The impact of salts on the stability of oil-in-water emulsions to coalescence was studied to aid in minimizing the impact of emulsified oils on natural water systems. Oil-in-water emulsions were fabricated from mineral oil, deionized water, and sodium lauryl ether sulfate. As salt (NaCl) concentrations increased from 0 to 1.25 M, an increase in emulsion stability to coalescence was observed over an aging period of 56 days. ζ potential and interfacial tension measurements showed that salt decreased the electrostatic repulsion of the anionic surfactant and allowed the surfactant to pack more densely at the oil–water interface. Dynamic interfacial tension measurements showed that surfactant adsorption rates increased with salt. As a result of faster adsorption kinetics, oscillating droplet tensiometry showed a decrease in the dilatational modulus when salt was present. An extended DLVO theory was used to calculate the interaction energy between droplets. These calculations agreed well with our experimental results indicating the importance of hydration forces at high salt concentrations and small droplet separation distances. The presence of salt allowed for close surfactant packing and faster surfactant adsorption kinetics, which prevented coalescence and created conditions favorable for the formation of a stable Newton black film.

中文翻译：

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盐水环境对阴离子表面活性剂稳定的水包油乳液聚结的影响

研究了盐对水包油乳液凝聚稳定性的影响，以帮助最大限度地减少乳化油对天然水系统的影响。水包油乳液由矿物油、去离子水和十二烷基醚硫酸钠制成。随着盐 (NaCl) 浓度从 0 增加到 1.25 M，在 56 天的老化期间观察到乳液对聚结的稳定性增加。ζ 电位和界面张力测量表明，盐降低了阴离子表面活性剂的静电排斥力，并使表面活性剂在油水界面上堆积得更密。动态界面张力测量表明，表面活性剂吸附率随着盐的增加而增加。由于更快的吸附动力学，当盐存在时，振荡液滴张力测定法显示膨胀模量降低。扩展的 DLVO 理论用于计算液滴之间的相互作用能。这些计算与我们的实验结果非常吻合，表明在高盐浓度和小液滴分离距离下水合力的重要性。盐的存在允许紧密的表面活性剂堆积和更快的表面活性剂吸附动力学，这防止了聚结并为形成稳定的牛顿黑膜创造了有利条件。