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Quasi‐isothermal crystallisation kinetics, non‐classical nucleation and surfactant‐dependent crystallisation of emulsions
Author(s) -
Povey Malcolm J. W.,
Awad Tarek S.,
Huo Ran,
Ding Yulong
Publication year - 2009
Publication title -
european journal of lipid science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.614
H-Index - 94
eISSN - 1438-9312
pISSN - 1438-7697
DOI - 10.1002/ejlt.200800193
Subject(s) - nucleation , crystallization , pulmonary surfactant , coalescence (physics) , supercooling , isothermal process , kinetics , volume fraction , chemical engineering , particle size , thermodynamics , chemistry , materials science , organic chemistry , physics , quantum mechanics , astrobiology , engineering
Ultrasound velocity measurements were used to measure accurately the volume fraction of crystallised material in ‘monodispersed’ (120–2440 nm) n‐alkane and cocoa butter emulsions during crystallisation. The emulsions were temperature cycled, the ‘quasi’ isothermal nucleation rate determined from ultrasound velocity, and the crystallisation kinetics estimated. Emulsions were prepared using a variety of ‘emulsifiers’ (polyglycerol esters, Tween 20, Caflon phc060 and sodium caseinate). In practice, these emulsifiers behaved as stabilisers, preventing particle coalescence during collisions. The type of surfactant has a relatively small effect on the magnitude of the undercooling, which varied only a little (14.5–16.5 °C) as the emulsifier was changed, at a given particle size. On the other hand, the type of surfactant did make a significant difference to the crystallisation rate, once nucleation had been initiated. The surfactant type also altered the details of the crystallisation process. Reducing the size increased the nucleation rates dramatically in the size range studied in these experiments. It is suggested that dramatically increased droplet diffusion and collision rates are responsible for the observations in the case of droplets in the 100‐nm region. In the case of polyglycerol esters, the data suggests that they formed a solution with the n‐hexadecane.