Solvent-free Liquid Research Articles

Powerful tailoring effects of counterions of ammonium surfactants on the phase transitions of solvent-free DNA thermotropic liquid crystals

Solvent-free DNA-surfactant thermotropic liquid crystals (TLCs) are new developed soft biomaterials in recent years. The phase transition behaviors of these DNA TLCs could be regulated by the chain lengths of used double chain surfactants. While, the impact of counterions of ammonium surfactants on the phase transitions of DNA TLCs is still not clear. Herein, a series of ammonium surfactants with different counterions were prepared and put into use of fabrication of DNA TLCs. With inorganic counterions, the resulted DNA materials exhibit distinct decrease on the thermodynamic stability of LC states along with the size increase of counterions, while, the use of planar p-toluenesulfonate as counterion leads to remarkable increased LC thermostability for the resulted DNA material, due to the different interaction between counterions and surfactant layers. These observations indicate that the LC property of DNA-surfactant complexes could be conveniently tailored by using surfactants with designed counterions, providing a new strategy for designing advanced solvent-free biomaterials.

Photocross-Linked Antimicrobial Amino-Siloxane Elastomers.

Mechanically robust bulk antimicrobial polymers are one way to address disease transmission via contaminated surfaces. Here, we demonstrate the visible light photo-oxidative cross-linking of amine-containing PDMS using a single-component, solvent-free system where amines have a dual role as antimicrobial functionalities and cross-linking sites. Rose Bengal, a xanthene dye used as a fluorescent stain, is thermally reacted with the polymer to give a solvent-free liquid siloxane that can generate reactive singlet oxygen upon aerobic green light irradiation, coupling the amine functionalities into imine cross-links. Photorheological experiments demonstrate that light intensity is the largest kinetic factor in the photo-oxidative curing of these polymers. Room temperature irradiation under an ambient atmosphere results in free-standing elastic materials with mechanical properties that depend on the amount of Rose Bengal present. An ultimate elongation strain of 117% and Young's modulus of 2.15 MPa were observed for the highest dye loading, with both mechanical properties found to be higher than those for the same solution-based dye amounts. We demonstrate that the solvent-free nature of the material can be exploited to generate 3D structures using low-temperature deposition as well as direct-write patterning and photolithography on glass substrates. The antimicrobial activity was investigated, with the cross-linked material demonstrating greater efficacy against E. coli (Gram negative) compared with MRSA (Gram positive) bacterial strains and inducing complete cell lysis of incubated CHO-K1 mammalian cells, demonstrating applicability as a mechanically robust single-component antimicrobial elastomer.

Extraction of estrogen hormones from water samples using an aqueous two-phase system: A new approach for sample preparation in the analysis of emerging contaminants

In this study, an environmentally friendly method of extracting steroid hormones, 17α-ethinylestradiol, levonorgestrel, gestodene, cyproterone acetate and estradiol valerate, using an aqueous two-phase system was developed. The aqueous two-phase system was applied as an organic solvent-free liquid–liquid extraction technique for the determination of these compounds by UV–Vis spectrophotometry in environmental samples. The experimental conditions were evaluated through the pH value of the medium (3.00–11.0), the nature of the electrolyte and polymer forming the system, the tie-line length (26.76–62.53% w/w), the temperature (278.15–313.15 K), and the mass ratio between the bottom and top phases of the system (1–5). The recovery efficiency was evaluated using the partition coefficient and the analytical signal of each hormone in the top phase. The study was carried out through univariate and multivariate optimization and, for the first time, interactions of tie-line length, polymer forming the system and temperature were observed, and these directly influenced the partition of hormones in aqueous two-phase system. An overall experimental condition for the recovery of all hormones simultaneously (L35 + Na2SO4 + H2O, at pH = 3.00, tie-line length = 64.06% w/w, temperature = 298.15 K and mass ratio between the bottom and top phases of the system = 5) was determined. Partition coefficients (8.8 ± 0.8) to (4533 ± 48) were obtained for the hormones in samples of drinking water, samples from lake and river water, and filtered water from a water treatment plant. Thereby, the aqueous two-phase system proved to be an innovative and good organic solvent free liquid–liquid extraction of hormones in environmental samples.

