Interplay between solid state microstructure and photophysics for poly(9,9-dioctylfluorene) within oriented polyethylene hosts

Abstract

We present a study of isotropic and uniaxially oriented binary blend films comprising <1 wt % of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) dispersed in both ultrahigh molecular weight (UHMW) and linear-low-density (LLD) polyethylene (PE). Polarized absorption, fluorescence and Raman spectroscopy, scanning electron microscopy, and X-ray diffraction are used to characterize the samples before and after tensile deformation. Results show that blend films can be prepared with PFO chains adopting a combination of several distinct molecular conformations, namely glassy, crystalline, and the so-called β-phase, which directly influences the resulting optical properties. Both PFO concentration and drawing temperature strongly affect the alignment of PFO chains during the tensile drawing of the blend films. In both PE hosts, crystallization of PFO takes place during drawing; the resulting ordered chains show optimal optical anisotropy. Our results clarify the PFO microstructure in oriented blends with PE and the processing conditions required for achieving the maximal optical anisotropy.