Formation of Stacked Three-Dimensional Polymer Single Crystals

Stacks of crystalline lamellae all having a uniquely oriented hexagonal shape, referred to as 3D (three-dimensional) single crystals, were obtained via isothermal crystallization of isotactic polystyrene at a temperature close to the melting point. The height of the stacks of lamellae reached several micrometers corresponding to hundreds of superposed lamellar crystals. We propose that the mechanism of self-induced nucleation allowed propagating the orientation of the basal lamellar crystal to all other lamellae in the stack. The unique orientation of all lamellae was reflected by the preference of cracks to form along the diagonals of the hexagonal stack. Cracks were caused by a mismatch in the coefficients of thermal expansion of the substrate and 3D single crystals during quenching from the crystallization temperature to room temperature. We believe that the presented growth mechanisms leading to 3D single crystals can be observed for all crystallizable polymers including block copolymers with a noncrystallizable block.

Automated summary

3D single crystals with uniquely oriented hexagonal shape were obtained by isothermal crystallization of isotactic polystyrene. The cracks tended to form along the diagonals of hexagonal stack due to mismatch in coefficients of thermal expansion during quenching. The growth mechanisms leading to 3D single crystals can be observed for all crystallizable polymers.