Abstract
A model for heterogeneous nucleation of isotactic polypropylene in terms of a “cylindrical cap” with the critical size and barrier set by a contact angle is described. Quiescent crystallization data for bulk samples of isotactic polypropylene are analyzed to extract a contact angle in the range of 40° to 70° with a mean value of 56°, which corresponds to a factor of 6 decrease in the critical barrier from the homogeneous case. This value is in reasonable agreement with the contact angle of 79° ± 3° estimated from molecular scale theory (DOI 10.1021/ma400703m). This model could be combined with calculations from melt rheology of entropy reduction due to flow to frame discussions of flow-induced crystallization.
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