Morphological Variation of the Poly(ε-caprolactone) Crystals in Bulk, Thin and Ultrathin Films of Poly(ε-caprolactone)/Poly(vinyl methyl ether) Blends

Bulk, thin and ultrathin films with different thicknesses of neat poly(epsilon-caprolactone) and its blends with poly(vinyl methyl ether) were prepared on silicon substrate by spin coating from dilute solution with various composition ratios. The as-prepared film was melted above the equilibrium melt temperature and subsequently crystallized over wide temperature ranges. For the neat poly(epsilon-caprolactone) and its blends, the as-prepared films show band morphology with concentric extinction rings. For ultrathin films, the morphology is changed to a different shape depending on the crystallization conditions. The neat poly(epsilon-caprolactone) crystals show the truncated lozenge-shaped morphology with clear striation lines. For the blends, the truncated lozenge-shaped morphology modified by bending to regular and/or inverted S- or C-shaped crystals with temperature, and the poly(vinyl methyl ether) composition in the blend. For a certain composition ratio of blend, with lowering the crystallization temperature, the bending of the crystals increases significantly. The band to bend morphology of the poly(epsilon-caprolactone) crystals is found strong dependence on the crystallization temperature, composition ratio of the blends, and the thickness of the film.