Controlled Switching from the Growth of Mono-Lamellar Polymer Crystals to the Formation of Stacks of Uniquely Oriented Lamellae

We have used a rationally designed two-step crystallization approach to induce the formation of stacks of superposed and uniquely oriented flat-on polymer lamellae exclusively and controllably at the periphery of mono-lamellar polymer crystals. The probability of initiating such stacks of lamellar crystals via self-induced nucleation was controlled by the crystallization temperature, which, in turn, determined the width of crystalline branches through the Mullins-Sekerka instability. We employed this approach for the formation of a “fence” of stacks of lamellar crystals at the periphery of mono-lamellar stereocomplex single crystals of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA). The resulting morphology resembled a “pseudo hollow crystal” with an almost empty interior of a size controllable by crystallization time. We believe that such approach can be applied also for other crystallizable polymers.