High-Strength Liquid Crystal Polymer-Graphene Oxide Nanocomposites from Water

Synthetic Reversible Fibrous Network Hydrogels Based on a Double-Helical Polyelectrolyte

The unique mechanical properties of fibrous networks in biological tissues have inspired the development of synthetic fibrous network hydrogels, yet few polymers can reversibly form such structures. Here, we report the first reversible fibrous network hydrogel composed of synthetic polyelectrolytes with extremely rigid conformation (persistence length is ∼1 µm), made up of double-helical poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) and tetrabutylphosphonium bromide ([P4444]Br). The hydrogel exhibits a unique sol-gel transition, triggered by the hydrophobicity increase of [P4444]Br above lower critical solution temperature (LCST). This drives PBDT aggregation into fibrous bundles through electrostatic interactions. These bundles grow and branch into a continuous network, with the molecular rigidity of PBDT's double-helix conformation being key to gel formation. The hydrogel displays strain-stiffening mechanical responses akin to biological systems and shows a significant hysteresis (21 °C) between heating and cooling cycles. Uniquely, the effects of salts on the transition temperature deviate from the Hofmeister series, highlighting coordination with sulfonate groups as the dominant factor. Leveraging its modulus change during gelation, the hydrogel was successfully applied as a spray coating on superhydrophobic vertical Teflon surfaces. This study broadens the scope of thermoreversible hydrogels introducing gelation mechanisms for rigid polyelectrolytes and demonstrates their potential in advanced coatings.

Effect of Water-Soluble Polymers on the Rheology and Microstructure of Polymer-Modified Geopolymer Glass-Ceramics

This work explores the effects of rigid (0.1, 0.25, and 0.5 wt. %) and semi-flexible (0.5, 1.0, and 2.5 wt. %) all-aromatic polyelectrolyte reinforcements as rheological and morphological modifiers for preparing phosphate geopolymer glass-ceramic composites. Polymer-modified aluminosilicate-phosphate geopolymer resins were prepared by high-shear mixing of a metakaolin powder with 9M phosphoric acid and two all-aromatic, sulfonated polyamides. Polymer loadings between 0.5-2.5 wt. % exhibited gel-like behavior and an increase in the modulus of the geopolymer resin as a function of polymer concentration. The incorporation of a 0.5 wt. % rigid polymer resulted in a three-fold increase in viscosity relative to the control phosphate geopolymer resin. Hardening, dehydration, and crystallization of the geopolymer resins to glass-ceramics was achieved through mold casting, curing at 80 °C for 24 h, and a final heat treatment up to 260 °C. Scanning electron microscopy revealed a decrease in microstructure porosity in the range of 0.78 μm to 0.31 μm for geopolymer plaques containing loadings of 0.5 wt. % rigid polymer. Nano-porosity values of the composites were measured between 10-40 nm using nitrogen adsorption (Brunauer-Emmett-Teller method) and transmission electron microscopy. Nanoindentation studies revealed geopolymer composites with Young's modulus values of 15-24 GPa and hardness values of 1-2 GPa, suggesting an increase in modulus and hardness with polymer incorporation. Additional structural and chemical analyses were performed via thermal gravimetric analysis, Fourier transform infrared radiation, X-ray diffraction, and energy dispersive spectroscopy. This work provides a fundamental understanding of the processing, microstructure, and mechanical behavior of water-soluble, high-performance polyelectrolyte-reinforced geopolymer composites.

Mechanically and Thermally Robust Gel Electrolytes Built from A Charged Double Helical Polymer

Polymer electrolytes have received tremendous interest in the development of solid-state batteries, but often fall short in one or more key properties required for practical applications. Herein, a rigid gel polymer electrolyte prepared by immobilizing a liquid mixture of a lithium salt and poly(ethylene glycol) dimethyl ether with only 8 wt% poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) is reported. The high charge density and rigid double helical structure of PBDT lead to formation of a nanofibrillar structure that endows this electrolyte with stronger mechanical properties, wider temperature window, and higher battery rate capability compared to all other poly(ethylene oxide) (PEO)-based electrolytes. The ion transport mechanism in this rigid polymer electrolyte is systematically studied using multiple complementary techniques. Li/LiFePO4 cells show excellent capacity retention over long-term cycling, with thermal cycling reversibility between ambient temperature and elevated temperatures, demonstrating compelling potential for solid-state batteries targeting fast charging at high temperatures and slower discharging at ambient temperature.