Dielectric Spectroscopy of Polystyrene/Poly(ethylene oxide) Composites

Abstract

Dielectric spectra of composites of poly(ethylene oxide), PEO, in polystyrene, PS, have been obtained, as a function of frequency and temperature. The dispersion of a high-dielectric constant, low-glass transition temperature, semicrystalline polymer (PEO) in an amorphous, lower dielectric constant, high-Tg continuum (PS) has enabled the dielectric observation of four molecular relaxation processes in PEO. They are the α relaxation associated with the crystalline melt of PEO; two WLF type relaxations, β and β‘, which we speculate to be respectively associated with the onset of segmental motion and free-volume expansion of unrestricted amorphous PEO chains and with amorphous PEO chain segments tethered in crystallites; and a sub-Tg, γ relaxation associated with localized motions in the crystalline chain segments. The relaxations associated with the α and β‘ processes have not been previously observed dielectrically. In pure, neat PEO, the α and β‘ relaxations are obscured by dc losses. The dispersion of PEO as micron-sized and submicron phases in PS enables its full relaxation spectrum to be observed.