Impurity effects on crystallization rates of n-hexadecane in oil-in-water emulsions

Crystallization rates of n-hexadecane dispersed in oil-in-water (O/W) emuls ion toil 20 wt% and water 80 wt%) were studied by an ultrasonic velocity me asurement technique. Tween 20 was employed for emulsification to form the O /W emulsion. A highly hydrophobic food emulsifier, a sucrose polyester invo lving palmitic acid moiety (P-170), was added to n-hexadecane, as an impuri ty, in an attempt to modify the rate of the crystallization of n-hexadecane . The rates of crystallization of n-hexadecane were monitored by variations in the ultrasonic velocity values, which increase with increasing amount o f crystal fractions in the oil phase of the emulsion. In comparison with th e results of the O/W emulsion systems with those of the bulk systems, the f ollowing results were obtained; (a) the addition of P-170 accelerated the n ucleation in the emulsion system, yet no acceleration was revealed in the b ulk system, (b) the rates of crystal growth were retarded by the addition o f P-170, (c) the acceleration of nucleation occurred through two stages wit h increasing concentrations of P-170: e.g., a sharp increase occurred in a low concentration range of P-170 up to 0.3% with respect to n-hexadecane, t hen a moderate acceleration occurred at P-170 concentrations above 0.6%. Th ese results were discussed in terms of heterogeneous nucleation occurring a t interfaces of the O/W emulsion droplets. (C) 1999 Elsevier Science B.V. A ll rights reserved.