Phase Transformations in Emulsions. I Phase Transformations in Emulsions : Part I : Effects of Thermal Treatments on Nucleation Phenomena : Experiments and Model

Experiments have been performed by D.S.C, on emulsified materials such as water, aqueous saline solutions, metals and organic compounds. During the cooling-heating cycle following the preparation of the emulsion,the droplets crystallize around the temperature T*< TFand melt at TFDuring the next cooling the organic substances as well as tin, crystallize around T*andalsoata higher temperature T* *, The number of droplets crystallizing at T* Is strongly dependent upon the number and the limits of the freeze-thawing cycles performed previously. Wa ter or benzene emulsions crystallize also around two temperatures T* and T* * when a first crystallization has been obtained at a fixed temperature θc(T'<θc θ'>T'). In particular the onset time during which no crystallizations are observed Is shortened. Different possible mechanisms are presented and analyzed. In the model retained, nucleation Is supposed to occur at the surface of the emulsified droplet witha non uniform probability. Preferential nucleating patches are created by the previous crystallizations of the droplets during a steady cooling or at a fixed temperature θc.