Sulfonated polyoxadiazole synthesis and processing into ion‐conducting films

Alkylbenzoic and Alkyloxybenzoic Acid Blending for Expanding the Liquid Crystalline State and Improving Its Rheology

Thermotropic mesogens typically exist as liquid crystals (LCs) in a narrow region of high temperatures, making lowering their melting point with the temperature expansion of the mesophase state an urgent task. Para-substituted benzoic acids can form LCs through noncovalent dimerization into homodimers via hydrogen bonds, whose strength and, consequently, the temperature region of the mesophase state can be potentially altered by creating asymmetric heterodimers from different acids. This work investigates equimolar blends of p-n-alkylbenzoic (kBA, where k is the number of carbon atoms in the alkyl radical) and p-n-alkyloxybenzoic (kOBA) acids by calorimetry and viscometry to establish their phase transitions and regions of mesophase existence. Non-symmetric dimerization of acids leads to the extension of the nematic state region towards low temperatures and the appearance of new monotropic and enantiotropic phase transitions in several cases. Moreover, the crystal-nematic and nematic-isotropic phase changes have a two-step character for some acid blends, suggesting the formation of symmetric and asymmetric associates from heterodimers. The mixing of 6BA and 8OBA most strongly extends the region of the nematic state towards low temperatures (from 95-114 °C and 108-147 °C for initial homodimers, respectively, to 57-133 °C for the resulting heterodimer), whereas the combination of 4OBA and 5OBA gives the most extended high-temperature nematic phase (up to 156 °C) and that of 6BA and 9OBA (or 12OBA) provides the existence of a smectic phase at the lowest temperatures (down to 51 °C).

Self-Lubricating and Shape-Stable Phase-Change Materials Based on Epoxy Resin and Vegetable Oils

Palm or coconut oil is capable of dissolving in a mixture of bisphenol A-based epoxy resin and a high-temperature hardener (4,4'-diaminodiphenyl sulfone) when heated and then forms a dispersed phase as a result of cross-linking and molecular weight growth of the epoxy medium. Achieving the temporary miscibility between the curing epoxy matrix and the vegetable oil allows a uniform distribution of vegetable oil droplets in the epoxy medium. This novel approach to creating a dispersed phase-change material made a cured epoxy polymer containing up to 20% oil. The miscibility of epoxy resin and oil was studied by laser interferometry, and phase state diagrams of binary mixtures were calculated according to theory and experiments. A weak effect of oil on the viscosity and kinetics of the epoxy resin curing was demonstrated by rotational rheometry. According to differential scanning calorimetry and dynamic mechanical analysis, the oil plasticizes the epoxy matrix slightly, expanding its glass transition region towards low temperatures and reducing its elastic modulus. In the cured epoxy matrix, oil droplets have a diameter of 3-14 µm and are incapable of complete crystallization due to their multi-component chemical composition and non-disappeared limited miscibility. The obtained phase-change materials have relatively low specific energy capacity but can be used alternatively as self-lubricating low-noise materials due to dispersed oil, high stiffness, and reduced friction coefficient. Palm oil crystallizes more readily, better matching the creation of phase-change materials, whereas coconut oil crystallization is more suppressed, making it better for reducing the friction coefficient of the oil-containing material.

The Effect of Non-Solvent Nature on the Rheological Properties of Cellulose Solution in Diluted Ionic Liquid and Performance of Nanofiltration Membranes

The weak point of ionic liquids is their high viscosity, limiting the maximum polymer concentration in the forming solutions. A low-viscous co-solvent can reduce viscosity, but cellulose has none. This study demonstrates that dimethyl sulfoxide (DMSO), being non-solvent for cellulose, can act as a nominal co-solvent to improve its processing into a nanofiltration membrane by phase inversion. A study of the rheology of cellulose solutions in diluted ionic liquids ([EMIM]Ac, [EMIM]Cl, and [BMIM]Ac) containing up to 75% DMSO showed the possibility of decreasing the viscosity by up to 50 times while keeping the same cellulose concentration. Surprisingly, typical cellulose non-solvents (water, methanol, ethanol, and isopropanol) behave similarly, reducing the viscosity at low doses but causing structuring of the cellulose solution and its phase separation at high concentrations. According to laser interferometry, the nature of these non-solvents affects the mass transfer direction relative to the forming membrane and the substance interdiffusion rate, which increases by four-fold when passing from isopropanol to methanol or water. Examination of the nanofiltration characteristics of the obtained membranes showed that the dilution of ionic liquid enhances the rejection without changing the permeability, while the transition to alcohols increases the permeability while maintaining the rejection.

