The conductivity enhancement in solvent treated PEDOT:PSS is a result of the solvation of the PSS shell, leading to the release of conductive PEDOT in the core.
Hydrated polyelectrolyte (PE) complexes and multilayers undergo a well-defined thermal transition that bears resemblance to a glass transition. By combining molecular simulations and differential scanning calorimetry (DSC) of poly(diallyldimethylammonium) (PDAC) and poly(styrenesulfonate) (PSS) multilayers, we establish for the first time that dehydration drives the thermally induced change in plasticization of the complex and in the diffusion behavior of its components. DSC experiments show that the thermal transition appears when the assemblies are hydrated in water, but not in the presence of alcohols, which supports that water is required for this transition. These findings connect PE complexes more generally to thermoresponsive polymers and liquid crystal phases, which bear phase transitions driven by the (de)hydration of functional groups, thus forming a fundamental link toward an integrated understanding of the thermal response of molecular materials in aqueous environments.
Polyelectrolyte complexes (PECs) form by mixing polycation and polyanion solutions together, and have been explored for a variety of applications. One challenge for PEC processing and application is that under certain conditions the as-formed PECs aggregate and precipitate out of suspension over the course of minutes to days. This aggregation is governed by several factors such as electrostatic repulsion, van der Waals attractions, and hydrophobic interactions. In this work, we explore the boundary between colloidally stable and unstable complexes as it is influenced by polycation/polyanion mixing ratio and ionic strength. The polymers examined are poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate) (PSS). Physical properties such as turbidity, hydrodynamic size, and zeta potential are investigated upon complex formation. We also perform detailed molecular dynamics simulations to examine the structure and effective charge distribution of the PECs at varying mixing ratios and salt concentrations to support the experimental findings. The results suggest that the colloidally stable/unstable boundary possibly marks the screening effects from added salt, resulting in weakly charged complexes that aggregate. At higher salt concentrations, the complexes initially form and then gradually dissolve into solution.
Hybrid (organic-inorganic) materials have emerged as a promising class of thermoelectric materials, achieving power factors (S2σ) exceeding those of either constituent. The mechanism of this enhancement is still under debate, and pinpointing the underlying physics has proven difficult. In this work, we combine transport measurements with theoretical simulations and first principles calculations on a prototypical PEDOT:PSS-Te(Cux) nanowire hybrid material system to understand the effect of templating and charge redistribution on the thermoelectric performance. Further, we apply the recently developed Kang-Snyder charge transport model to show that scattering of holes in the hybrid system, defined by the energy-dependent scattering parameter, remains the same as in the host polymer matrix; performance is instead dictated by polymer morphology manifested in an energy-independent transport coefficient. We build upon this language to explain thermoelectric behavior in a variety of PEDOT and P3HT based hybrids acting as a guide for future work in multiphase materials.
The conceptual understanding of charge transport in conducting polymers is still ambiguous due to a wide range of paracrystallinity (disorder). Here, we advance this understanding by presenting the relationship between transport, electronic density of states and scattering parameter in conducting polymers. We show that the tail of the density of states possesses a Gaussian form confirmed by two-dimensional tight-binding model supported by Density Functional Theory and Molecular Dynamics simulations. Furthermore, by using the Boltzmann Transport Equation, we find that transport can be understood by the scattering parameter and the effective density of states. Our model aligns well with the experimental transport properties of a variety of conducting polymers; the scattering parameter affects electrical conductivity, carrier mobility, and Seebeck coefficient, while the effective density of states only affects the electrical conductivity. We hope our results advance the fundamental understanding of charge transport in conducting polymers to further enhance their performance in electronic applications.
P-doping of conjugated
polymers requires electron transfer from
the conjugated polymer to the p-dopant. This implies that the highest
occupied molecular orbital (HOMO) of the conjugated polymer has to
be higher than the lowest unoccupied molecular orbital (LUMO) of the
p-dopant. Although commonly used p-dopants such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane
(F4TCNQ) have a low LUMO of −5.24 eV, most conjugated polymers
used in high-performance field-effect transistors are donor–acceptor-type
polymers with deep HOMO values, making them difficult to be effectively
doped by F4TCNQ. Here, we utilized the proquinoidal 2,6-dialkyl-benzo[1,2-d;4,5-d′]bistriazole (BBTa26) moiety
in conjugated polymers to destabilize HOMO, allowing effective p-doping
using very dilute F4TCNQ solutions. The extent of the quinoidal character
and hence their intrinsic conductivities and the ability to be doped
are dependent on the dihedral angles and aromaticity of the aryl spacer
groups along the polymer backbone. Intrinsic conductivities as high
as 10–2 S cm–1 were achieved.
Upon doping using F4TCNQ, highly delocalized polarons were observed.
As such, electrical conductivities of over 100 S cm–1 and an enhancement of the Seebeck coefficient from carrier-induced
softening can be achieved. A maximum power factor of 11.8 μW
m–1 K–2 was achieved in thin-film
thermoelectric devices. These results are among the highest for solution-phase
p-doping using F4TCNQ without additional processing.
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