1 research outputs found
Ion Transport and Interfacial Dynamics in Disordered Block Copolymers of Ammonium-Based Polymerized Ionic Liquids
A series
of diblock copolymers bearing a polymerized ionic liquid
(polyIL) block (poly(<i>N</i>-(methacryloyloxy)ethyl-<i>N</i>,<i>N</i>-dimethyl-<i>N</i>-ethylammonium
bis(trifluoromethylsulfonyl)imide)) and a noncharged block (poly(methyl
methacrylate) (PMMA)) or poly(<i>n</i>-butyl methacrylate)
(PBuMA)) were studied using differential scanning calorimetry (DSC),
small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS),
and broadband dielectric spectroscopy (BDS) to probe the effect of
ion concentration on the morphology and ion transport in these polyelectrolytes.
Two majority PMMA block copolymers, having mole ratios of the polyIL
of 0.19 and 0.22, exhibited evidence of aggregation indicated by interfacial
polarization in the dielectric spectra. The 0.19 mole ratio sample
also displayed two distinct glass transitions by DSC. The SAXS measurements
showed that no long-range order was present in these samples. The
ionic conductivity of these samples were lower than the polyIL homopolymer
due to hindered ion transport at the aggregate boundaries. Copolymers
with majority polyIL blocks were found to exhibit disorder based on
SAXS and DSC measurements. Furthermore, at a mole fraction of 0.91
of the polyIL the ionic conductivity was enhanced by a factor of ca.
1.5 with respect to the polyIL homopolymer, with a similar increase
observed for the static dielectric permittivity. The effective number
density and mobility of the ions were calculated for these systems
from BDS and WAXS data, indicating that the enhancement of the ionic
conductivity corresponds to an increase in the density of mobile charge
carriers. The higher effective number density of charge carriers correlates
with increased static dielectric permittivity, suggesting that ion
pair dissociation is the likely mechanism behind the observed enhancement
of ion transport. This study showcases the wealth of information that
can be obtained from a combination of complementary experimental techniques