A library of thermotropic liquid crystals of inorganic nanoparticles and extraordinary performances based on their collective ordering

Inorganic nanoparticles are widely investigated due to their unique and fascinating physical and chemical properties. However, due to the strong interparticle interactions, they generally form irreversible random aggregates with elevated temperatures. This limits their technological applications considerably as the latter requires structural ordering and tunability. To address this, a versatile method of preparing solvent-free thermotropic liquid crystals of inorganic nanoparticles is presented. By chemically modifying the nanoparticles with a flexible organic surface layer, the nanoparticles self-assemble into ordered microstructures, possessing both ordering and fluidity in a solvent-free condition. A library of thermotropic liquid crystals, including 6 different shapes, 8 different compositions, and 18 different dimensions, is constructed. The flexible tuning of the particle properties and the intrinsic ordering and fluidity provide a powerful platform for the design and development of functional materials and devices with unique properties, such as polarization-dependent excitation, polarized photoluminescence, polarized photothermal response, and designable magnetic robot. • A versatile method of preparing solvent-free thermotropic liquid crystals of inorganic nanoparticles is presented. • A library of solvent-free TLCs of inorganic NPs, including 6 shapes, 8 compositions, and 18 dimensions, is constructed. • The intrinsic ordering and fluidity provide a platform for the design and development of functional materials and devices.

Preparation and application of solvent-free liquid proteins with enhanced thermal and anhydrous stabilities

This perspective details a robust chemical modification strategy to protect proteins from temperature, aggregation, and non-aqueous environments.

Electrochemistry of Solvent-Free Liquid Quinones

Redox flow batteries are a promising candidate for grid energy storage due favorable scaling and cyclability but are limited by low energy density due to poor solubility of active species in both aqueous and organic solvent. To increase the energy density we investigate the use of a solvent free liquid quinone electrolyte, resulting in high active species concentration (>10M). Well studied in aqueous and organic solvents, the electroreduction of quinones has been shown to strongly depend on the solvent [1] and supporting electrolyte [2]. The absence of inert solvent poses additional challenges due to mass transport and reaction effects in highly concentrated solutions [3]. Here we characterize the physical and electrochemical properties of 2,3,5-trimethyl-1,4-benzoquinone, ranging in concentration from a dilute solution in inert organic solvent to a highly concentrated solvent-free liquid quinone. Using ultramicroelectrode techniques, diffusion and redox kinetics are determined for solvated and solvent free liquid quinones to investigate the feasibility of this material for use as a solvent free redox flow battery electrolyte.

Bright Solvent-Free Luminescent Liquid with Magnetism Composed of a Thiocyanate Complex of Ce(III).

Ionic liquids composed of a thiocyanate complex of Ce(III) exhibit bright cyan photoluminescence with a quantum yield close to 40% in addition to paramagnetism. The morphology of a droplet of ionic liquid changes in response to solvent vapor as a stimulus. The emission lifetime and thermal property are characterized. The Weiss temperature is evaluated from the magnetic property measurements, which indicates that antiferromagnetic exchange interaction exists between Ce(III) ions. Insight into the characteristics of the electronic transitions in the Ce(III) complex is obtained using quantum chemical calculations. Thiocyanate complexes of Ce(III) are demonstrated as promising building blocks to produce solvent-free luminescent functional materials.

Engineered Anisotropic Fluids of Rare-Earth Nanomaterials.

The self-assembly of inorganic nanoparticles into well-ordered structures in the absence of solvents is generally hindered by van der Waals forces, leading to random aggregates between them. To address the problem, we functionalized rigid rare-earth (RE) nanoparticles with a layer of flexible polymers by electrostatic complexation. Consequently, an ordered and solvent-free liquid crystal (LC) state of RE nanoparticles was realized. The RE nanomaterials including nanospheres, nanorods, nanodiscs, microprisms, and nanowires all show a typical nematic LC phase with one-dimensional orientational order, while their microstructures strongly depend on the particles' shape and size. Interestingly, the solvent-free thermotropic LCs possess an extremely wide temperature range from -40 °C to 200 °C. The intrinsic ordering and fluidity endow anisotropic luminescence properties in the system of shearing-aligned RE LCs, offering potential applications in anisotropic optical micro-devices.

