Abstract:

Crystalline morphologies and molecular orientation of poly(ε-caprolactone)(PCL) thin films were investigated by means of combination of microscopic and spectroscopic methods. The PCL films with different thicknesses were prepared on Si and Al substrate by spin-coating. Atomic force microscopy(AFM) observations reveal that for the PCL films with thickness of ca. 200 nm and thicker than it, crystallization occurs preferentially in the form of edge-on lamellar crystals, whereas for thinner films, nucleated edge-on lamellar crystals become to rotate with some tilt angles, and with further decreasing film thickness, lamellae prefer into the plane of the film and grow as flat-on lamellae, which led to a preferred orientation of the PCL main chain axis perpendicular to the surface of the substrate. In addition, there is a dendritic crystal morphology formed when the film thickness is ca. 15 nm. The mean orientation of the polymer molecules in the  films was measured by polarized ATR-FTIR(attenuated total reflection-Fourier transform infrared) spectroscopy, and the results of the polarized ATR-FTIR  correspond to the AFM observations mentioned above. Those phenomena were discussed under a diffusion-limitation crystallization condition in PCL thin films.

Key words: PCL thin films; Crystalline morphology; Molecular orientation; AFM; Polarized ATR-FTIR