Rastogi Preetika, Honecker Dirk, Alba Venero Diego, Mahmoudi Najet, Kaisare Niket S, Basavaraj Madivala G
Department of Chemical Engineering, Indian Institute of Technology, Madras, Chennai 600036, Tamil Nadu, India.
ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
Langmuir. 2023 Apr 4;39(13):4701-4711. doi: 10.1021/acs.langmuir.3c00010. Epub 2023 Mar 20.
The ability to modulate the size, the nanostructure, and the macroscopic properties of water-in-oil microemulsions is useful for a variety of technological scenarios. To date, diverse structures of water-in-alkane microemulsions stabilized by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) have been extensively studied. Even though the decisive parameter which dictates the phase behavior of micremulsions is the nature of the continuous phase, relatively very few reports are available on the structure and interactions in the microemulsions of aromatic oil. Here, we present a fundamental investigation on water-in-xylene microemulsions using small-angle neutron scattering (SANS) at a fixed molar ratio (ω) of water to AOT. We elucidate the microstructural changes in the water-AOT-xylene ternary system at dilute volume fractions (Φ = 0.005, 0.01, 0.03), where the droplet-droplet interactions are absent, to moderately concentrated systems (Φ = 0.05, 0.10, 0.15, and 0.20), where colloidal interactions become important. We also characterize the reverse microemulsions (RMs) for thermally induced microstructural changes at six different temperatures from 20 to 50 °C. Depending on the magnitude of Φ, the scattering data is found to be well described by considering the RMs as a dispersion of droplets (with a Schulz polydispersity) which interact as sticky hard spheres. We show that while the droplet diameter remains almost constant with increase in the volume fraction, the attractive interactions become prominent, much like the trends observed for water-in-alkane microemulsions. With increase in temperature, the RMs showed a marginal decrease in the droplet size but no pronounced dependence on the interactions was observed with the overall structure remaining intact. The fundamental study on a model system presented in this work is key to understanding the phase behavior of multiple component microemulsions as well as their design for applications at higher temperatures, where the structure of most RMs breaks down.
调节油包水微乳液的尺寸、纳米结构和宏观性质的能力在各种技术场景中都很有用。迄今为止，由双（2-乙基己基）磺基琥珀酸钠（AOT）稳定的烷烃包水微乳液的多种结构已得到广泛研究。尽管决定微乳液相行为的决定性参数是连续相的性质，但关于芳烃油微乳液的结构和相互作用的报道相对较少。在这里，我们使用小角中子散射（SANS）对水与AOT的固定摩尔比（ω）下的二甲苯包水微乳液进行了基础研究。我们阐明了在稀体积分数（Φ = 0.005、0.01、0.03）下，水-AOT-二甲苯三元体系中的微观结构变化，此时不存在液滴-液滴相互作用，到中等浓度体系（Φ = 0.05、0.10、0.15和0.20），此时胶体相互作用变得重要。我们还表征了在20至50°C的六个不同温度下热诱导微观结构变化的反相微乳液（RM）。根据Φ的大小，发现通过将RM视为液滴（具有舒尔茨多分散性）的分散体来很好地描述散射数据，这些液滴作为粘性硬球相互作用。我们表明，虽然液滴直径随体积分数增加几乎保持不变，但吸引相互作用变得突出，这与烷烃包水微乳液中观察到的趋势非常相似。随着温度升高，RM的液滴尺寸略有减小，但未观察到对相互作用的明显依赖性，整体结构保持完整。这项工作中提出的对模型系统的基础研究是理解多组分微乳液相行为以及它们在更高温度下应用设计的关键，在更高温度下大多数RM的结构会分解。
