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Potential mechanisms affecting growth rate dispersion (GRD) are investigated. Previous studies have identified surface roughness and internal lattice perfection as key mechanisms which are both evaluated with respect to GRD. Crystal growth of potassium dihydrogen phosphate was studied in two solvent mixtures, water and water-ethanol. The surface roughness was analyzed by atomic force microscopy and the internal crystal perfection by X-ray diffraction using a synchrotron source. The crystals grown at higher supersaturation have more pronounced and more frequent surface irregularities, supporting previous findings on a feedback mechanism between surface roughness and growth rate. No significant relationship was found between internal crystal perfection and growth rate, however, this is likely due to the size of the crystals analyzed herein and not the absence of any such mechanism in small crystals. [ABSTRACT FROM AUTHOR]

The effects of tacticity and molecular weight (MW) of isotactic polypropylene (iPP) on crystallization kinetic and crystal morphology were investigated by in-situ isothermal crystallization using simultaneous synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) techniques. Several quantitative parameters were extracted and analyzed in details. It was found that tacticity notably influenced the rate of nuclei seeding, where the high-tacticity iPP sample exhibited a faster nucleation rate. However, tacticity affected only slightly on the crystallization and normalized spherulite-growth rates. Inversely, the MW strongly influenced the crystal lamellar morphology, in which the amorphous layer thickness (L a) was found to be larger in high-MW iPP than that in low-MW iPP. These findings indicated the behavior of "tapering" in the lamellar width during crystal growth, where tacticity and MW both played a role in this process. Image 1 • Tapering in lamellar width of polypropylene is evidenced, for the first time. • Both molecular weight (MW) and tacticity play the role on the tapering process. • Tacticity strongly influences the crystallization kinetic, while MW notably affects the lamellar morphology. [ABSTRACT FROM AUTHOR]

Crystal growth rate dispersion (GRD) and size-dependent crystal growth (SDG) models are models to extend McCabe's L Law to more accurately account for variation in the crystal growth rates within a population of crystals. GRD is a phenomenon where the crystal growth rate either fluctuates randomly over time or varies over a population of crystals. SDG is where the growth rate of a crystal depends on its size, typically with growth rates assumed to increase monotonically with crystal size. Although it has been recognized for more than 30 years that, except for extremely small crystals, SDG is an artifact of GRD, it is still common in the literature for GRD in experimental results to be modeled using SDG models. This discussion will present some background and new experiments on the mechanism and extent of GRD to demonstrate that GRD is a real phenomenon, whereas SDG is largely an artifact, and some modeling work to demonstrate that SDG models cannot successfully replicate crystal size distribution data that originate due to GRD. More work needs to be done in accurate population balance modeling for processes where GRD is significant rather than assuming that SDG models are adequate. [ABSTRACT FROM AUTHOR]