Crystallization Behavior of Fats and Oils with Dr. David Pink скачать в хорошем качестве

Crystallization Behavior of Fats and Oils with Dr. David Pink

David Pink, PhD., Senior Research Professor, at St. Francis Xavier University in Canada, presents 'Crystal memory near discontinuous triacylglycerol phase transitions: models, metastable regimes and critical points' and 'Computing the Fractal Dimensions of Aggregates' at the Virtual 2020 AOCS Annual Meeting & Expo. https://www.eventscribe.com/2020/AOCS/ #AOCS2020 Abstracts Crystal memory near discontinuous triacylglycerol phase transitions: models, metastable regimes and critical points It is proposed that “crystal memory”, observed in the solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystals and liquid TAG molecules, in a superheated metastable regime. In the superheated regime of a system exhibiting a single phase transition, solid crystals can act as heterogeneous nuclei onto which molecules can condense as the temperature is lowered after the system has been heated. This process is interpreted as a “crystal memory” effect. We outline a mathematical model, with a single phase transition, that shows how the observations can be explained, makes predictions and relates them to recent experimental data. A modified Vogel-Fulcher-Tammann (VFT) equation is used to predict time-temperature relations for the observation of “crystal memory” and to show boundaries beyond which “crystal memory” is not observed. The “holding time” is associated with the lifetime of a metastable state and a plot of lifetime versus temperature, using the modified VFT equation, is in agreement with recent data. The model possesses a critical point and we outline a procedure describing how it could be observed by changing the hydrocarbon chain length. We make predictions about how thermodynamic functions will change as the critical point is reached and as the system enters a crossover regime. Computing the Fractal Dimensions of Aggregates A knowledge of the mass fractal dimension of aggregated solids in edible oils, for example, can provide us with an understanding of the factors which affect diffusion in such systems and the system’s response to shear, such as identifying the boundaries of shear banding. Mass fractal values can also guide the manufacture of new products when looking to replace one of the ingredients. Some of the techniques which have been used to characterize fractal structures in edible fats and oils are (1) light microscopy and the box counting method, (2) neutron scattering and (3) X-ray scattering. The box counting method relies on the scaling of two-dimensional images of the solid structures as functions of the size of areas that become progressively smaller, while scattering methods rely on an interpretation of the scattering intensity, I(q), or the structure function, S(q), as a function of the scattering vector q. This talk will present a brief overview of the mathematics of these techniques and show how erroneous conclusions can arise from their use. Questions regarding, for example, (a) the discarding of information by dimensional reduction of the experimental data, (b) the ignoring of aspects of polydispersity in the experimental samples, and (c) the use of insufficient I(q) data, will be addressed. The perils associated with these approaches will be illustrated by computer simulation and animated graphics. https://www.eventscribe.com/2020/AOCS/ #AOCS2020