Further studies on the effect of degassing on the dispersion and stability of surfactant-free emulsions
Further studies on the effect of degassing on the dispersion and stability of surfactant-free emulsions
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DOI：
10.1021/la036028g
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发表时间：
2004-04-13
期刊：
影响因子：
3.9
通讯作者：
Pashley, RM
中科院分区：
文献类型：
--
作者：
Maeda, N;Rosenberg, KJ;Pashley, RM
最近报道的结果表明，无表面活性剂的水包油乳液的形成可以通过几乎完全去除溶解的气体而显著增强，并且溶解的气体的重新引入不会立即使已经形成的乳液不稳定。这些最初的实验已经被重复和扩展，以包括更广泛的有机液体和光散射的应用，以确定液滴的大小和分布。先前的观察得到了证实。此外，发现油在水中的溶解度与脱气油滴在水中的稳定性（寿命）之间存在系统趋势。溶解度越低，乳液越稳定，并且对于微溶于水的油如角鲨烷，小液滴保持稳定数周，浮力分离是大液滴随时间不稳定的主要原因。电解质的添加，高达摩尔浓度，大大降低了增强的分散体脱气，但似乎对已经形成的乳液的稳定性几乎没有影响。将pH降低至约2显著降低了分散体对脱气的增强和已经形成的乳液的稳定性。相反，pH增加到约11几乎不影响分散体对脱气的增强或已经形成的乳液的稳定性。我们已经证实了溶解气体的重要性及其与静电效应的关联，但我们仍然不能提供一个完整的解释脱气对疏水分散体的影响。
Recently reported results indicate that the formation of surfactant-free, oil-in-water emulsions can be significantly enhanced by the almost complete removal of dissolved gases and that the reintroduction of dissolved gases does not immediately destabilize the already-formed emulsions. These initial experiments have been repeated and extended to include a wider range of organic liquids and the application of light scattering to determine droplet size and distribution. The earlier observations have been confirmed. In addition, a systematic trend was found between the solubility of the oil in water and the stability (lifetime) of the degassed oil droplets in water. The lower the solubility, the more stable the emulsion, and for oils that are sparingly soluble in water such as squalane, the small droplets remain stable for several weeks, with buoyancy separation being the main cause of instability of the large droplets with time. The addition of electrolytes, up to molar concentrations, substantially reduces the enhancement of the dispersions on degassing but appears to have little effect on the stability of the already-formed emulsions. The reduction of pH to about 2 significantly reduces both the enhancement of the dispersions on degassing and the stability of the already-formed emulsions. In contrast, the increase of pH to about 11 hardly affects the enhancement of the dispersions on degassing or the stability of the already-formed emulsions. We have confirmed the importance of dissolved gas and its association with the electrostatic effects, but we still cannot provide a complete explanation for the effect of degassing on the hydrophobic dispersions.