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The extensive experimental data reported by Smith et al. (Eur. J. Lipid Sci.Technol.2005, 107, 583−593) on the metastable zone width of 1,3-dipalmitoyl-2-oleoylglycerol, (POP) tripalmitoylglycerol (PPP), and their mixtures in acetone are analyzed using a novel approach based on classical three-dimensional nucleation theory (Sangwal, K. Cryst. Growth Des.2009, 9, 942−950) and a self-consistent Nývlt-like approach (Sangwal, K. Cryst. Res. Technol.2009, 44, 231−247) to obtain quantitative information on the processes of nucleation of these systems. The relevant equations of the above approaches are (i) (T0/ΔTmax)2 = F(1 − Z ln R) and (ii) ln(ΔTmax)/T0) = Φ + β ln R, where T0 is the saturation temperature and F and Φ are, respectively, the values of (T0/ΔTmax)2 and ln(ΔTmax)/T0) when ln R = 0, whereas Z is a parameter characteristic of the crystallizing system and the constant β is inverse of the apparent nucleation order m in the Nývlt approach. It was found that (1) the value of parameters β and Z is relatively insensitive to saturation temperature T0 but depends on the investigated compound and the technique used for the measurement of maximum supercooling ΔTmax and the presence of PPP impurity in POP solutions; (2) the values of β and Z for PPP and POP decrease with an increase in their solubility in acetone; and (3) the data of Φ and ln(F1/2) as a function of saturation temperature T0 follow the Arrhenius-type relation with an activation energy Esat. Analysis of the results revealed that (1) the values of β and Z are directly connected with the solid−liquid interfacial energy γ; (2) the value of Esat depends on the nature of ions/molecules participating in diffusion; (3) maximum supercooling ΔTmax measured by turbidimetry corresponds to a nucleation event alone, but that obtained from growth exotherm includes some contribution of growth of stable nuclei after nucleation; and (4) PPP impurity in POP solutions promotes crystallization by acting as growth centers for heterogeneous nucleation.
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