Supramolecular Assemblies of a Semirigid Polyanion in Aqueous Solutions

Achieving High-Performance Lithium-Sulfur Batteries by Modulating Li+ Desolvation Barrier with Liquid Crystal Polymers

Lithium-sulfur (Li-S) batteries offer high theoretical capacity but are hindered by poor rate capability and cycling stability due to sluggish Li2S precipitation kinetics. Here a sulfonate-group-rich liquid crystal polymer (poly-2,2'-disulfonyl-4,4'-benzidine terephthalamide, PBDT) is designed and fabricated to accelerate Li2S precipitation by promoting the desolvation of Li+ from electrolyte. PBDT-modified separators are employed to assemble Li-S batteries, which deliver a remarkable rate capacity (761 mAh g-1 at 4 C) and cycling stability (500 cycles with an average decay rate of 0.088% per cycle at 0.5 C). A PBDT-based pouch cell even delivers an exceptional capacity of ≈1400 mAh g-1 and an areal capacity of ≈11 mAh cm-2 under lean-electrolyte and high-sulfur-loading condition, demonstrating promise for practical applications. Results of Raman spectra, molecular dynamic (MD) and density functional theory (DFT) calculations reveal that the abundant anionic sulfonate groups of PBDT aid in Li+ desolvation by attenuating Li+-solvent interactions and lowering the desolvation energy barrier. Plus, the polysulfide adsorption/catalysis is also excluded via electrostatic repulsion. This work elucidates the critical impact of Li+ desolvation on Li-S batteries and provides a new design direction for advanced Li-S batteries.

Bionic ordered structured hydrogels: structure types, design strategies, optimization mechanism of mechanical properties and applications

Natural organisms, such as lobsters, lotus, and humans, exhibit exceptional mechanical properties due to their ordered structures. However, traditional hydrogels have limitations in their mechanical and physical properties due to their disordered molecular structures when compared with natural organisms. Therefore, inspired by nature and the properties of hydrogels similar to those of biological soft tissues, researchers are increasingly focusing on how to investigate bionic ordered structured hydrogels and render them as bioengineering soft materials with unique mechanical properties. In this paper, we systematically introduce the various structure types, design strategies, and optimization mechanisms used to enhance the strength, toughness, and anti-fatigue properties of bionic ordered structured hydrogels in recent years. We further review the potential applications of bionic ordered structured hydrogels in various fields, including sensors, bioremediation materials, actuators, and impact-resistant materials. Finally, we summarize the challenges and future development prospects of bionic ordered structured hydrogels in preparation and applications.

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

We report on the morphology and mechanical properties of nanocomposite films derived from aqueous, hybrid liquid crystalline mixtures of rodlike aggregates of a sulfonated, all-aromatic polyamide, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), and graphene oxide (GO) platelets. An isothermal step at 200 °C facilitates in situ partial thermal reduction of GO to reduced GO (rGO) in nanocomposite films. X-ray scattering studies reveal that PBDT-rGO nanocomposites exhibit both higher in-plane alignment of PBDT (the order parameter increases from 0.79 to 0.9 at 1.8 vol % rGO) and alignment along the casting direction (from 0.1 to 0.6 at 1.8 vol % rGO). From dynamic mechanical thermal analysis, the interaction between PBDT and rGO causes the β-relaxation activation energy for PBDT to increase with rGO concentration. Modulus mapping of nanocomposites using atomic force microscopy demonstrates enhanced local stiffness, indicating reinforcement. From stress-strain analysis, the average Young's modulus increases from 16 to 37 GPa at 1.8 vol % rGO and the average tensile strength increases from 210 to 640 MPa. Despite polymer alignment along the casting direction, an average transverse tensile strength of 230 MPa is obtained.

Electrochemically-Obtained Polysulfonic-Acids Doped Polyaniline Films-A Comparative Study by Electrochemical, Microgravimetric and XPS Methods

Polyaniline (PANI) layers are electrochemically obtained in the presence of four polysulfonic acids with different rigidities of the polymer backbone-iso-(and tere-)poly-(4,4'-(2,2'-disulfonic acid)-diphenylene-iso(tere)-phthalamide (i-PASA and t-PASA), polystyrenesulfonic acid (PSSA) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA). Combined microgravimetric (EQCM) and electrochemical measurements are carried out in the course of polymerization and repetitive redox switching. It is found that after synthesis PASA-doped PANIs shows good stability with low exchange of mass in the course of voltammetric scans, while PAMPSA-doped PANI contains a large amount of water that gradually becomes expelled in the repetitive redox switching. PANI obtained in the presence of PSSA takes an intermediate position with respect to mass exchanged in the electrochemical redox process. XPS studies are used to obtain data for the extent of doping of the different PANI materials. The results show high doping level (about 0.5) for PASA- and PAMPSA- and lower level (0.32) for PSSA-doped PANI layers. Repeated electrochemical studies carried out with the specimens investigated by XPS after long-term storage in the dry state give evidence for structural rearrangement, perfect recuperation of the initial electrochemical activity and high stability of the electrochemical response.

