Evaporation Induced Crystallization of Poly (L-lactide acid) on Water Surface*

Polymer self-assembly and crystallization on water surfaces have been extensively investigated to understand polymer chain conformation on water surfaces and to fabricate free-standing polymer thin films. The Langmuir–Blodgett (LB) approach is often used in this research field as it provides a well-controlled water/air interface. In this study, we introduce an evaporation crystallization process to investigate polymer crystallization on water surfaces. Poly (L-lactic acid) (PLLA) was used as the model polymer and PLLA crystals were obtained by controlling solvent evaporation on the water surface. The crystal structure and morphology were investigated using transmission electron microscopy and atomic force microscopy. We show that water surface plays a critical role in determining PLLA chain conformation, which in turn, leads to different crystal morphologies including one-dimensional ribbons and two-dimensional plates. The evaporative crystallization technique, therefore, provides a unique opportunity to tune polymer crystallization pathways.