Supramolecular ionic liquid gels for quasi-solid-state dye-sensitized solar cells

Green, pH-Sensitive, Highly Stretchable, and Hydrogen Bond-Dominated Ionogel for Wound Healing Activity

Traditional hydrogel dressings generally have poor mechanical properties and stability when subjected to external stress due to the undesirable chain entanglement structure of their single valence bond compositions. Therefore, it is particularly important to develop a type of gel dressing with good mechanical strength, stability, and environment-friendly monitoring. In this work, a transparent, pH-sensitive, highly stretchable, and biocompatible anthocyanidin ionogel dressing was prepared, realizing green and accurate detection. Attributed to the antibacterial activity of the ionic liquid, the biocompatibility of the pectin, and the ability to scavenge free radicals of the anthocyanidin, the ionogel dressing exhibited excellent re-epithelialization in the 14 day wound healing process. Besides, changes in pH values monitoring of the ionogel over 3 days coincided with normal wound exudate. The obtained ionogel also showed good water retention, swelling properties, mechanical stretchability, and 5 week stability, illustrating great potential in wound dressings.

Capacitance Effects of a Hydrophobic-Coated Ion Gel Dielectric on AC Electrowetting

We present experimental studies of alternating current (AC) electrowetting dominantly influenced by several unique characteristics of an ion gel dielectric in its capacitance. At a high-frequency region above 1 kHz, the droplet undergoes the contact angle modification. Due to its high-capacitance characteristic, the ion gel allows the contact angle change as large as Δθ = 26.4°, more than 2-fold improvement, compared to conventional dielectrics when f = 1 kHz. At the frequency range from 1 to 15 kHz, the capacitive response of the gel layer dominates and results in a nominal variation in the angle change as θ ≈ 90.9°. Above 15 kHz, such a capacitive response of the gel layer sharply decreases and leads to the drastic increase in the contact angle. At a low-frequency region below a few hundred Hz, the droplet’s oscillation relying on the AC frequency applied was mainly observed and oscillation performance was maximized at corresponding resonance frequencies. With the high-capacitance feature, the ion gel significantly enlarges the oscillation performance by 73.8% at the 1st resonance mode. The study herein on the ion gel dielectric will help for various AC electrowetting applications with the benefits of mixing enhancement, large contact angle modification, and frequency-independent control.

Supramolecular self-healing materials from non-covalent cross-linking host-guest interactions

The introduction of non-covalent bonds is effective for achieving self-healing properties because they can be controlled reversibly. One approach to introduce these bonds into supramolecular materials is use of host-guest interactions. This feature article summarizes the development of supramolecular materials constructed by non-covalent cross-linking through several approaches, such as host-guest interactions between host polymers and guest polymers, 1 : 2-type host-guest interactions, and host-guest interactions from the polymerization of host-guest inclusion complexes. Host-guest interactions show self-healing functions while also enabling stimuli-responsiveness (redox, pH, and temperature). The self-healing function of supramolecular materials is achieved by stress dispersion arising from host-guest interactions when stress is applied. Reversible bonds based on host-guest interactions have tremendous potential to expand the variety of functional materials.

Poly(ionic liquid) Electrolytes for a Switchable Silver Mirror

Imidazolium-type small-molecule ionic liquids (ILs) and their corresponding poly(ionic liquid) (PIL) homopolymers were synthesized and applied to reversible electrochemical mirrors (REMs). The effects of alkyl chain length of the carbon chains at the N3 position and cation charge density (mono- and bis-imidazolium) on the electrochromic properties of Ag-based REMs were investigated by analyzing their electrodeposition and spectral properties. Longer alkyl chains and higher charge densities decreased the size and resulted in a more uniform distribution of Ag nanoparticles. Compared with IL-based liquid electrolytes, the PIL-based gel electrolytes formed smaller and denser electrodeposited metallic Ag nanoparticles because of their higher viscosity. These findings were used to guide fabrication of a 50 cm² mirror dynamic window and flexible display. Because of several unique properties of PILs, the PIL-based REM exhibits fast switching speeds, superb cycling durability, small particle sizes, and uniform electrodeposited Ag nanoparticle films. These results make dynamic windows based on PIL electrolytes promising and competitive alternatives to traditional electrochromic windows.