Crack-Assisted Charge Injection into Solvent-Free Liquid Organic Semiconductors via Local Electric Field Enhancement.

Non-volatile liquid organic semiconducting materials have received much attention as emerging functional materials for organic electronic and optoelectronic devices due to their remarkable advantages. However, charge injection and transport processes are significantly impeded at interfaces between electrodes and liquid organic semiconductors, resulting in overall lower performance compared to conventional solid-state electronic devices. Here we successfully demonstrate efficient charge injection into solvent-free liquid organic semiconductors via cracked metal structures with a large number of edges leading to local electric field enhancement. For this work, thin metal films on deformable polymer substrates were mechanically stretched to generate cracks on the metal surfaces in a controlled manner, and charge injection properties into a typical non-volatile liquid organic semiconducting material, (9-2-ethylhexyl)carbazole (EHCz), were investigated in low bias region (i.e., ohmic current region). It was found that the cracked structures significantly increased the current density at a fixed external bias voltage via the local electric field enhancement, which was strongly supported by field intensity calculation using COMSOL Multiphysics software. We anticipate that these results will significantly contribute to the development and further refinement of various organic electronic and optoelectronic devices based on non-volatile liquid organic semiconducting materials.

The conversion of nanocellulose into solvent-free nanoscale liquid crystals by attaching long side-arms for multi-responsive optical materials

Solvent-free nanoscale liquid crystals, featuring nanocellulose as the stiff core and long side-arms as the soft shell, showed unique flowability and responsiveness.

Mobility boost up of hybrid TFT with solvent-free cross-linked polyurethane-ionic liquid gate dielectric

We proposed solvent-free cross-linked ion gel polymer as a high-κ gate dielectric composed with polyurethane terminated with acrylate functional group and ionic liquids (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) through ultra violet curing (UV-cured IL-PU). Free-standing UV-cured IL-PUs were applied as gate insulator by conformally contacting on the amorphous indium gallium zinc oxide side-gate structure thin film transistor with a simple ex situ method. The device shows a dramatic improvement of electrical performances even under low operating voltage conditions; on/off ratio ∼104, field effect mobility at linear region 47.79 ± 17.65 cm2 V−1 s−1, sub-threshold swing 145.54 ± 16.65 mV decade−1 at VDS = 0.1 V and VGS sweep from −3 to 2 V.

Soft chromophore featured liquid porphyrins and their utilization toward liquid electret applications

Optoelectronically active viscous liquids are ideal for fabricating foldable/stretchable electronics owing to their excellent deformability and predictable π-unit–based optoelectronic functions, which are independent of the device shape and geometry. Here we show, unprecedented ‘liquid electret’ devices that exhibit mechanoelectrical and electroacoustic functions, as well as stretchability, have been prepared using solvent-free liquid porphyrins. The fluidic nature of the free-base alkylated-tetraphenylporphyrins was controlled by attaching flexible and bulky branched alkyl chains at different positions. Furthermore, a subtle porphyrin ring distortion that originated from the bulkiness of alkyl chains was observed. Its consequences on the electronic perturbation of the porphyrin-unit were precisely elucidated by spectroscopic techniques and theoretical modelling. This molecular design allows shielding of the porphyrin unit by insulating alkyl chains, which facilitates its corona-charged state for a long period under ambient conditions.

Multi-component eutectic salts to enhance the conductivity of solvent-free ionic liquid electrolytes for dye-sensitized solar cells

Ionic liquids (ILs) possess intrinsic nonvolatility, low flammability, high ionic conductivity, high thermal and chemical stability, rendering themselves as excellent candidates for next generation dye-sensitized solar cells (DSSCs). Further improving the ionic conductivity of ionic liquid electrolytes is critical to the performance enhancement of DSSCs. Here, multi-component eutectic salts by mixing four ILs are proposed to achieve higher ionic conductivity compared to the individual one. In addition, the effect of mixing strategy on the eutectic salts was systematically investigated by diverse structural, thermal, electrochemical and photovoltaic characterization in detailed. It revealed that mixing strategy could not only tune the solid-state property of individual ILs to liquid-state eutectic salts, but also greatly improve the ionic conductivity of final multi-component eutectic salts. Thus, based on the multi-component eutectic salt, a power conversion efficiency (PCE) of 4.81% could be obtained by the resultant device. Moreover, the DSSCs with multi-component eutectic salt also display better stability than the referenced device with volatile organic solvent. The mixing eutectic salts offer us a feasible strategy to design high ionic conductive electrolytes for high performance dye-sensitized solar cells.

