McClements DJ, Dungan SR
Department of Food Science and Technology, University of California, Davis, California, 95616
J Colloid Interface Sci. 1997 Feb 1;186(1):17-28. doi: 10.1006/jcis.1996.4504.
Pulsed nuclear magnetic resonance was used to monitor the crystallization of supercooled liquid droplets in 30 wt% n-hexadecane oil-in-water emulsions at 6°C. Crystallization was induced in the liquid droplets when solid droplets of the same material were present. The rate of induced crystallization increased as the concentration of free non-ionic surfactant (polyoxyethylene sorbitan monolaurate) in the aqueous phase increased from 0 to 14 wt%. Differential scanning calorimetry measurements indicated that free surfactant had no effect on crystal nucleation of individual droplets. These results indicate that the surfactant enhances induced crystallization by altering colloidal interactions between droplets. Creaming measurements showed that flocculation was enhanced in emulsions when the free surfactant concentration was increased. We propose that the presence of free surfactant micelles increases the attraction between droplets because of an osmotic effect, and this attraction facilitates the ability of solid crystals from one droplet to induce crystallization in an adjacent liquid droplet.
采用脉冲核磁共振技术监测了6℃下30 wt%正十六烷水包油乳液中过冷液滴的结晶过程。当存在相同材料的固体液滴时，液滴中会诱导结晶。随着水相中游离非离子表面活性剂（聚氧乙烯山梨醇酐单月桂酸酯）浓度从0 wt%增加到14 wt%，诱导结晶速率增加。差示扫描量热法测量表明，游离表面活性剂对单个液滴的晶体成核没有影响。这些结果表明，表面活性剂通过改变液滴之间的胶体相互作用来增强诱导结晶。乳析测量表明，当游离表面活性剂浓度增加时，乳液中的絮凝作用增强。我们认为，游离表面活性剂胶束的存在由于渗透效应增加了液滴之间的吸引力，这种吸引力促进了一个液滴中的固体晶体在相邻液滴中诱导结晶的能力。
