表面活性剂结晶对水包十二烷纳米乳液聚集速率的影响。外相粘度的变化
Influence of surfactant crystallization on the aggregation rate of dodecane-in-water nanoemulsions. Changes in the viscosity of the external phase
摘要：
在超过500 mM NaCl时，评价用7.5 mM十二烷基硫酸钠（SDS）稳定的水包十二烷（d/w）纳米乳液的聚集速率。在十六烷在水（h/w）乳液的情况下，它被发现，絮凝率明显降低与离子强度，偏离明显从理论预测。由于多粒子模拟被证明是非常耗时的，实验参数的准确知识是必要的实现之前，进一步的评估。在此，由于表面活性剂相行为引起的水溶液粘度的变化被认为是所述现象的可能原因。外部粘度对模拟结果的影响进行评估，使用在给定的盐浓度下的表面活性剂溶液的实际粘度与其在不存在盐的情况下的值之间的商。为此，在20和25 °C的温度下，在300和900 mM NaCl之间测量0.5和7.5 mM SDS溶液的粘度。结果表明，由于表面活性剂晶体的形成而引起的水溶液粘度的增大，显著降低了聚集速率。然而，这种下降似乎不足以证明在25 ℃时观察到的肯德基下降是合理的。然而，值得注意的是，表面活性剂溶液温度的5度变化引起kFC的显著降低。此外，一组两粒子模拟在这里使用的粘度贡献的评估，以说明这种方法的局限性。证实了这种方法仅便于研究相互作用势对聚集速率的影响，因为它以前是由Fuchs [1936]设想的。
英文摘要：
Rates of aggregation of dodecane-in-water (d/w) nanoemulsions stabilized with 7.5 mM sodium dodecylsulfate (SDS) are evaluated beyond 500 mM NaCl. As in the case of hexadecane-in-water (h/w) emulsions, it is found that flocculation rates apparently decrease with the ionic strength, departing appreciably from theoretical predictions. Since many-particle simulations proved to be very time consuming, an accurate knowledge of experimental parameters is necessary prior to the realization of further evaluations. Here, the change in the viscosity of the aqueous solution due to the surfactant phase behavior is considered as a possible cause of referred phenomenon. The influence of the external viscosity on the outcome of the simulations is appraised using a quotient between the actual viscosity of the surfactant solution at a given salt concentration and its value in the absence of salt. For that purpose, the viscosity of 0.5 and 7.5 mM SDS solutions was measured between 300 an 900 mM NaCl for temperatures of 20 and 25 °C. It is concluded that the augment of the aqueous viscosity due to the formation of surfactant crystals diminish significantly the aggregation rate. Yet this decline seems insufficient to justify the observed reduction of kFC at 25 C. Nevertheless, it is noteworthy that a 5-degree change in the temperature of the surfactant solution causes a remarkable decrease of kFC . Additionally, a set of two-particle simulations is used here to illustrate the limitations of this methodology for the appraisal of the viscosity contribution. It is confirmed that such approach is only convenient to study the effect of the interaction potential on the aggregation rate, as it was formerly conceived by Fuchs [1936].
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