Synthesis and characterization of proton conductive liquid crystals bearing phosphonic acid moieties

Cyclodextrin-based liquid crystals: A novel approach to promote the formation of thermotropic cubic mesophases and their potential applications as electrolytes

We report the synthesis and mesomorphic studies of a family of amphiphilic β-cyclodextrin derivatives that are polyesterified at the secondary face with either 14 lauroyl or 14 stearoyl chains (apolar), and 7 tri- or tetra-ethylene glycols (polar) at the primary face. The end of each tri- and tetra-ethylene glycol chain is further modified with different terminal functionalities in term of their dipole moment (O-methyl vs O-acetyl vs O-2-cyanoethyl). This has generated several subgroups of amphiphilic β-cyclodextrin derivatives with a systematic change of their relative volumes of the hydrophobic and hydrophilic regions. Our studies showed that all these derivatives self-assemble into thermotropic liquid crystals, with the majority forming hexagonal column mesophases while three compounds form a bicontinuous cubic phase. We rationalized the mesomorphic behaviour of these compounds in term of the relative total van der Waals fractional volumes occupied by the hydrophilic and hydrophobic chains. Upon added with LiTFSI, the formed bicontinuous cubic phase (as a pure compound) was found to transition to form the more stable smectic A mesophase (composite), and both solid NMR studies and impedance spectroscopy revealed that these novel amphiphilic β-cyclodextrin-based liquid crystalline materials have the potential to be used as efficient electrolytes for lithium conduction.

Database of Nonaqueous Proton-Conducting Materials

This work presents the assembly of 48 papers, representing 74 different compounds and blends, into a machine-readable database of nonaqueous proton-conducting materials. SMILES was used to encode the chemical structures of the molecules, and we tabulated the reported proton conductivity, proton diffusion coefficient, and material composition for a total of 3152 data points. The data spans a broad range of temperatures ranging from -70 to 260 °C. To explore this landscape of nonaqueous proton conductors, DFT was used to calculate the proton affinity of 18 unique proton carriers. The results were then compared to the activation energy derived from fitting experimental data to the Arrhenius equation. It was found that while the widely recognized positive correlation between the activation energy and proton affinity may hold among closely related molecules, this correlation does not necessarily apply across a broader range of molecules. This work serves as an example of the potential analyses that can be conducted using literature data combined with emerging research tools in computation and data science to address specific materials design problems.

Anhydrous Proton Transport within Phosphonic Acid Layers in Monodisperse Telechelic Polyethylenes

Polymers bearing phosphonic acid groups have been proposed as anhydrous proton-conducting membranes at elevated operating temperatures for applications in fuel cells. However, the synthesis of phosphonated polymers and the control over the nanostructure of such polymers is challenging. Here, we report the straightforward synthesis of phosphonic acid-terminated, long-chain aliphatic materials with precisely 26 and 48 carbon atoms (C₂₆PA₂ and C₄₈PA₂). These materials combine the structuring ability of monodisperse polyethylenes with the ability of phosphonic acid groups to form strong hydrogen-bonding networks. Anhydride formation is absent so that charge carrier loss by a condensation reaction is avoided even at elevated temperatures. Below the melting temperature (T_m), both materials exhibit a crystalline polyethylene backbone and a layered morphology with planar phosphonic acid aggregates separated by 29 and 55 Å for C₂₆PA₂ and C₄₈PA₂, respectively. Above T_m, the amorphous polyethylene (PE) segments coexist with the layered aggregates. This phenomenon is especially pronounced for the C₂₆PA₂ and is identified as a thermotropic smectic liquid crystalline phase. Under these conditions, an extraordinarily high correlation length (940 Å) along the layer normal is observed, demonstrating the strength of the hydrogen bond network formed by the phosphonic acid groups. The proton conductivity in both materials in the absence of water reaches 10^-4 S/cm at 150 °C. These new precise phosphonic acid-based materials illustrate the importance of controlling the chemistry to form self-assembled nanoscale aggregates that facilitate rapid proton conductivity.