Aqueous mixtures of anionic and nonionic/cationic surfactants can form non-trivial self-assemblies in solution and exhibit macroscopic responses. Here, we investigate the micellar phase of pure and mixed aqueous solutions of Sodium Dodecyl Sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO) using a combination of Small Angle Neutron Scattering (SANS), Fourier-Transform Infrared Spectroscopy (FTIR) and rheological measurements. We examine the effect of temperature (0–60 °C), on the 20 wt% SDS micellar solutions with varying DDAO ($⩽$5 wt%), and seek to correlate micellar structure with zero-shear solution viscosity. SANS establishes the formation of prolate ellipsoidal micelles in aqueous solutions of pure SDS, DDAO and SDS/DDAO mixtures, whose axial ratio is found to increase upon cooling. Elongation of the ellipsoidal micelles of pure SDS is also induced by the introduction of the non-anionic DDAO, which effectively reduces the repulsive interactions between the anionic SDS head-groups. In FTIR measurements, the formation of elongated mixed ellipsoidal micelles is confirmed by the increase of ordering in the hydrocarbon chain tails and interaction between surfactant head-groups. We find that the zero-shear viscosity of the mixed surfactant solutions increases exponentially with decreasing temperature and increasing DDAO content. Significantly, a master curve for solution viscosity can be obtained in terms of micellar aspect ratio, subsuming the effects of both temperature and DDAO composition in the experimental range investigated. The intrinsic viscosity of mixed micellar solutions is significantly larger than the analytical and numerical predictions for Brownian suspensions of ellipsoidal colloids, highlighting the need to consider interactions of soft micelles under shear, especially at high concentrations.

阴离子和非离子/阳离子表面活性剂的水性混合物可在溶液中形成非平凡的自组装，并表现出宏观响应。在这里，我们使用小角度中子散射（SANS），傅里叶变换红外光谱（FTIR）和流变学测量方法研究十二烷基硫酸钠（SDS）和二甲基十二烷基氧化胺（DDAO）的纯水溶液和混合水溶液的胶束相。我们研究了温度（0–60°C）对20重量％SDS胶束溶液的DDAO变化的影响（$⩽$5 wt％），并寻求使胶束结构与零剪切溶液粘度相关联。SANS在纯SDS，DDAO和SDS / DDAO混合物的水溶液中建立了椭圆形长胶束的形成，发现其轴比随冷却而增加。通过引入非阴离子DDAO，还可以诱导纯SDS的椭球胶束的伸长，这有效地减少了阴离子SDS头基之间的排斥相互作用。在FTIR测量中，烃链尾部的有序化和表面活性剂头基之间的相互作用增加，从而证实了细长混合椭球胶束的形成。我们发现，混合表面活性剂溶液的零剪切粘度随着温度的降低和DDAO含量的增加而呈指数增长。重要的是 假设温度和DDAO组成均在所研究的实验范围内，则可以根据胶束长宽比获得溶液粘度的主曲线。混合胶束溶液的特性粘度明显大于椭圆形胶体布朗悬浮液的分析和数值预测，这突出表明需要考虑软胶束在剪切作用下，特别是在高浓度下的相互作用。