Experimental evidence for crystallization of polymer thin films with different interfacial environments

Abstract

Studies on polymer crystallization under confinement typically rely on crystalline polymer thin films supported on solid substrates, where geometric confinement and solid substrate effect are inherently coupled. Here, a sacrificial layer strategy is employed to fabricate freestanding poly(L-lactic acid) (PLLA) thin films, enabling systematic investigation of crystallization under distinct interfacial environments, including air/solid, liquid/solid, air/air, and liquid/liquid combinations. This approach allows direct observation of crystallized morphologies from the bottom side of the films and provides a method to study crystallization in the absence of substrate. Comparison of crystalline roughness on both sides of the films reveals that solid silicon substrates restrict PLLA chain mobility and suppress crystallization, whereas liquid interfaces enhance chain mobility and facilitate crystallization. These results provide direct experimental evidence for substrate effects on the crystallization of polymer thin films.