Diffusion-Limited Lamellar Thickening in Poly(ethylene oxide) Ultrathin Films

The growth behavior and lamellar thickness ( d c ) of poly(ethylene oxide) (PEO) crystals were investigated by optical microscopy (OM) and atomic force microscopy (AFM) in ultrathin films (thickness h ∼ 10–30 nm). We found that as crystallization temperature ( T c ) rises from 55 to 60 °C, d c increases by approximately 11 nm (nearly double) for the 11.5 nm ultrathin film, in contrast to only 5.5 nm (approximately 23%) for the 26 nm thin film. This may be attributed to the stronger spatial confinement and interfacial effects in thinner films that significantly hinder chain diffusion, thus limiting lamellar thickening, especially at lower T c . Additionally, when h is below the critical thickness h * ∼ 5 R g, both the early stage growth rate ( G e ) and d c decrease as h decreases at a constant T c of 56 °C. This indicates that, within the studied range of h, the suppression of lamellar thickening by diffusion limitation outweighs the promoting effect of the reduced growth rate. Further, the increments in early stage growth rate (Δln G e ) and lamellar thickness (Δ d c ) follow a power law: Δ d c ∼ Δln G e n, where the power-law exponent n increases with decreasing T c, indicating a stronger limitation of chain diffusion on lamellar thickening at lower temperatures in ultrathin films. These findings demonstrate diffusion-limited lamellar thickening in ultrathin film and highlight the key role of chain mobility, advancing the understanding of confined polymer crystallization.