Modeling of Crystallization in a Blend Containing at Least One Crystallizable Component: An Analogy from Eutectic Systems

摘要

It is shown that crystalline/crystalline and crystallineoncrystalline blends can crystallize from the melt such that both components reside in the same spherulite. The observed morphology of such systems is that of growth arms of one component separated by regions rich in the other component. For crystalline/crystalline blends, cooperative crystallization is observed, such that the growth velocities of both species approach each other, allowing both components to crystallize nearly simultaneously. The crystallization and morphology of such systems are similar to those for eutectic crystallization of mixtures of small molecules. Existing analytical models describing the crystallization of eutectoid and eutectic systems of small molecules allow the growth velocity and the spacing of the alternating phases to be predicted. The model solves the moving boundary diffusion equation for the edgewise growth into the melt of a system of alternating plates of the two solid phases. Such a model has been adapted to the case of polymer blends. The problem is set up, and an analytical solution is found for low values of the Peclet number for crystallization V lambda/D_m. It is found that the velocity of growth V is sharply peaked when plotted against the interarm spacing lambda. Using measurements for a blend of high and low molecular weight poly(ethylene oxide)s, it is found that the operating condition for such growth corresponds to the maximum growth velocity. In the range of low Peclet numbers (low supercooling) reasonable agreement is found between measured and predicted values of both the growth velocity and the interarm spacing lambda.