Synthesis and Characterization of Polymerized Ionic Liquids: Mechanical and Thermal Properties of a Novel Type of Hydrogels

An All-Solid-State Flexible Supercapacitor Based on MXene/MSA Ionogel and Polyaniline Electrode with Wide Temperature Range, High Stability, and High Energy Density

In this study, an ionogel electrolyte (PAIM-X) consisting of 1-vinyl-3-methylimidazole bis (trifluoromethyl sulfonyl) imide ([VMIM][TFSI]), Polyacrylamide (PAAm), and MXene were prepared. The conductivity of PAIM-X and integral area of the voltammetric curve of the supercapacitor (PAIMSC) were improved by adding MXene. The addition of [VMIM][TFSI] enhanced the conductivity and applicable temperature of the ionogel electrolyte. At 90 °C, the conductivity of PAIM-4 can reach 36.4 mS/cm. In addition, spherical polyaniline with good electrochemical properties was synthesized and coated on graphite paper as an active substance. An all-solid-state supercapacitor was composed of PAIM-4, polyaniline electrode with 1.2 V potential window, pseudo-capacitors and high quality capacitors. The solvent 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulfonyl imide) ([EMIM][TFSI]) and methanesulfonic acid (MSA) were introduced into the ionogel to promote the redox reaction of polyaniline (PANI). The mass specific capacitance of PAIMSC was 204.6 F/g and its energy density could reach 40.92 Wh/kg, which shows great potential for practical application at high temperature. The device had good rate performance and cycle performance, and its capacitance retention rate was still 91.56% after 10,000 cycles. In addition, the supercapacitor can work within the temperature range of -20 °C to 90 °C. These excellent electrochemical properties indicate that PAAm/IL/Mxene-X has broad application space and prospect.

Fast Gelation of Poly(ionic liquid)-Based Injectable Antibacterial Hydrogels

Traditional antibacterial hydrogels have a broad-spectrum bactericidal effect and are widely used as wound dressings. However, the biological toxicity and drug resistance of these antibacterial hydrogels cannot meet the requirements of long-term clinical application. Imidazolium poly(ionic liquids) (PILs) are polymeric antibacterial agents exhibiting strong antibacterial properties, as they contain a strong positive charge. In this study, two imidazolium PILs, namely poly(N-butylimidazolium propiolic acid sodium) (PBP) and poly(N-(3,6-dioxaoctane) imidazolium propiolic acid sodium) (PDP), as high efficiency antibacterial agents, were synthesized by polycondensation reaction. Then, the PILs were compounded with polyethylene glycol (PEG) by a thiol-yne click reaction to prepare injectable antibacterial hydrogels. An in vitro assay showed that the injectable antibacterial hydrogels could not only quickly kill Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), but also had low toxicity for human skin fibroblasts cells (HSFs) and human umbilical vein endothelial cells (HUVECs), respectively. Additionally, the lipopolysaccharide (LPS) inflammation model revealed that the injectable antibacterial hydrogels also had anti-inflammatory effects, which would be advantageous to accelerate wound healing.

Swelling and Diffusion in Polymerized Ionic Liquids-Based Hydrogels

Hydrogels are one of the emerging classes of materials in current research. Besides their numerous applications in the medical sector as a drug delivery system or in tissue replacement, they are also suitable as irrigation components or as immobilization matrices in catalysis. For optimal application of these compounds, knowledge of the swelling properties and the diffusion mechanisms occurring in the gels is mandatory. This study is focused on hydrogels synthesized by radical polymerization of imidazolium-based ionic liquids. Both the swelling and diffusion behavior of these hydrogels were investigated via gravimetric swelling as well as sorption experiments implemented in water, ethanol, n-heptane, and tetrahydrofuran. In water and ethanol, strong swelling was observed while the transport mechanism deviated from Fickian-type behavior. By varying the counterion and the chain length of the cation, their influences on the processes were observed. The calculation of the diffusion coefficients delivered values in the range of 10⁻¹⁰ to 10⁻¹² m² s⁻¹. The gravimetric results were supported by apparent diffusion coefficients measured through diffusion-weighted magnetic resonance imaging. A visualization of the water diffusion front within the hydrogel should help to further elucidate the diffusion processes in the imidazolium-based hydrogels.

