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A series of sulfonate polyester ionomers with well-defined poly(ethylene oxide) spacer lengths between phthalates and alkali metal cations as counterions are designed for improved ionic conductivity. Ion conduction in these chemically complex materials is dominated by the polymer mobility and the state of ionic aggregation. While the aggregation decreases dramatically at room temperature as the cation size increases from Li to Na to Cs, the extents of ionic aggregation of these ionomers are comparable at elevated temperatures. Both the Na and Cs ionomers exhibit thermally reversible transformation upon heating from 25 to 120 °C as isolated ion pairs aggregate. This seemingly counterintuitive aggregation of ions on heating is driven by the fact that the dielectric constant of all polar liquids decreases on heating, enhancing Coulomb interactions between ions.

We study a unique biomaterial developed from fungal mycelium, the vegetative part and the root structure of fungi. Mycelium has a filamentous network structure with mechanics largely controlled by filament elasticity and branching, and network density. We report the morphological and mechanical characterization of mycelium through an integrated experimental and computational approach. The monotonic mechanical behavior of the mycelium is non-linear both in tension and compression. The material exhibits considerable strain hardening before rupture under tension, it mimics the open cell foam behavior under compression and exhibits hysteresis and the Mullins effect when subjected to cyclic loading. Based on our morphological characterization and experimental observations, we develop and validate a multiscale fiber network-based model for the mycelium which reproduces the tensile and compressive behavior of the material.

A series of Li-, Na-, and Cs-neutralized polyester ionomers with well-defined poly(ethylene oxide) (PEO) spacer lengths between sulfonated phthalates have been investigated by X-ray scattering at room temperature. As the spacer lengths are increased the PEO segments crystallize, as evidenced by multiple crystal reflections that are identical to those of pure poly(ethylene glycol) oligomers. This crystallization also produces multiple small-angle peaks, which correspond to the well-defined thickness of PEO crystallites. The ionomer peak (q=1-5 nm -1 ) is absent in the Na-and Cs-neutralized ionomers, while the Li-neutralized ionomers show peaks at q = 2-3 nm -1 , reminiscent of conventional ionic aggregates in ionomers. Detailed analysis of the normalized X-ray scattering intensity from these ionomers reveals a variety of ionic states that are highly dependent on the cation size. The states of ionic groups change from a majority of isolated ion pairs to aggregated structures as the cation size decreases from Cs to Li. These findings compare favorably with ab initio calculations.

Conventional sodium cations (Na+) in sulfonated polyester ionomers were replaced with ammonium-based ionic liquid counterions. Counterion dynamics were measured by dielectric spectroscopy and linear viscoelastic response via oscillatory shear. Ion exchange from sodium counterions to ionic liquid counterions such as tetramethylammonium and tetrabutylammonium showed an order of 104 increase in conductivity compared with sodium counterions, primarily attributed to weaker ionic interactions that lower the glass transition temperature. Electrode polarization was used in conjunction with the 1953 Macdonald model to determine the number density of conducting counterions and their mobility. Conductivity and mobility exhibit Vogel−Fulcher−Tammann (VFT) temperature dependences and both increased with counterion size. Conducting counterion concentrations showed Arrhenius temperature dependences, with activation energy reduced as counterion size increased. When ether−oxygen was incorporated into the mobile cation structure, self-solvating ability notably increased the conducting ion concentration. Weakened ion pairing interactions prove favorable for fundamental design of single-ion conductors for actuators, as ionic liquid counterions can provide both larger and faster strains, required by such electro-active devices.

Poly­(ethylene oxide) [PEO] ionomers are candidate materials for electrolytes in energy storage devices due to the ability of ether oxygen atoms to solvate cations. Copolyester ionomers are synthesized via condensation of sulfonated phthalates with glycol mixtures of PEO and poly­(tetramethylene oxide) [PTMO] to create random copolymer ionomers with nearly identical ion content and systematically varying solvation ability. Variation of the PEO/PTMO composition leads to changes in T g, dielectric constant and ionic aggregation; each with consequences for ion transport. Dielectric spectroscopy is used to determine number density of conducting ions, their mobility, and extent of aggregation. Conductivity and mobility display Vogel temperature dependence and increase with PEO content; despite the lower T g of PTMO. Conducting ion densities show Arrhenius temperature dependence and are nearly identical for all copolymer ionomers that contain PEO. SAXS confirms the extent of aggregation, corroborates the temperature response from dielectric measurements, and reveals microphase separation into a PTMO-rich microphase and a PEO-rich microphase that contains the majority of the ions. The trade-off between ion-solvation and low T g in this study provides fundamental understanding of ionic aggregation and ion transport in polymer single-ion conductors.

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