Fabrication of functionally graded bulk materials of organic polymer blends by uniaxial thermal gradient

Compositionally graded bulk materials of organic polymer blends were prepared by using nonequilibrium self-organization processes with a uniaxial thermal gradient (Bridgman method). The Bridgman method was firstly applied to prepare two kinds of polymeric compositionally graded materials: a polymer/low molecular weight additive system (poly(e-caprolactone) (PCL)/ 4,49-thiodiphenol (TDP)) and a polymer/polymer system (PCL/poly(ethylene oxide) (PEO)). In the PCL/TDP system, the content of TDP was decreased with respect to the solidification direction. From variable temperature FT-IR measurements, it was found that the amount of hydrogen bonding between PCL and TDP continuously increased with decreasing temperature, suggesting that the TDP molecules were captured by PCL with hydrogen bonding on the lower temperature side of thermal gradient. The crystallinity of PCL in the Bridgman sample increases in the solidification direction, indicating that more TDP molecules were trapped at an earlier stage of solidification. In the PCL/PEO system, the content of PEO decreased with respect to the solidification direction. The PCL molecules were excluded from the solidification surface to the liquid region, which is due to the higher crystallization temperature of PEO than that of PCL. This means that the PCL molecules can diffuse from the solidification interface to the liquid phase. The simple technique using a uniaxial thermal gradient provides a new way to fabricate polymeric functionally graded bulk materials.