Molecular Dynamics and Charge Transport in Polymeric Polyisobutylene-Based Ionic Liquids

Abstract

A homologous series of 16 polymeric ionic liquids (PIL) are investigated based on monovalent and bivalent telechelic polyisobutylene (PIB) carrying the ionic liquid (IL)-like cationic headgroup ( N, N, N -triethylammonium or 1-methylpyrrolidinium) and Br, NTf 2, OTf, or pTOS as anions. Molecular dynamics, charge transport, and polarization at mesoscopic scales are analyzed over a wide frequency (10 –2 –10 7 Hz) and temperature (200–400 K) range by means of broadband dielectric spectroscopy (BDS); additionally, differential scanning calorimetry (DSC) is employed. In detail, (i) three molecular relaxation processes are observed including the dynamic glass transition of the polymeric matrix, (ii) a conductivity relaxation originating from charge transport in the IL-like moieties, and (iii) a weak electrode polarization caused by the accumulation of mobile charge carriers at the metal interfaces. The net conductivity of the PIL as a whole is quantitatively described by an effective-medium approximation (EMA) reflecting the microphase-separated character of the PIL under study.