Crystallization in Poly(Ethylene Oxide) Thin Films: Roles of Shear, Confinement, and Homoepitaxy.

Lammelar orientation during crystallization in poly(ethylene oxide) (PEO) thin films is governed by three competing mechanisms, which we elucidate using pseudo-polyrotaxane nanosheets (PPRNSs) and their end-capped analogues (cPPRNSs) as model fillers. Shear forces during processing favor edge-on lamellae, while confinement at high filler loadings promotes flat-on orientation. PPRNSs introduce a third mechanism-homoepitaxial templating-that directs flat-on crystallization through specific matrix-filler interactions absent in cPPRNSs. Systematic orientation analysis before and after thermal recrystallization reveals distinct switching behaviors. cPPRNS composites exhibit edge-on lamellae initially, which transition to mixed or flat-on orientations upon recrystallization depending on filler concentration. In contrast, PPRNSs impose flat-on orientation directly during processing at sufficiently high filler loading and maintain robust flat-on orientation after thermal recrystallization across the investigated concentration range. These findings establish predictive guidelines for tuning lamellar orientation in ultrathin polymer films, with implications for flexible electronics, optical devices, and barrier materials.