increasing temperature, and ultimately, an indication of a slight lamellarlike structural pattern is observed, which probably comes from the formation of micellar joints or branching. Such changes in the microstructure result in a decrease in the viscosity and stress-relaxation time, while the network structure is retained; the trends in the evolution of shear modulus (Go) and relaxation time (tauR) with temperature are in agreement with this. With increased surfactant concentration, the temperature corresponding to the viscosity maximum (T eta-max) in the temperature-viscosity curve shifts to lower values, and the viscosity at temperatures below or around T eta-max increases sharply. A viscoelastic solution with Maxwellian-type dynamic rheological behavior at low-shear frequency is formed, which is typical of entangled wormlike micelles. Rheological parameters, eta(o) and Go, show scaling relationships with the surfactant concentrations with exponents slightly greater than the values predicted by the living-polymer model, but the exponent of tauR is in agreement with the theory. Dynamic light-scattering measurements indicate the presence of fast relaxation modes, associated with micelles, and medium and slow modes, associated with transient networks. The disappearance of the slow mode and the predominance of the medium mode as the temperature increases support the conclusions derived from SAXS and rheometry.
研究了结构为C8F17SO2N(C3H7)(CH2CH2O)10H的非离子型氟化表面活性剂全氟烷基磺酰胺乙氧基化物水溶液中粘弹性蠕虫状胶束溶液的形成及流变行为。即使在低表面活性剂浓度（约1 wt%）下也观察到温度诱导的粘度增长，且粘度在温度T(eta)-max时达到最大值。随着温度连续升高，粘度降低，最终发生相分离。小角X射线散射（SAXS）测量证实低温下存在圆柱形聚集体，其随温度升高经历连续的一维生长，并最终观察到轻微的层状结构模式迹象，这可能源于胶束接头或分支的形成。微观结构的这种变化导致粘度和应力松弛时间降低，同时网络结构得以保留；剪切模量（Go）和松弛时间（tauR）随温度的演变趋势与此一致。随着表面活性剂浓度增加，温度-粘度曲线中对应粘度最大值的温度（T eta-max）向较低值移动，且在低于或约等于T eta-max的温度下粘度急剧增加。形成了在低剪切频率下具有麦克斯韦型动态流变行为的粘弹性溶液，这是缠结蠕虫状胶束的典型特征。流变参数eta(o)和Go与表面活性剂浓度呈现标度关系，指数略大于活性聚合物模型预测的值，但tauR的指数与理论一致。动态光散射测量表明存在与胶束相关的快速弛豫模式以及与瞬态网络相关的中速和慢速模式。随着温度升高慢速模式的消失和中速模式的主导支持了从SAXS和流变测量得出的结论。
