Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal

Transition Mechanism from the Metastable Two-Dimensional Gel to the Stable Three-Dimensional Crystal of Imidazolium-Based Ionic Liquids

One important quest for making high quality materials with amphiphiles is to understand how a disordered self-assembly changes to a stable crystalline state. Herein, we addressed the basic question by investigating the phase transition mechanism of imidazolium-based ionic liquid (IL) [C16mim]Br, using time-resolved small- and wide-angle X-ray scattering (SAXS-WAXS), differential scanning calorimetry, and Fourier transform infrared spectroscopy techniques. Totally, a hexagonal phase, two lamellar-gel phases, and three lamellar-crystalline phases were observed, showing the special polymorphism of the system. It was demonstrated that at low concentrations the two-dimensional gel phase (Lβ1) transforms into the most stable lamellar-crystal phase (Lc3) through two intermediate crystalline phases Lc1 and Lc2. At high concentrations, the Lβ1 phase changes to a condensed lamellar gel phase (Lβ2) before changing to Lc2 and eventually to Lc3. Comparative studies using [C16mim]Cl and [C16mim]NO3 unveiled that the interactions between the counterions and the headgroups of the IL, as well as the dehydration process, govern the nucleation process of Lc3 and thus the formation of the crystal. The in-depth investigation on the transition mechanism and the phase polymorphism in the present work advances our understanding of the crystallization of amphiphilic ionic liquids in dispersions and would promote future applications.

Free-Standing Two-Dimensional Crystals Formed from Self-Assembled Ionic Liquids

The fabrication of two-dimensional crystals (2DCs) has attracted very large interest because it creates materials with various surface structural features and special surface properties. Normally, this is limited to sheets networked together with strong covalent or coordination bonds. Against this understanding, we discovered macroscopic scale free-standing 2DCs in the aqueous dispersions of [C_nmim]X (X = Br, NO₃; n = 14, 16, 18) using simultaneous synchrotron small- and wide-angle X-ray scattering techniques. On the other hand, the 2DCs are also a kind of novel hydrogel holding water content up to 98 wt %. This unusual phenomenon is attributed to the weak interactions between imidazole headgroups and counterions. The observation reported in this work is expected to contribute to theorists in their pursuit of the general principles governing the stability of 2D materials. It may also enlighten experimentalists in designing new free-standing 2DCs for various applications.

Ionic liquid-assisted synthesis of mesoporous polymers and carbon materials: the self-assembly mechanism

Soft-templating synthesis has been widely employed to fabricate ordered mesoporous polymer and carbon materials with effectively tuneable pore sizes. However, the commonly used templating agents, block copolymers, are normally decomposed during the process, thus are barely recyclable; this increases the costs and hampers the scale-up feasibility. Therefore, it becomes imperative to seek promising alternatives; amphiphilic ionic liquids (ILs) are excellent candidates due to their good recyclability. This study explored the templating behaviour of IL templates for preparing mesoporous polymers and carbons. In details, the self-assembly of ternary systems (comprising of IL templates, precursors and solvent) were investigated by a combination of coarse-grained molecular dynamics (CGMD) simulations, density function theory (DFT) calculations and experimental techniques. The results indicate that the morphologies of IL templates are tuneable not only by the adjustment of water content in the mixture but also by the selection of suitable precursors. Material precursors containing increasing numbers of hydroxyl moieties also induce various precursor-template spatial correlations, resulting in different topological structures of nanomaterials. This work presents a fundamental investigation into the mechanisms of templating synthesis with amphiphilic ILs as recyclable templates and gives insight into the effective design of coveted carbon nanomaterials for targeted applications.

In situ biomimetic lyotropic liquid crystal gel for full-thickness cartilage defect regeneration

There is a great challenge in regenerating cartilage defects, which usually involve absent bearing capacity and poor adaptation to joint movement, further exacerbating subchondral bone damage. Therefore, ideal tissue-engineering cartilage scaffolds should be endowed with biomimetic and sustained-release function for promoting long-term chondrogenesis while protecting subchondral bone. Herein, in situ self-assembling gel based on glyceryl monooleate (GMO)-hyaluronic acid (HA) composite lyotropic liquid crystal (HLC) was developed as the biomimetic scaffold to deliver kartogenin for long-term cartilage regeneration. Compared to the GMO based (LLC) gel, HLC gel with modified lattice structure exhibited improved rheological properties for better joint protection by increasing mechanical strength, elasticity and lubrication. Besides, HLC gel successfully prolonged drug release and retention in the joint cavity over 4 weeks to provide combined effect of kartogenin and HA for cartilage repair. Pharmacodynamic studies demonstrated that HLC gel was the most effective to promote chondrogenesis and protect subchondral bone, making the damaged bone tissue restored to normal in divergent features as evidenced by the MRI, Micro-CT and histological results. Therefore, the HLC gel with joint protection and controlled drug release can serve as a firm scaffold for providing long-term cartilage repair.

