Irreversible Adsorption Controls Crystallization in Vapor-Deposited Polymer Thin Films.

Matrix-assisted pulsed laser evaporation (MAPLE) provides a gentle means for the quasi-vapor deposition of macromolecules. It offers a unique opportunity for the bottom-up control of polymer crystallization as film growth and crystallization occur simultaneously. Surprisingly, with increasing deposition time, it has been shown that crystallization becomes prohibited despite the availability of polymer via continuous deposition. In this Letter, we investigate the molecular origins of suppressed crystallization in poly(ethylene oxide) films deposited by MAPLE atop silicon substrates. We find that suppressed crystallization results from the formation of an irreversibly adsorbed polymer nanolayer at the substrate that forms during deposition. Substrate temperature is shown to influence the stability of the irreversibly adsorbed nanolayer and, hence, polymer thin film crystallization. Our investigation offers new insight into how temperature and interfacial interactions can serve as a new toolbox to tune polymer film morphology in bottom-up deposition.