CRYSTALLIZATION IN OIL-IN-WATER EMULSIONS CONTAINING LIQUID AND SOLIDDROPLETS

The kinetics of crystallization of supercooled oil droplets in emulsio ns containing a mixture of solid and liquid n-hexadecane droplets has been monitored at constant temperature from time-dependent measurement s of the velocity of ultrasound. In emulsions stabilized by non-ionic surfactant (Tween 20 or C12E8) or anionic surfactant (sodium dodecyl s ulphate, SDS), crystallization is induced in liquid droplets when soli d droplets are present; in the absence of solid droplets crystallizati on proceeds at a negligible rate. Increasing the aqueous phase surfact ant concentration leads to a substantial increase in the crystallizati on rate in Tween 20 emulsions. Ionic strength has no significant effec t on the rate in SDS emulsions. The mechanism of this crystallization probably involves crystals on solid droplets penetrating into supercoo led liquid droplets during collisions and thereby acting as nucleation sites for crystal growth. The process is enhanced by aggregated surfa ctant molecules bridging between the colliding droplets.