Maize-like ionic liquid@polyaniline nanocomposites for high performance supercapacitor

In this study, ionic liquids (IL) containing carboxyl and different alkyl chains were fabricated and used to dope polyaniline (PANI). The results revealed that IL@PANI composites could be facilely obtained via template-free polymerization of aniline using ammonium persulfate as the oxidant. The as-prepared IL@PANI composites were measured by FT-IR, XPS, and SEM. Electrochemical performances of IL@PANI nanocomposites were investigated by cyclic voltammetry and galvanostatic charge/discharge. The results indicate that the alkyl chains of ILs have an important influence on the morphology and capacitance performance of IL@PANI electrode materials. With the shorter alkyl group in ILs, IL@PANI materials presented higher specific capacitance. Especially, 1-vinyl-3-carboxymethyl-imidazolium chloride ([VCMIm]Cl)@PANI composite presented the highest specific capacitance. Cycling performance measurement demonstrated that 82% capacitance retention could be achieved after 1000 cycles in 0.5 M H2SO4 aqueous solution. Therefore, our strategy provides a new technique for PANI nanocomposites with tunable morphology and high performance.

Effect of β-Cyclodextrin on Physicochemical Properties of an Ionic Liquid Electrolyte Composed of N-Methyl-N-Propylpyrrolidinium bis(trifluoromethylsulfonyl)amide

Ionic liquids (ILs) are promising electrolyte materials for developing next-generation rechargeable batteries. In order to improve their properties, several kinds of additives have been investigated. In this study, β-cyclodextrin (β-CD) was chosen as a new additive in IL electrolytes because it can form an inclusion complex with bis(trifluoromethylsulfonyl)amide (TFSA) anions. We prepared the composites by mixing N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)amide/LiTFSA and a given amount of triacetyl-β-cyclodextrin (Acβ-CD). The thermal behaviors and electrochemical properties of the composites were analyzed by several techniques. In addition, pulse field gradient NMR measurements were conducted to determine the self-diffusion coefficients of the component ions. The addition of Acβ-CD to the IL electrolytes results in the decrease in the conductivity value and the increase in the viscosity value. In contrast, the addition of Acβ-CD to the IL electrolytes induced an improvement in the anodic stability because of the formation of an inclusion complex between the Acβ-CD and TFSA anions. CDs are potential candidates as additives in IL electrolytes for electrochemical applications.

Ultrasensitive Interfacial Capacitive Pressure Sensor Based on a Randomly Distributed Microstructured Iontronic Film for Wearable Applications

The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (<2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride- co-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the solid electrolyte help the material to elastically deform under pressure. Moreover, the interfacial capacitance is improved by utilizing a highly conductive porous percolated network of silver nanowires reinforced with poly(dimethylsiloxane) as the electrodes. An ultrahigh-pressure sensitivity of 131.5 kPa^-1, a low dynamic response time of ∼43 ms, a low limit of detection of 1.12 Pa, and a high stability for over 7000 cycles are achieved. Finally, we demonstrate the application of the sensor for international Morse code detection, artery pulse detection, and eye blinking. Owing to the ultrahigh sensitivity, the as-fabricated sensor will have great potential for wearable devices in health status monitoring, motion detection, and electronic skin.

Mechanical and self-recovery properties of supramolecular ionic liquid elastomers based on host–guest interactions and correlation with ionic liquid content

Supramolecular materials have received considerable attention due to their higher fracture energy and self-recovery capability compared to conventional chemically cross-linked materials. Herein, we focus on the mechanical properties and self-recovery behaviours of supramolecular polymeric elastomers swollen with ionic liquid. We also gained insight into the correlation between ionic liquid content and mechanical properties. These supramolecular polymers with ionic liquid can be easily prepared from bulk copolymerization of the host–guest complex (peracetylated cyclodextrin and adamantane derivatives) and alkyl acrylates and subsequent immersion in ionic liquid such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The supramolecular polymeric elastomers showed a self-recovery ability, which the conventional chemically cross-linked elastomers with ionic liquid cannot achieve.

