Formation of Flat-on Lamellar Crystals in Absence of Nanoconfinement

Abstract

Flat-on lamellar crystals are crucial for gas-barrier polymer films. The formation of this lamellar crystalline structure with chains perpendicular to the substrate is currently understood as the result of confined crystallization, e.g., in block copolymers and ultrathin polymer films. In this paper, it is demonstrated that these flat-on lamellar crystals of various thermoplastic polymers may form on stainless steel and silicon wafer surfaces without the presence of confined crystallization. Atomic force microscopy, high-resolution scanning electron microscopy, and polarized light hot-stage microscopy are used to characterize the formation of the lamellar crystals. Further results show that the surface physicochemical properties of the substrates strongly influence the formation of these lamellar crystals. A hypothesis, based on the heterogeneous crystallization theory, is proposed to explain the formation of such flat-on lamellar crystals. These results are crucial for a fundamental understanding of the formation of lamellar crystals and may provide a new approach to fabricate such structures.