On permanent cilia and segregation in the crystallization of binary blendsof monodisperse n-alkanes

The isothermal crystallization kinetics and morphology have been investigat ed for a series of dilute binary blends using six monodisperse n-alkanes as guest in C162H326 as host. Two patterns of behaviour were observed. Guest molecules shorter than the host segregate as a separate population causing growth rates to become both reduced and non-linear. Morphologies are then n oticeably less spherulitic than the host with less divergence between adjac ent dominant lamellae but exhibiting no additional splaying at zero superco oling. By contrast, those blends with an n-alkane longer than the host co-c rystallize (producing permanent cilia of controlled length) with a constant , but reduced, isothermal lamellar growth rate. Textures are now more spher ulitic than the host, with additional splaying of an amount directly propor tional to the number of permanent cilia and increasing with their length. T he intercepts and slopes of plots of splaying data against supercooling are consistently related to permanent cilia plus inclined packing of initially rough lamellar surfaces and transient ciliation, respectively. The underly ing causes of spherulitic growth for long molecules are thereby further con firmed and clarified. (C) 2001 Elsevier Science Ltd. All rights reserved.