Lu Hongsheng, Shi Qianping, Huang Zhiyu
School of Chemistry and Chemical Engineering, Southwest Petroleum University , Xindu, Sichuan 610500, P. R. China.
J Phys Chem B. 2014 Oct 30;118(43):12511-7. doi: 10.1021/jp506809m. Epub 2014 Oct 22.
A pH-responsive anionic surfactant wormlike micellar system induced by NaCl has been developed. In this work, the anionic surfactant, sodium oleate (NaOA) solutions, transforms from low-viscosity fluid into high-viscoelastic solution induced by NaCl of 200 mM to 350 mM concentration. According to the above, the solution reversibility has been studied via changing pH value of the solution. This pH-responsive solution can be promptly switched between gel-like solution and waterlike fluid in a narrow pH value range. Steady and dynamic rheological measurements are employed to characterize the pH-responsiveness at different pH. The transformation between wormlike micelle and spherical micelle in the various pH solutions is demonstrated by dynamic light scattering tests, cryo-TEM, and NMR measurements. The pH-responsive property of the system is attributed to the carboxylate ion contained by sodium oleate. With higher pH value, the ionized carboxylate combines with NaCl closely and thus forms wormlike micelles. On the contrary, sodium oleate converts to oleate acid when pH decreases. In this way, spherical micelles are transformed because of the weaker interaction between oleate aicd and NaCl.
一种由氯化钠诱导的pH响应性阴离子表面活性剂蠕虫状胶束体系已被开发出来。在这项工作中，阴离子表面活性剂油酸钠（NaOA）溶液在200 mM至350 mM浓度的氯化钠作用下，从低粘度流体转变为高粘弹性溶液。据此，通过改变溶液的pH值研究了溶液的可逆性。这种pH响应性溶液可在狭窄的pH值范围内迅速在凝胶状溶液和水样流体之间切换。采用稳态和动态流变测量来表征不同pH值下的pH响应性。通过动态光散射测试、低温透射电子显微镜和核磁共振测量证明了在不同pH值溶液中蠕虫状胶束和球形胶束之间的转变。该体系的pH响应特性归因于油酸钠所含的羧酸根离子。随着pH值升高，电离的羧酸根与氯化钠紧密结合从而形成蠕虫状胶束。相反，当pH降低时，油酸钠转化为油酸。这样，由于油酸与氯化钠之间的相互作用较弱，球形胶束发生转变。