Semi-interpenetrating chitosan/ionic liquid polymer networks as electro-responsive biomaterials for potential wound dressings and iontophoretic applications

In this work, electro-responsive chitosan/ionic liquid-based hydrogels were synthetized for the first time, envisaging the development of iontophoretic biomaterials for the controlled release/permeation of charged biomolecules. The main goal was to enhance and tune the physicochemical, mechanical, electro-responsive, and haemostatic properties of chitosan-based biomaterials to obtain multi-stimuli responsive (responsive to electrical current, ionic strength, and pH) and mechanically stable hydrogels. To accomplish this objective, polycationic semi-interpenetrating copolymer networks (semi-IPN) were prepared by combining chitosan (CS) and ionic liquid-based polymers and copolymers, namely poly(1-butyl-3-vinylimidazolium chloride) (poly(BVImCl)) and poly(2-hydroxymethyl methacrylate-co-1-butyl-3-vinylimidazolium chloride) (poly(HEMA-co-BVImCl)). Results show that prepared semi-IPNs presented high mechanical stability and were positively charged over a broad pH range, including basic pH. Semi-IPNs also presented faster permeation and release rates of lidocaine hydrochloride (LH), under external electrical stimulus (0.56 mA/cm²) in aqueous media at 32 °C. The kinetic release constants and the LH diffusion coefficients measured under electrical stimulus were ~1.5 and > 2.7 times higher for those measured for passive release. Finally, both semi-IPNs were non-haemolytic (haemolytic index ≤0.2%) and showed strong haemostatic activity (blood clotting index of ~12 ± 1%). Altogether, these results show that the prepared polycationic semi-IPN hydrogels presented advantageous mechanical, responsive and biological properties that enable them to be potentially employed for the design of new, safer, and advanced stimuli-responsive biomaterials for several biomedical applications such as haemostatic and wound healing dressings and iontophoretic patches.

Role of Fast Dynamics in Conductivity of Polymerized Ionic Liquids

Polymerized ionic liquids (PolyILs) are promising candidates for a broad range of technologies. However, the relatively low conductivity of PolyILs at room temperature has strongly limited their applications. In this work, we provide new insights into the roles of various microscopic parameters controlling ion transport in these polymers, which are crucial for their rational design and practical applications. Using broadband dielectric spectroscopy and neutron and light scattering techniques, we found a clear connection between the activation energy for conductivity, fast dynamics, and high-frequency shear modulus in PolyILs at their glass transition temperature (T_g). In particular, our analysis reveals a correlation between conductivity and the amplitude of fast picosecond fluctuations at T_g, suggesting the possible involvement of fast dynamics in lowering the energy barrier for ion conductivity. We also demonstrate that both the activation energy for ion transport and the amplitude of the fast fluctuations depend on the high-frequency shear moduli of PolyILs, thus identifying a practically important parameter for tuning conductivity. The parameters recognized in this work and their connection to the ionic conductivity of PolyILs set the stage for a deeper understanding of the mechanism of ion transport in PolyILs in the glassy state.

UV-Polymerized Vinylimidazolium Ionic Liquids for Permselective Membranes

Ionic liquids are highly charged compounds with increasing applications in material science. A universal approach to synthesize free-standing, vinylalkylimidazolium bromide-containing membranes with an adjustable thickness is presented. By the variation of alkyl side chains, membrane characteristics such as flux and mechanical properties can be adjusted. The simultaneous use of different ionic liquids (ILs) in the synthesis can also improve the membrane properties. In separation application, these charged materials allowed us to retain charged sugars, such as calcium gluconate, by up to 95%, while similar neutral compounds such as glucose passed the membrane. An analysis of the surface conditions using atomic force microscopy (AFM) confirmed the experimental data and explains the decreasing permeance and increased retention of the charged sugars.

Swelling characteristics and biocompatibility of ionic liquid based hydrogels for biomedical applications

Polymers are commonly used in medical device manufacturing, e.g. for drug delivery systems, bone substitutes and stent coatings. Especially hydrogels exhibit very promising properties in this field. Hence, the development of new hydrogel systems for customized application is of great interest, especially regarding the swelling behavior and mechanical properties as well as the biocompatibility. The aim of this work was the preparation and investigation of various polyelectrolyte and poly-ionic liquid based hydrogels accessible by radical polymerization. The obtained polymers were covalently crosslinked with N,N'-methylenebisacrylamide (MBAA) or different lengths of poly(ethyleneglycol)diacrylate (PEGDA). The effect of different crosslinker-to-monomer ratios has been examined. In addition to the compression curves and the maximum degree of swelling, the biocompatibility with L929 mouse fibroblasts of these materials was determined in direct cell seeding experiments and the outcome for the different hydrogels was compared.

Characterization and application of chemical-resistant polyurethane-based enzyme and whole cell compartments

This study presents the preparation and physical-chemical characterization of chemical resistant polyurethane-based compartments for biocatalytic application. The artificial compartments were prepared from an emulsion of polymer precursor and an aqueous phase that includes a biocatalytic reaction system. After curing, highly dispersed aqueous domains were obtained, which still contain the entire biocatalytic reaction system and remain fixed in the solid polymer preparation. The tensile and compression behavior of the prepared polymeric material is not significantly affected by the incorporation and facilitates excellent stability against various organic solvents and acid solutions. Thereby, the compartments can be used not only for enantioselective alcohol-dehydrogenase catalyzed reduction but also for a whole cell catalyzed hydrolysis of esters. Moreover, the compartmented whole-cell system was considerably stable to allow multiple reuses without a noticeable loss of catalytic activity of the incorporated whole cell catalytic reaction system.

