Kuperkar K, Abezgauz L, Danino D, Verma G, Hassan P A, Aswal V K, Varade D, Bahadur P
Veer Narmad South Gujarat University, Surat, India.
J Colloid Interface Sci. 2008 Jul 15;323(2):403-9. doi: 10.1016/j.jcis.2008.04.040. Epub 2008 Apr 23.
Aqueous micellar solutions of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO(3)) were examined using steady and dynamic rheology, small-angle neutron scattering (SANS) and cryogenic-transmission electron microscopy (cryo-TEM). Upon addition of NaNO(3), the CTAB spherical micelles transform into long, flexible wormlike micelles, conveying viscoelastic properties to the solutions. The zero-shear viscosity (eta(0)) versus NaNO(3) concentration curve exhibits a well-defined maximum. Likewise, upon increase in temperature, the viscosity decreases. Dynamic rheological data of the entangled micellar solutions can be well described by the Maxwell model. Changes in the structural parameters of the micelles with addition of NaNO(3) were inferred from SANS measurements. The intensity of scattered neutrons at the low q region was found to increase with increasing NaNO(3) concentration. This suggests an increase in size of the micelles and/or decrease of intermicellar interactions with increasing salt concentration. Analysis of the SANS data using prolate ellipsoidal structure and Yukawa form of interaction potential between micelles indicates that addition of NaNO(3) leads to a decrease in the surface charge of the ellipsoidal micelles and consequently an increase in their length. The structural transition from spherical to entangled threadlike micelles, induced by the addition of NaNO(3) to CTAB micelles is further confirmed by cryo-TEM.
使用稳态和动态流变学、小角中子散射（SANS）和低温透射电子显微镜（cryo-TEM）对阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）和硝酸钠（NaNO₃）的水相胶束溶液进行了研究。加入NaNO₃后，CTAB球形胶束转变为长的、柔性的蠕虫状胶束，赋予溶液粘弹性。零剪切粘度（η₀）与NaNO₃浓度曲线呈现出明确的最大值。同样，随着温度升高，粘度降低。缠结胶束溶液的动态流变数据可以用麦克斯韦模型很好地描述。通过SANS测量推断出加入NaNO₃后胶束结构参数的变化。发现低q区域的散射中子强度随着NaNO₃浓度的增加而增加。这表明随着盐浓度的增加，胶束尺寸增大和/或胶束间相互作用减小。使用长椭球体结构和胶束间相互作用势的汤川形式对SANS数据进行分析表明，加入NaNO₃会导致椭球形胶束表面电荷减少，从而使其长度增加。cryo-TEM进一步证实了向CTAB胶束中加入NaNO₃所诱导的从球形到缠结丝状胶束的结构转变。