N-Type Polyoxadiazole Conductive Polymer Binders Derived High-Performance Silicon Anodes Enabled by Crosslinking Metal Cations

The dilemma of employing high-capacity battery materials and maintaining the electrodes' electrical and mechanical integrity requires a unique binder system design. Polyoxadiazole (POD) is an n-type conductive polymer with excellent electronic and ionic conductive properties, which has acted as a silicon binder to achieve high specific capacity and rate performance. However, due to its linear structure, it cannot effectively alleviate the enormous volume change of silicon during the process of lithiation/delithiation, resulting in poor cycle stability. This paper systematically studied metal ion (i.e., Li⁺, Na⁺, Mg²⁺, Ca²⁺, and Sr²⁺)-crosslinked PODs as silicon anode binders. The results show that the ionic radius and valence state remarkably influence the polymer's mechanical properties and the electrolyte's infiltration. Electrochemical methods have thoroughly explored the effects of different ion crosslinks on the ionic and electronic conductivity of POD in the intrinsic and n-doped states. Attributed to the excellent mechanical strength and good elasticity, Ca-POD can better maintain the overall integrity of the electrode structure and conductive network, significantly improving the cycling stability of the silicon anode. The cell with such binders still retains a capacity of 1770.1 mA h g^-1 after 100 cycles at 0.2 C, which is ∼285% that of the cell with the PAALi binder (620.6 mA h g^-1). This novel strategy using metal-ion crosslinking polymer binders and the unique experimental design provides a new pathway of high-performance binders for next-generation rechargeable batteries.

Non-Solvent- and Temperature-Induced Phase Separations of Polylaurolactam Solutions in Benzyl Alcohol as Methods for Producing Microfiltration Membranes

The possibility of obtaining porous films through solutions of polylaurolactam (PA12) in benzyl alcohol (BA) was considered. The theoretical calculation of the phase diagram showed the presence of the upper critical solution temperature (UCST) for the PA12/BA system at 157 °C. The PA12 completely dissolved in BA at higher temperatures, but the resulting solutions underwent phase separation upon cooling down to 120–140 °C because of the PA12’s crystallization. The viscosity of the 10–40% PA12 solutions increased according to a power law but remained low and did not exceed 5 Pa·s at 160 °C. Regardless of the concentration, PA12 formed a dispersed phase when its solutions were cooled, which did not allow for the obtention of strong films. On the contrary, the phase separation of the 20–30% PA12 solutions under the action of a non-solvent (isopropanol) leads to the formation of flexible microporous films. The measurement of the porosity, wettability, strength, permeability, and rejection of submicron particles showed the best results for a porous film produced from a 30% solution by non-solvent-induced phase separation. This process makes it possible to obtain a membrane material with a 240 nm particle rejection of 99.6% and a permeate flow of 1.5 kg/m2hbar for contaminated water and 69.9 kg/m2hbar for pure water.

Effect of Hydrogen Bonding on Dynamic Rheological Behavior of PVA Aqueous Solution

The rheological behavior of polyvinyl alcohol (PVA) aqueous solution is crucial to optimizing the processing technology and performance of PVA products. In this paper, the dynamic rheological behavior of PVA aqueous solution was investigated in detail. PVA solution with a concentration of 10 wt% showed unnormal rheological behaviors, that is, the liquid-like behavior in the high frequency (ω) region and the solid-like behavior in the low ω region. A storage modulus (G′) plateau appears in the relatively low ω region as a gel with a network structure. Different from conventional hydrogel, this plateau has a low modulus, and the corresponding size of the relaxation unit is estimated to be 554 nm, being higher than the size of a whole PVA chain. It is believed that the network mesh is formed by the intermolecular hydrogen bonding interactions among PVA chains. The relaxation time of these meshes is longer than the reptation time of a PVA chain. Based on the relaxation spectrum and calculation analysis, it is found that the destruction of intermolecular hydrogen bonds, such as by heating up, adding sodium dodecyl sulfate, and shear operation, will make the relaxation unit (mesh) larger and lead to the left shift of the intersection of G′ and loss modulus (G″). In a PVA solution with a high concentration, multiple meshes of various sizes could be formed and thus generate multiple relaxation peaks. The large-sized meshes mainly contribute to the left shift of the intersection of G′ and G″, and the small-sized meshes contribute to the high plateau modulus. The results in this paper offer a new angle to analyze polymer solutions with strong intermolecular interaction.