Structural correlations tailor conductive properties in polymerized ionic liquids

In this paper, it was demonstrated that the mobile ion (anion) size and pendant group chemistry affect the packing of the polymer chains and influence conductivity in imidazolium based PolyILs.

Polymerized Ionic Liquids: Correlation of Ionic Conductivity with Nanoscale Morphology and Counterion Volume

The impact of the chemical structure on ion transport, nanoscale morphology, and dynamics in polymerized imidazolium-based ionic liquids is investigated by broadband dielectric spectroscopy and X-ray scattering, complemented with atomistic molecular dynamics simulations. Anion volume is found to correlate strongly with T_g-independent ionic conductivities spanning more than 3 orders of magnitude. In addition, a systematic increase in alkyl side chain length results in about one decade decrease in T_g-independent ionic conductivity correlating with an increase in the characteristic backbone-to-backbone distances found from scattering and simulations. The quantitative comparison between ion sizes, morphology, and ionic conductivity underscores the need for polymerized ionic liquids with small counterions and short alkyl side chain length in order to obtain polymer electrolytes with higher ionic conductivity.

Ultrastretchable Iono-Elastomers with Mechanoelectrical Response

The emerging technologies involving wearable electronics require new materials with high stretchability, resistance to high loads, and high conductivities. We report a facile synthetic strategy based on self-assembly of concentrated solutions of end-functionalized PEO₁₀₆-PPO₇₀-PEO₁₀₆ triblock copolymer in ethylammonium nitrate into face-centered cubic micellar crystals, followed by micelle corona cross-linking to generate elastomeric ion gels (iono-elastomers). These materials exhibit an unprecedented combination of high stretchability, high ionic conductivity, and mechanoelectrical response. The latter consists of a remarkable and counterintuitive increase in ion conductivity with strain during uniaxial extension, which is reversible upon load release. Based on in situ SAXS measurements of reversible crystal structure transformations during deformation, we postulate that the origin of the conductivity increase is a reversible formation of ion nanochannels due to a novel microstructural rearrangement specific to this material.

Probing Nanoscale Ion Dynamics in Ultrathin Films of Polymerized Ionic Liquids by Broadband Dielectric Spectroscopy

Continuous progress in energy storage and conversion technologies necessitates novel experimental approaches that can provide fundamental insights regarding the impact of reduced dimensions on the functional properties of materials. Here, we demonstrate a nondestructive experimental approach to probe nanoscale ion dynamics in ultrathin films of polymerized 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide over a broad frequency range spanning over 6 orders of magnitude by broadband dielectric spectroscopy. The approach involves using an electrode configuration with lithographically patterned silica nanostructures, which allow for an air gap between the confined ion conductor and one of the electrodes. We observe that the characteristic rate of ion dynamics significantly slows down with decreasing film thicknesses above the calorimetric glass transition of the bulk polymer. However, the mean rates remain bulk-like at lower temperatures. These results highlight the increasing influence of the polymer/substrate interactions with decreasing film thickness on ion dynamics.

Preparation of Poly(ionic liquid)s-Supported Recyclable Organocatalysts for the Asymmetric Nitroaldol (Henry) Reaction

A novel strategy for the embedding of quinine-based organocatalysts in polymerized ionic liquids-based hydrogels is presented. With this technique, the encapsulated organocatalyst was successfully recovered and reused for four cycles without any loss of enantioselectivity (up to 91% ee) for the asymmetric nitroaldol (Henry) reaction. In this study, high catalyst leaching was significantly reduced (<0.01%) by controlling the water content. After catalyst removal, evaporation of the solvent affords the product in 98% purity without any further purification.

Tuning the Pore Size in Gradient Poly(ionic liquid) Membranes by Small Organic Acids

Highly charged porous polymer membranes with adjustable pore size and gradient pore structure along the membrane cross-section were prepared by ammonia-triggered electrostatic complexation between an imidazolium-based cationic poly(ionic liquid) (PIL) and multivalent benzoic acid derivatives. The PIL and the acid compound were first dissolved homogeneously in DMSO, cast into a thin film onto a glass plate, dried, and finally immersed into an aqueous ammonia solution. The diffusion of ammonia from the top to the bottom into the film neutralized the acid and introduced the gradient pore structure and in situ electrostatic cross-linking to fix the pores. The pore size and its distribution of the membranes were found controllable in terms of the multivalency of the acids, the imidazolium/carboxylate ratio, and the nature of the PIL counteranion.

Usage of different vessel models in a flow-through cell: in vitro study of a novel coated balloon catheter

Calcium alginate and polyacrylamide hydrogels were used as tissue models for the simulated anatomic implantation process.