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The coarsening of droplets in an emulsion with a size distribution that initially is given by the Lifshitz−Slyozov−Wagner (LSW) distribution is studied by means of numerical calculations taking into account elastic interfacial behavior. Droplets smaller than the critical radius will shrink while droplets larger than the critical radius will grow. For a zero interfacial elasticity the stationary LSW distribution is obtained and its coarsening rate matches theoretical values. The critical droplet radius, number-averaged droplet radius, and volume-surface-averaged droplet radius increase with time. Low interfacial elasticity with respect to initial interfacial tension causes the initial LSW distribution to become bimodal. The size distribution of the coarsening peak can still be described by the LSW distribution. The smaller peak that accumulates in time has an average radius that depends on the ratio between the interfacial elastic modulus and the interfacial tension. For large ratios (E/σ > 1), the system goes within a short time to a stable situation without changes in particle size with time.

The crystallization kinetics of mixtures of fully hydrogenated palm oil (HP) in sunflower oil (SF) was studied. The thermal properties and phase behavior of this model system were characterized by means of differential scanning calorimetry and X-ray diffraction. From the melting enthalpy and clear point of HP, it was possible to calculate the supersaturation at a given temperature for every composition of the model system. Supersaturation of the model system for the β′ but not for the α polymorph yielded the β′ polymorph, while supersaturation for the α polymorph yielded a mixture of mainly β and some β′ polymorphs. The crystallization kinetics of HP/SF mixtures were determined by pulsed wide-line proton nuclear magnetic resonance for various initial supersaturations in the β′ polymorph. The determined curves were modeled by a modified classical nucleation model and an empirical crystal growth function, which are both functions of supersaturation. Heterogeneous nucleation rates in the β′ polymorph yielded a surface Gibbs energy for heterogeneous nucleus formation of 3.8 mJ·m −2 . About 80% of the triglyceride was assumed to be in a suitable conformation for incorporation in a nucleus. Induction times for isothermal crystallization in the β′ polymorph yielded a surface free energy for heterogeneous nucleus formation of 3.4 to 3.9 mJ·m −2 .

The purpose of this study is to determine characteristic nucleation parameters such as the surface free energy for nucleus formation in mixtures of fully hydrogenated palm oil (HP) in sunflower oil (SF). These parameters will be used to model the bulk crystallization kinetics of the same mixtures. This was achieved by determining the crystallization kinetics in emulsified triglyceride mixtures using differential scanning calorimetry, proton nuclear magnetic resonance, and ultrasound velocity measurements. The latter technique appeared to be very sensitive for monitoring the crystallization kinetics of fat dispersions containing triglycerides with a simple phase behavior. Isothermal crystallization of emulsified HP stabilized by sodium caseinate started at 7 K below the α clear point, and the kinetics were best fitted assuming heterogeneous nucleation. Isothermal crystallization of emulsified 10% HP in SF stabilized by caseinate started at 14 K below the α melting point, and the kinetics were best fitted assuming homogeneous nucleation. If the same dispersion was stabilized by Tween 20, crystallization started at 11 K below the α melting point, and the kinetics were fitted best using heterogeneous nucleation. Analysis of the temperature dependency of the fit parameters yielded a surface free energy of a nucleus of about 4 mJ·m −2 in the case of homogeneous nucleation. Pre-exponential nucleation frequencies indicated that a large proportion of the triglyceride molecule should be in the right conformation to be incorporated in a nucleus.Nucleation is an essential step in crystallization, but it also is the step that is least accessible to experiments. Nucleation is the formation of ordered domains by random association of molecules up to a certain critical size. It determines how many crystals will be formed and therefore their final average size. A dispersion of fat crystals with a large number of small crystals may have desired properties such as a good spreadability but for crystal separation purposes it is undesired.With homogeneous nucleation, no surface acts as catalyst: the crystallizing molecules spontaneously form nuclei. Homogeneous nucleation conditions are normally reached only when the solution or melt is dispersed into a number of droplets that exceeds the number of catalytic impurities present in the system. For crystallization of dispersed tristearate and tripalmitate, supercooling of up to 26 K in the α polymorph was observed (1,2). For emulsified milk fat, supercooling up to 20 K below the α clear point was obtained (3).In bulk fats, supercooling of only a few K is needed to induce crystallization. This is explained by the presence of (solid) impurities of a size larger than the dimensions of a nucleus. These impurities can act as a catalyst for nucleation by lowering the activation Gibbs energy for formation of a nucleus. It is assumed that nucleation in bulk fats will often be heterogeneous (4).The concentration of catalytic impurities is important for modeling the crystallization kinetics of bul...