Koroleva M, Nagovitsina T, Yurtov E
Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125047, Russia.
Phys Chem Chem Phys. 2018 Apr 18;20(15):10369-10377. doi: 10.1039/c7cp07626f.
The prevailing opinion in the literature is that the main mechanism of O/W nanoemulsion degradation is Ostwald ripening. Nevertheless, the experimental rates of Ostwald ripening are usually several orders of magnitude higher than the theoretical values. This suggests that other mechanisms, such as coalescence, flocculation and subsequent creaming, significantly influence nanoemulsion breakdown. We investigated O/W nanoemulsions stabilized by Brij 30 or by a mixture of Tween 80 and Span 80 and with liquid paraffin as a dispersed phase. The results indicate that Ostwald ripening is the main process leading to nanoemulsion coarsening only in nanoemulsions with low oil phase fractions of up to 0.05. For quasi-steady state conditions the rates of Ostwald ripening are equal to (1.5 ± 0.3) × 10-29 and (1.1 ± 0.3) × 10-29 m3 s-1 in nanoemulsions with Brij 30 and Tween 80 & Span 80, respectively. In nanoemulsions with oil phase fractions of 0.15-0.45, different mechanisms are identified. Flocculation prevails over other processes during the first days in nanoemulsions stabilized by Brij 30. Coalescence is the main mechanism of nanoemulsion degradation for long times. An increase in droplet size 5-10 days after nanoemulsion preparation due to Ostwald ripening takes place in the case of nanoemulsion stabilization by Tween 80 and Span 80. The stability behavior of these nanoemulsions at later stages is distinctly affected by coalescence and flocculation.
文献中的主流观点是，O/W纳米乳液降解的主要机制是奥氏熟化。然而，奥氏熟化的实验速率通常比理论值高几个数量级。这表明其他机制，如聚结、絮凝以及随后的乳析，对纳米乳液的分解有显著影响。我们研究了由Brij 30或吐温80与司盘80的混合物稳定、以液体石蜡为分散相的O/W纳米乳液。结果表明，仅在油相分数低至0.05的纳米乳液中，奥氏熟化才是导致纳米乳液粗化的主要过程。对于准稳态条件，在由Brij 30和吐温80与司盘80稳定的纳米乳液中，奥氏熟化速率分别等于(1.5±0.3)×10⁻²⁹和(1.1±0.3)×10⁻²⁹立方米每秒。在油相分数为0.15 - 0.45的纳米乳液中，确定了不同的机制。在由Brij 30稳定的纳米乳液中，絮凝在最初几天比其他过程更为显著。聚结是纳米乳液长时间降解的主要机制。在由吐温80和司盘80稳定的纳米乳液中，由于奥氏熟化，纳米乳液制备后5 - 10天液滴尺寸会增加。这些纳米乳液后期的稳定性行为明显受到聚结和絮凝的影响。
