No abstract

Materials exhibiting high dielectric constants (𝜀𝜀 𝑠𝑠 ) are critical for energy storage and actuators. A successful approach to increase 𝜀𝜀 𝑠𝑠 by incorporating polar additives (with high 𝜀𝜀 𝑠𝑠 ) but controlling the resulting dispersion state is difficult. Here, we show that significant 𝜀𝜀 𝑠𝑠 increases are realized by adding zwitterions, which are small molecules with a cation and an anion separated by covalent bonds. The increase in 𝜀𝜀 𝑠𝑠 with zwitterion addition is attributed to the large molecular dipole of zwitterions, ranging from 35 to 41 Debye, as experimentally quantified, and confirmed using density functional theory. At elevated zwitterion concentration in an ethylene glycol medium, there is a non-linear increase of 𝜀𝜀 𝑠𝑠 that eventually saturates due to the strong Coulombic interactions between zwitterions. The presented work provides a fundamental molecular understanding of why zwitterions are effective additives in boosting 𝜀𝜀 𝑠𝑠 in soft materials.

This study investigates the charge-transport properties of poly(3hexylthiophene-2,5-diyl) (P3HT) and poly(ProDOT-alt-biEDOT) (PE 2 ) films doped with a set of iron(III)-based dopants and as a function of dopant concentration. X-ray photoelectron spectroscopy measurements show that doping P3HT with 12 mM iron(III) solutions leads to similar extents of oxidation, independent of the dopant anion; however, the electrical conductivities and Seebeck coefficients vary significantly (5 S cm −1 and + 82 μV K −1 with tosylate and 56 S cm −1 and +31 μV K −1 with perchlorate). In contrast, PE 2 thermoelectric transport properties vary less with respect to the iron(III) anion chemistry, which is attributed to PE 2 having a lower onset of oxidation than P3HT. Consequentially, PE 2 doped with 12 mM iron(III) perchlorate obtained an electrical conductivity of 315 S cm −1 and a Seebeck coefficient of + 7 μV K −1 . Modeling these thermoelectric properties with the semilocalized transport (SLoT) model suggests that tosylate-doped P3HT remains mostly in the localized transport regime, attributed to more disorder in the microstructure. In contrast perchlorate-doped P3HT and PE 2 films exhibited thermally deactivated electrical conductivities and metal-like transport at high doping levels over limited temperature ranges. Finally, the SLoT model suggests that PE 2 has the potential to be more electrically conductive than P3HT due to PE 2 's ability to achieve higher extents of oxidation and larger shifts in the reduced Fermi energy levels.

Herein, a route to produce highly electrically conductive doped hydroxymethyl functionalized poly(3,4‐ethylenedioxythiophene) (PEDOT) films, termed PEDOT(OH) with metal‐like charge transport properties using a fully solution processable precursor polymer is reported. This is achieved via an ester‐functionalized PEDOT derivative [PEDOT(EHE)] that is soluble in a range of solvents with excellent film‐forming ability. PEDOT(EHE) demonstrates moderate electrical conductivities of 20–60 S cm−1 and hopping‐like (i.e., thermally activated) transport when doped with ferric tosylate (FeTos3). Upon basic hydrolysis of PEDOT(EHE) films, the electrically insulative side chains are cleaved and washed from the polymer film, leaving a densified film of PEDOT(OH). These films, when optimally doped, reach electrical conductivities of ≈1200 S cm−1 and demonstrate metal‐like (i.e., thermally deactivated and band‐like) transport properties and high stability at comparable doping levels.

Creating polymers that exhibit a switchable thermal conductivity requires a fundamental understanding of how polymer structure and inter- and intramolecular interactions influence thermal transport. To develop this fundamental understanding, we synthesize a series of precursor un-cross-linked statistical copolymers with varying mole fractions of furan functional groups via reversible-addition fragmentation chain transfer (RAFT) polymerization. These precursor polymers, containing the furan diene, were then cross-linked using a reversible Diels–Alder cycloaddition to form dynamic covalent networks of varying cross-link densities. Furthermore, two separate dienophile cross-linkers were used to investigate how the molecular weight and length of the cross-linker influence the mechanical and thermal properties of the network. Counter to some recent theoretical studies, we found that both the elastic modulus and thermal conductivity were largely unaffected by the extent of cross-linking and the structure of the cross-linker. For this system, the Diels–Alder reaction was also found to be slow in the solid state, further limiting its utility as a thermal conductivity switch.