Double helical conformation and extreme rigidity in a rodlike polyelectrolyte

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While double and multiple helix structures appear widely in nature, only rarely are these found in synthetic non-chiral macromolecules. Here we report a double helical conformation in the densely charged aromatic polyamide poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT. This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). We present X-ray diffraction, NMR spectroscopy, and molecular dynamics (MD) simulations that reveal and confirm the double helical conformation. The discovery of this extreme rigidity in combination with high charge density gives insight into the self-assembly of molecular ionic composites with high mechanical modulus (~ 1 GPa) yet with liquid-like ion motions inside, and provides fodder for formation of other 1D-reinforced composites.

Double helix structures appear widely in nature, but only rarely in synthetic non-chiral macromolecules. Here the authors describe a double helix in a densely charged aromatic polyamide, which exhibits an axial rigidity persistence length of ~ 1 μm, much higher than that of DNA (~ 50 nm).

Charged nanorods at heterogeneously charged surfaces

We study the spatial and orientational distribution of charged nanorods (rodlike counterions) as well as the effective interaction mediated by them between two plane-parallel surfaces that carry fixed (quenched) heterogeneous charge distributions. The nanorods are assumed to have an internal charge distribution, specified by a multivalent monopolar moment and a finite quadrupolar moment, and the quenched surface charge is assumed to be randomly distributed with equal mean and variance on the two surfaces. While equally charged surfaces are known to repel within the traditional mean-field theories, the presence of multivalent counterions has been shown to cause attractive interactions between uniformly charged surfaces due to the prevalence of strong electrostatic couplings that grow rapidly with the counterion valency. We show that the combined effects due to electrostatic correlations (caused by the coupling between the mean surface field and the multivalent, monopolar, charge valency of counterions) as well as the disorder-induced interactions (caused by the coupling between the surface disorder field and the quadrupolar moment of counterions) lead to much stronger attractive interactions between two randomly charged surfaces. The interaction profile turns out to be a nonmonotonic function of the intersurface separation, displaying an attractive minimum at relatively small separations, where the ensuing attraction can exceed the maximum strong-coupling attraction (produced by multivalent monopolar counterions between uniformly charged surfaces) by more than an order of magnitude.

A diffusion-driven fabrication technique for anisotropic tubular hydrogels

A bio-inspired, simple, and versatile diffusion-driven method to fabricate complex tubular hydrogels is reported. The controlled diffusion of small ions from a pre-designed core hydrogel through a biopolymer reservoir solution causes the self-gelation of biopolymers with an anisotropic ordered structure on the surface of the core hydrogel. By controlling the concentration, diffusion time, and flow direction of the ions, as well as the size and shape of the core, various types of complex tubular-shaped hydrogels with well-defined 3D architectures were fabricated. The mechanical properties of the designed alginate-based tubular hydrogels were highly tunable and comparable to those of native blood vessels. The method was applied to form a living-cell encapsulated tubular hydrogel, which further strengthens its potential for biomedical applications. The method is suitable for biopolymer-based reaction-diffusion systems and available for further research on the fabrication of functional biomaterials with various biopolymers.

Chiral lyotropic chromonic liquid crystals composed of disodium cromoglycate doped with water-soluble chiral additives

We investigated the pitches of cholesteric liquid crystals prepared by mixing disodium cromoglycate (DSCG) in water with 5 different water-soluble chiral additives. The measurements are based on the Grandjean-Cano wedge cell method. Overall, the twisting effect is weak, and the shortest pitch of 2.9 ± 0.2 μm is obtained using trans-4-hydroxy-l-proline, by which the cholesteric sample is iridescent at certain viewing angles. Freeze-fracture transmission electron microscopy (FFTEM) was also performed for the first time on both the nematic and cholesteric phases, revealing that stacked chromonic aggregates are very long, up to a few hundred nm, which explains why cholesteric chromonic liquid crystals hardly have pitches in the visible wavelength region.

Highly Conductive and Thermally Stable Ion Gels with Tunable Anisotropy and Modulus

A new liquid-crystalline ion gel exhibits unprecedented properties: conductivity up to 8 mS cm(-1) , thermal stability to 300 °C, and electrochemical window to 6.1 V, as well as adjustable transport anisotropy (up to 3.5×) and elastic modulus (0.03-3 GPa). The combination of ionic liquid and magnetically oriented rigid-rod polyanion provides widely tunable properties for use in diverse electrochemical devices.