Lamellar Lyotropic Liquid Crystal Superior to Micellar Solution for Proton Conduction in an Aqueous Solution of 1-Tetradecyl-3-methylimidazolium Hydrogen Sulfate

Self-assembly of the imidazolium surfactant in aprotic ionic liquids. The anion effect of aprotic ionic liquids

The structure of ionic liquids (ILs) has an influence on their physiochemical properties, determining their performance as self-assembly media. In this study, we focus on the anion effect of aprotic ionic liquids (AILs). The aggregation behaviours of the cationic surfactant 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) have been investigated in the imidazolium AILs with the 1-ethyl-3-methyl imidazolium cation and different anions, including nitrate, ethylsulfate, bis(trifluoromethylsulfonyl) imide and tetrafluoroborate. Surface adsorption parameters of C16mimBr were determined using surface tension measurements, and the critical micellization concentration values in AILs vary for their different cohesive energy. The micellar and lamellar lyotropic liquid crystal phases emerge with the increase of C16mimBr concentrations. The structure and properties of aggregates were determined using small angle X-ray scattering, polarized optical microscopy, rheology and differential scanning calorimetry. The anion effects of AILs on the phase behaviours and structure and properties of aggregates were analysed and discussed. The lamellar lyotropic liquid crystals have shown good conductivity, as confirmed by electrochemical impedance spectroscopy characterization. Our results enhance the understanding of the structure effect of ILs as self-assembly media and contribute to the design of tailorable solvents.

Lyotropic Lamellar Nanostructures Enabled High-Voltage Windows, Efficient Charge Transport, and Thermally Safe Solid-State Electrolytes for Lithium-Ion Batteries

Developing electrolytes combining solid-like instinct stability and liquid-like conducting performance will be satisfactory for efficient and durable Li-ion batteries. Herein lamellar lyotropic liquid crystals (LLCs) demonstrate high-voltage windows, efficient charge transport, and inherent thermal safety as solid-state electrolytes in lithium-ion batteries. Lamellar LLCs are simply prepared by nanosegregation of [C16Mim][BF4] and LiBF4/Propylene carbonate (PC) liquid solutions, which induce lamellar assembly of the liquids as dynamic conducting pathways. Broadened liquid conducting pathways will boost the conducting performance of the LLC electrolytes. The lyotropic lamellar nanostructures enable liquid-like ion conductivity of the LLC electrolytes at ambient temperatures, as well as provide solid-like stability for the electrolytes to resist high voltage and flammability overwhelming to LiBF4/PC liquid electrolytes. Despite minor consumption of PC solvents (34.5 wt.%), the lamellar electrolytes show energy conversion efficiency comparable to the liquid electrolytes (PC wt. 92.8%) in Li/LiFePO4 batteries under ambient temperatures even at a 2 C current density, and exhibit attractively robust stability after 200th cyclic charge/discharge even under 60 °C. The work demonstrates LLC electrolytes have great potential to supersede traditional liquid electrolytes for efficient and durable Lithium-ion (Li-ion) batteries.

Effect of polyacrylamide morphology templated using lyotropic liquid crystal on the proton conductivity of acid hydrogels

Acid hydrogels comprising polymer networks are promising soft electrolytes whose proton conductivities are most often regulated by acid content. Herein, promotion of conductivity by solely regulating polymer morphology has been demonstrated for acid hydrogels with identical acid content. Polymerization of acrylamide at different temperatures in the same aqueous solution, which is a lyotropic liquid crystal (LLC) of 4-(1-ethyldecyl)benzenesulfonic acid (EDBSA) exhibiting a phase transition at 30 °C, affords acid hydrogels comprising ordered and random polymer networks. The ordered polymer network templated by the lamellar liquid crystal at 15 °C possesses more interconnected and extended pores than that obtained in the isotropic solution at 45 °C. Electrochemical characterization shows that the ordered network affords 48% higher proton conductivity than the random network for hydrogels holding the EDBSA LLC. This higher conductivity is ascribed to more numerous long-range transport pathways formed in larger pores and fewer barriers in the network for protons to pass through. Enhanced conductivities are also obtained from the ordered polymer network for hydrogels comprising micellar EDBSA solution and H₂SO₄ solution, albeit to lesser degrees. These results shed light on the dependence of electrochemical performance on the polymer morphology of hydrogels and offer a strategy to enhance the conductivity of hydrogels without changing their polymer fraction.

Advanced Functional Liquid Crystals

Liquid crystals have been intensively studied as functional materials. Recently, integration of various disciplines has led to new directions in the design of functional liquid-crystalline materials in the fields of energy, water, photonics, actuation, sensing, and biotechnology. Here, recent advances in functional liquid crystals based on polymers, supramolecular complexes, gels, colloids, and inorganic-based hybrids are reviewed, from design strategies to functionalization of these materials and interfaces. New insights into liquid crystals provided by significant progress in advanced measurements and computational simulations, which enhance new design and functionalization of liquid-crystalline materials, are also discussed.