Supramolecular ionic liquid elastomers showed higher fracture energy than chemically cross-linked ionic liquid elastomers and also self-recovery ability.

Smart low molecular weight hydrogels with dynamic covalent skeletons

We report a new strategy for fabricating a smart low molecular weight hydrogel based on dynamic covalent chemistry from a bola-type supra-gelator, which was facilely fabricated in situ from two non-assembling building blocks, (3-(2-(4-formylphenoxy) ethyl)-1-methyl imidazolium bromide, MA) and (3,3'-dithiobis (propionohydrazide), DSPDZ), through dynamic acylhydrazone bonding. The obtained low molecular weight hydrogels exhibited redox-responsive and controllable self-healing properties. The role of dynamic covalent bonding in the formation of smart hydrogels is revealed in this study, which provides a simple and bottom-up method for constructing smart low molecular weight hydrogels.

Low-Molecular-Weight Supramolecular Ionogel Based on Host-Guest Interaction

Supramolecular ionogels were prepared by self-assembly of small molecules through host-guest interaction between β-cyclodextrin (β-CD) and a room-temperature ionic liquid (IL) 3-(1-methyl-3-imidazolio)propanesulfonate-lithium bis(trifluoromethanesulfonyl)imide (MIPS-LiTFSI) which contains zwitterion MIPS. ¹⁹F NMR and 2D ROESY ¹H NMR have been used to prove that only TFSI^- is involved in the complexation. ¹H NMR, FT-IR, and comparative tests indicated that the electrostatic interaction between imidazole cation and TFSI^- anion and intermolecular hydrogen bonding between three compounds also contribute to the formation of supramolecular ionogel. Ionogels with different gel-sol phase transition temperatures can be obtained by adjusting the molar ratio between β-CD and MIPS-LiTFSI. In addition, the supramolecular ionogels composed of "channel type" structural β-CD have been constructed. The ionogel with high conductivity and low activation energy open a door to new fields for special applications.

Plasmon-Induced Broadband Light-Harvesting for Dye-Sensitized Solar Cells Using a Mixture of Gold Nanocrystals

The efficiency of dye-sensitized solar cells (DSSCs) is generally limited by the mismatch between the absorption spectrum of the photosensitizer and the solar irradiation spectrum. This work describes the use of a mixture that containing proper proportions of SiO2 coated Au nanospheres (AuNSs@SiO2 ) and Au nanorods (AuNRs@SiO2 ) (the mixture was denoted as AuNCs@SiO2 ) to enhance the sunlight utility in DSSCs. The incorporation of AuNCs@SiO2 into the TiO2 photoanode induced broadband light-harvesting at both low- and long- wavelengths and thus enhanced the photocurrent compared to that of plasmonic solar cells based on either AuNSs@SiO2 or AuNRs@SiO2 . Upon the doping of AuNCs@SiO2 , the overall power conversion efficiency (PCE) increased from 7.39 to 9.12 % for DSSCs based on organic liquid electrolytes.

Poly(Ionic Liquid) Semi-Interpenetrating Network Multi-Responsive Hydrogels

Herein we describe poly(ionic liquid) hydrogel actuators that are capable of responding to multiple stimuli, namely temperature, ionic strength and white light irradiation. Using two starting materials, a crosslinked poly ionic liquid (PIL) and a linear poly(N-isopropylacrylamide-co-spiropyran-co-acrylic acid), several semi-interpenetrating (sIPN) hydrogels were synthesised. The dimensions of hydrogels discs were measured before and after applying the stimuli, to quantify their response. Samples composed of 100% crosslinked PIL alone showed an average area reduction value of ~53% when the temperature was raised from 20 °C to 70 °C, ~24% when immersed in 1% w/w NaF salt solution and no observable photo-response. In comparison, sIPNs containing 300% w/w linear polymer showed an average area reduction of ~45% when the temperature was raised from 20 °C to 70 °C, ~36% when immersed in 1% NaF w/w salt solution and ~10% after 30 min exposure to white light irradiation, respectively. Moreover, by varying the content of the linear component, fine-control over the photo-, thermo- and salt response, swelling-deswelling rate and mechanical properties of the resulting sIPN was achieved.

