Irreversible Adsorption Controls Crystallization in Vapor-Deposited Polymer Thin Films

Abstract

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.

Blocked crystallization in capped ultrathin polymer films studied by molecular simulations

“…Subsequently, the relaxed melts were quenched to a low temperature to observe isothermal crystallization. It was demonstrated that the crystallization temperature can also influence crystallization of the confined polymers . However, in the current work we mainly focused on the effects of interfacial interaction and film thickness on the crystallization of the confined polymers; the influence of temperature will be investigated in the future.…”

“…Jeong et al . found that crystallization of a totally adsorbed film of poly(ethylene oxide) is prohibited under the effect of strong polymer–substrate interactions . Recently, Napolitano et al .…”

Exploiting physical vapor deposition for morphological control in semi‐crystalline polymer films

“…Film formation proceeds by the addition of polymer molecules, as the volatile solvent gets pumped away . The polymer‐friendly technique has been applied to crystalline polymers such as PEO and PE for systematic crystallization studies . Furthermore, it allows for fabricating electronic and photonic devices with polymers .…”

“…Our investigation on crystallization of polymers thin films by MAPLE has been focused on the governing rules of crystallization kinetics occurring during extremely slow film growth . While MAPLE achieves concurrent film growth and crystallization similar to other PVD technologies, it is distinguished in that (1) the polymer is ejected from the target in the form of a polymer‐matrix clusters rather than a gas phase, and (2) the chemical nature and molecular weight of the target polymer can be preserved.…”

“…While MAPLE of PE does not show a noticeable evidence of adsorption due to the strong nature of PE to crystallize, the effect of droplet size and T dep on adsorption can be clearly observed in MAPLE‐deposited PEO. PEO films grown atop Si by MAPLE exhibit an adsorbed layer formed by the deposition of small PEO droplets that failed to nucleate . MAPLE of PEO at a temperature slightly below the bulk melting temperature (~60°C) can form a film that remains in liquid phase across the deposited area …”