Water <-> ice transformation in micron-size droplets in emulsions

Year: 1999

Authors: Tombari E., Ferrari C., Salvetti G., Johari G.P.

Autors Affiliation: CNR, Ist Fis Atom & Mol, I-56127 Pisa, Italy; McMaster Univ, Dept Mat Sci & Engn, Hamilton, ON L8S 4L7, Canada

Abstract: To investigate the crystallization and melting behaviors of micron-size droplets in a water-emulsion, the heat capacity, C-p, has been studied by adiabatic calorimetry over the 233-273 K range. Water droplets in the emulsions began to crystallize at ca. 243 K, but the crystallization rate was slow. This was caused partly by the relatively slow coalescence of crystallized and uncrystallized droplets at that temperature, in a highly nonNewtonian viscous media of the emulsion. Crystallization occurred rapidly on heating and remained incomplete even when it occurred at 260 K. Thus a substantial amount of water droplets coexisted with ice droplets in the emulsion. The onset of crystallization shifted to lower T and the number of water droplets in the emulsion at a given T decreased as the droplets grew on thermally cycling the emulsion. C-p of emulsion increased progressively more rapidly as 273 K was approached, which is attributable to premelting of the ice droplets beginning at 260 K. Analysis of the C-p data showed that interaction between the droplets and the surfactant in the emulsion changes on crystallization. This is attributable to the decrease in the entropy at the surfactant-water interface. (C) 1999 American Institute of Physics


Volume: 111 (7)      Pages from: 3115  to: 3120

DOI: 10.1063/1.479592

Citations: 15
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