Miscibility,Crystallization, and Morphology of the Double-Crystalline Blends of Insulating Polyethylene and Semiconducting Poly(3-Butylthiophene)

A series of crystalline semiconducting poly(3-butylthiophene) (P3BT)/crystalline insulating polyethylene (PE) blends were prepared and the miscibility, crystallization, and structure/morphology were investigated. Even though phase separation was observed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), several pieces of evidence indicated that limited miscibility should be present in PE/P3BT blends: small changes in both T_m and crystallinity of PE phase and a small portion of PE being dissolved in P3BT. The study of PE isothermal crystallization kinetics revealed that the introduction of P3BT significantly influenced the nucleation mechanism and growth geometry, i.e., PE was transformed from three-dimensional (3D) spherulitic to two-dimensional (2D) disc crystals. A striking reduction of nucleation density and an obvious ringed morphology of PE spherulites (2D) in PE/P3BT blends were also observed by polarized optical microscopy; it is proposed that the limited miscibility between PE and crystalline P3BT favors the formation of ringed PE spherulite in the blends. Additionally, preferred orientation of PE lamellae, with their b-axis largely constrained to the thin film plane, was observed by X-ray diffraction in PE/P3BT blend films. It is evidenced that the PE orientation was due to the b-axis being the crystal growth direction, which can only be in film plane.