Liquid crystal self-assembly of halloysite nanotubes in ionic liquids: a novel soft nanocomposite ionogel electrolyte with high anisotropic ionic conductivity and thermal stability

We report a novel class of liquid crystalline (LC) nanohybrid ionogels fabricated via self-assembly of natural halloysite nanotubes (HNTs) in ionic liquids (ILs). The obtained ionogels are very stable and nonvolatile and show LC phases over a wide temperature range. Remarkably, the nanocomposite ionogels exhibit high anisotropic ionic conductivity after shear, and their room temperature ionic conductivity can reach 3.8 × 10(-3) S cm(-1) for aligned nanotubes perpendicular to the electrode even when the HNTs content increases to 40 wt%, which is 380 times higher than that obtained for aligned nanotubes parallel to the electrode, which is 1.0 × 10(-5) S cm(-1). Crucially, the obtained LC nanocomposite ionogels have very high thermal stability, which can sustain 400 °C thermal treatment. The findings will promote the development of novel nanocomposite ionogel electrolytes with faster ion transport and larger anisotropic conductivity.

Inorganic salt templated porous TiO2 photoelectrode for solid-state dye-sensitized solar cells

Salt template induced TiO₂ photoelectrodes with channels (or pores) were applied to improve the photoelectric conversion efficiency of solid-state dye-sensitized solar cells.

A tough self-assembled natural oligomer hydrogel based on nano-size vesicle cohesion

Vesicles made from shellac-COOH similar to asymmetric gemini surfactants could aggregated together to fabricate the network of the shellac hydrogel.

Facile preparation of supramolecular ionogels exhibiting high temperature durability as solid electrolytes

Facilely prepared supramolecular ionogels can remain in the gel state at high temperature and exhibit high conductivity and relatively low activation energy.

Versatile, Reversible, and Reusable Gel of a Monocholesteryl Conjugated Calix[4]arene as Functional Material to Store and Release Dyes and Drugs Including Doxorubicin, Curcumin, and Tocopherol

Gels are interesting soft materials owing to their functional properties leading to potential applications. This paper deals with the synthesis of monocholesteryl derivatized calix[4]arene (G) and its instantaneous gelation at a minimum gelator concentration of 0.6% in 1:1 v/v THF/acetonitrile. The gel shows remarkable thermoreversibility by exhibiting Tgel→sol at ∼48 °C and is demonstrated for several cycles. The gel shows an organized network of nanobundles, while that of the sol shows spherical nanoaggregates in microscopy. A bundle with ∼12 nm diameter possessing hydrophobic pockets in itself is obtained from computationally modeled gel, and hence the gel is suitable for storage and release applications. The guest-entrapped gels exhibit the same microstructures as that observed with simple gels, while fluorescence spectra and molecular mechanics suggests that the drug molecules occupy the hydrophobic pockets. All the entrapped drug molecules are released into water, suggesting a complete recovery of the trapped species. The reusability of the gel for the storage and release of the drug into water is demonstrated for four consecutive cycles, and hence the gel formed from G acts as a functional material that finds application in drug delivery.

Poly(ionic liquid)/ionic liquid/graphene oxide composite quasi solid-state electrolytes for dye sensitized solar cells

A composite gel electrolytes containing poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide), 1-propyl-3-methylimidazolium iodide and graphene oxide are prepared for dye-sensitized solar cells, without any volatile organic solvent.

A novel colloidal suspension of TBA+BF4−–EG and its applications as a soft solid electrolyte

A novel ionically conducting colloidal suspension was prepared from a quaternary ammonium salt and ethylene glycol.