The effect of de-gassing on the dispersion of fine oil droplets in water

Several recent studies have demonstrated that a wide range of hydrophobic, water-insoluble oils can be readily dispersed in water following a simple freeze–thaw process of de-gassing. The oil droplets typically appear to be sub-micron sized and are fairly mono-disperse. They do not coalesce but slowly phase-separate or settle under gravity. This behaviour applies to a wide range of oils including, hydrocarbons, fluorocarbons and silicones. There is also some evidence that finely divided hydrophobic solid powders can also be more readily dispersed in de-gassed water. The enhanced dispersion is thought to be caused by the removal of gas nucleation solutes that is dissolved gas molecules, which would otherwise facilitate cavitation between two hydrophobic surfaces. The almost complete removal of dissolved gases appears to prevent this cavity formation and so hydrophobic particles are more easily dispersed in water. This new area has some interesting applications to several important industries. Some recent results are presented and a simple theoretical explanation is proposed to explain the fine distribution of droplet sizes observed.