Morphological selectivity of the films of linear and star-shaped poly (ε-caprolactone)

Abstract

Films created by poly (e-caprolactone) (PCL) have made a lot of consideration in biomedical applications because of their biodegradability, biocompatibility, incredible flexibility, and nontoxic degradation by-products. In this study, switching behavior of surface morphology of linear and star-shaped PCL as a function of polarity of the substrate, molecular weight of the polymer, solvent vapor annealing, solvent annealing, and thermal annealing were investigated. Films of PCL were prepared by drop casting method and their morphology was visualized through atomic force microscopy (AFM). Although, the whole study is based on AFM imaging, some of the basic morphologies of PCL films as obtained by AFM are also compared with SEM and TEM analysis. The substantial difference in polarity and roughness of mica and silicon wafers leads to different chain orientation of the polymer chains. Morphology transition strongly depends on the molecular weight of the polymer, low molar mass PCL presented larger surface domains compared to their higher molar mass analogs. Annealing of polymer with THF and ethanol vapors has improved the long-range ordering of PCL chains, while hexane and water vapors led to swelling of the films. The morphology of the film has also shown selectivity for the casting solvent. Thermal annealing around the melting temperature of the PCL made polymeric chains more extended and uniformly oriented.