Fabrication of compositional-gradient biodegradable polymeric films showing self-bending deformation

A compositional graded film of poly(ε-caprolactone) (PCL) with 4,4'-thiodiphenol (TDP), in the film thickness direction, was fabricated by self-diffusing of TDP in the PCL melt. We found out the self-bending deformation of the gradient film, which bent into a rolled-up shape by itself. The initial shape of the film was flat when the sample was quenched from the melt. Upon the fast crystallization of PCL, the gradient film bent to the side with low TDP content. Then, after PCL crystallized the film bent to the opposite direction, that is, to the side with high TDP content. This bending to the TDP rich region was induced by not only the crystallization of PCL but also mass transfer due to the diffusion of TDP from TDP rich region to poor region.