Improved ordering and lubricating properties using graphene in lamellar liquid crystals of Triton X-100/CnmimNTf2/H2O

Graphene has been studied extensively owing to its excellent lubricity performance. However, when used as lubricant additives, graphene layers tend to agglomerate and precipitate; further, poor dispersion will reduce the lubrication performance. Herein, graphene was evenly dispersed in Triton X-100/1-alkyl-3-methylimidazole ditrifluorosulfonylimide (CnmimNTf2)/H2O (n = 8, 12, and 16) lamellar liquid crystals (LLCs). The effects of the graphene concentration on the microstructures of the LLCs are detected by 2H NMR and small angle X-ray scattering measurements and their rheological and tribological performance are investigated in detail. The addition of 0.30 mg mL-1 graphene into the Triton X-100/C16mimNTf2/H2O LLC system led to a 15% reduction in the friction coefficient and 65% reduction in the wear volume when compared with the pure LLCs. The synergistic effect of the graphene and LLC hybrid system efficiently improved the lubrication performance, which is attributed to the higher order of the amphiphilic molecules and the thicker amphiphilic bilayer. The generated tribofilm formed by the physical adsorption and the tribochemical reaction of LLCs on the surface of steel is conducive to lubricity protection from abrasion. This study reveals that with the understanding of the microstructure change mechanism, the combination of graphene and LLCs could provide a new path to the design of a novel lubricant that can be utilized in nanostructures for energy saving applications.

Liquid crystal delivery of ciprofloxacin to treat infections of the female reproductive tract

Infections of the female reproductive tract are a major cause of morbidity and mortality in humans, requiring significant investment to sustain treatment and representing a major challenge to health. The increasing prevalence of bacterial resistance, and an almost complete absence of new antibiotic therapies for the past five decades, mean there is a desperate need for novel approaches to the treatment of bacterial infections. Within the present study, we demonstrate the effective ex vivo treatment of bacterial infection of the female reproductive tract using a controlled-release, liquid crystal-based platform. Liquid crystal encapsulation of ciprofloxacin significantly enhanced its bactericidal efficacy and reduced cell toxicity. Liquid crystal structures are low-cost, simple to manufacture and provide a sustained-release profile of encapsulated ciprofloxacin. Treatment of Escherichia coli infected reproductive tract epithelial cells and whole organ cultures with liquid crystal encapsulated ciprofloxacin proved to be an effective strategy for reducing bacterial load and reproductive tract inflammatory responses to infection. These data suggest that such an approach could provide an efficacious treatment modality for enhancing the effectiveness of current antibiotic therapies.

Microstructure and Tribological Properties of Lamellar Liquid Crystals Formed by Ionic Liquids as Cosurfactants

Lamellar liquid crystals (LLCs) have been shown to have lubrication properties in many documents due to their bilayer structure. Ionic liquids are often used as additive or surfactant in LLCs. However, ionic liquids used as cosurfactants, which lead to a transition from the hexagonal liquid crystals to LLCs, are relatively rare. Herein, the microstructure of Triton X-100/C _nmimNTf₂/H₂O LLCs formed by using 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (C _nmimNTf₂, n = 8, 12, 16) as cosurfactant has been determined by polarized light microscopy, small angle X-ray scattering, and ²H NMR technique, and their rheological and tribological properties were investigated. These LLCs show good friction-reducing and antiwear performances. The correlation between the microstructure of the LLCs and their lubricating mechanism is established. The increase of the concentration of C _nmimNTf₂ and the length of alkyl chain in the LLCs can lead to an obvious reduction in friction coefficients and wear volumes, which are attributed to the higher order of amphiphilic molecules, the thickness of the amphiphilic bilayer, and the smaller cross-sectional area of the polar head group at the hydrophilic and hydrophobic interfaces. The protective film formed by the physical adsorption of ionic liquid LLCs on the surface of friction disk pair and the tribochemical reaction has effectively promoted the lubrication effect. The good lubricating property and antiwear capability indicate their promising and potential applications in water lubrication and biological lubrication.

Graphene based room temperature flexible nanocomposites from permanently cross-linked networks

Graphene based room temperature flexible nanocomposites were prepared using epoxy thermosets for the first time. Flexible behavior was induced into the epoxy thermosets by introducing charge transfer complexes between functional groups within cross linked epoxy and room temperature ionic liquid ions. The graphene nanoplatelets were found to be highly dispersed in the epoxy matrix due to ionic liquid cation–π interactions. It was observed that incorporation of small amounts of graphene into the epoxy matrix significantly enhanced the mechanical properties of the epoxy. In particular, a 0.6 wt% addition increased the tensile strength and Young’s modulus by 125% and 21% respectively. The electrical resistance of nanocomposites was found to be increased with graphene loading indicating the level of self-organization between the ILs and the graphene sheets in the matrix of the composite. The graphene nanocomposites were flexible and behave like ductile thermoplastics at room temperature. This study demonstrates the use of ionic liquid as a compatible agent to induce flexibility in inherently brittle thermoset materials and improve the dispersion of graphene to create high performance nanocomposite materials.