Kinetics of crystallization in n-hexadecane and cocoa butter oil-in-water emulsions accounting for droplet collision-mediated nucleation

Droplet collision is shown to be important in the propagation of nucleation through supercooled oil-in-water emulsions by the use of a novel membrane technique, On the other hand, nucleation mediated by Tween 20 micelles is s hown to be of relatively much less importance in both n-hexadecane and coco a butter oil-in-water emulsions. The droplet collision phenomenon probably occurs via a surfactant bridge between the colliding droplets;When this pro cess is taken into account we show that the Turnbull model for crystal nucl eation kinetics explains very well nucleation in cocoa butter oil-in-water emulsions by seed crystals, On the basis of this model we characterized the seed crystals in cocoa butter via isothermal crystallization studies at 14 .2, 15.0, 15.5, and 15.8 degreesC, We suggest that there are few seed cryst als whose size exceeds 0.28 mum at 80 degreesC, In our cocoa butter samples there were between 10(16) and 10(17) seed crystals m(-3) whose average siz e we inferred to be less than 0.09 mum. A value of 0.133 mJ m(-2) is obtain ed for the Gibbs free energy of the nucleating surface in our West African cocoa butter samples. There is evidence that the cy-polymorph of POS compri ses the nucleating layer in the seed crystal. There is no evidence that sur factant influences the primary nucleation of oil crystals. However, the sur factant has a big effect on the kinetics of the secondary nucleation proces s, mediated by droplet collision, (C) 2000 Academic Press.