Insight into the Structure and Activity of Surface-Engineered Lipase Biofluids.

Despite a successful application of solvent-free liquid protein (biofluids) concept to a number of commercial enzymes, the technical advantages of enzyme biofluids as hyperthermal stable biocatalysts cannot be fully utilized as up to 90-99% of native activities are lost when enzymes were made into biofluids. With a two-step strategy (site-directed mutagenesis and synthesis of variant biofluids) on Bacillus subtilis lipase A (BsLA), we elucidated a strong dependency of structure and activity on the number and distribution of polymer surfactant binding sites on BsLA surface. Here, it is demonstrated that improved BsLA variants can be engineered via site-mutagenesis by a rational design, either with enhanced activity in aqueous solution in native form, or with improved physical property and increased activity in solvent-free system in the form of a protein liquid. This work answered some fundamental questions about the surface characteristics for construction of biofluids, useful for identifying new strategies for developing advantageous biocatalysts.

Paintable Room-Temperature Phosphorescent Liquid Formulations of Alkylated Bromonaphthalimide.

Organic phosphors have been widely explored with an understanding that crystalline molecular ordering is a requisite for enhanced intersystem crossing. In this context, we explored the room-temperature phosphorescence features of a solvent-free organic liquid phosphor in air. While alkyl chain substitution varied the physical states of the bromonaphthalimides, the phosphorescence remained unaltered for the solvent-free liquid in air. As the first report, a solvent-free liquid of a long swallow-tailed bromonaphthalimide exhibits room-temperature phosphorescence in air. Doping of the phosphor with carbonyl guests resulted in enhanced phosphorescence, and hence a large-area paintable phosphorescent liquid composite with improved lifetime and quantum yield was developed.

A solvent-free porous liquid comprising hollow nanorod-polymer surfactant conjugates.

Liquids having permanent porosity can offer significant processing advantages over their solid counterparts. This has recently led to tremendous activity towards the design and development of intrinsic pores in the liquid phase, predominantly for studies involving gas sequestration. We show here the development of a solvent-free mesoporous liquid material based on anisotropic “hollow-core and silica-shell” nanorods conjugated with polymer surfactant chains, which can sequester CO2 gaseous molecules at 0 °C. Hollow silica nanorods (SiNRs) with average aspect ratios of 2.5, 8, and 11 (as obtained by transmission electron microscopy (TEM) and small angle X-ray scattering) were synthesized using a surfactant-templating methodology, and fluidity/flow processability were imparted by a three-step process involving covalent coupling of an organosilane (OS) canopy to form OS@SiNR, followed by electrostatic grafting of polymer surfactant (PS) chains to the organosilane, and subsequent removal of solvent to provide a solvent-free composite, PS-OS@SiNR. Differential scanning calorimetric and frequency sweep rheological measurements of PS-OS@SiNR indicated melting transition between 15 and 20 °C, while thermal gravimetric analysis showed ca. 20 w/w% silica content (i.e. 9.5% volume fraction of silica and containing ca. 3% volume fraction as voids). As observed using TEM, the surface modification of the nanorods resulting in the formation of PS-OS@SiNR does not lead to blockage of the hollow core. We show that whilst N2 adsorption in the porous liquid is hindered due to the glassy polymer-surfactant layer at −196 °C, CO2 adsorption at 0 °C showed 3.3–4.8 w/w% gas uptake. Overall we demonstrate the synthesis of an anisotropic porous liquid which not only sequesters CO2 but also has the ability to flow like a liquid.

Charge transfer liquid: a stable donor-acceptor interaction in the solvent-free liquid state.

Charge-transfer complexes have been an inspiration to develop many functional soft materials. However, most of those studies have focused on solution based assemblies wherein the explicit control of solvents and their polarity are crucial. In this context, we explore an efficient and stable charge transfer liquid using a solvent-free liquid dialkoxynaphthalene donor and a naphthalenediimide acceptor. It has been observed that irrespective of the donor-acceptor ratio, the charge-transfer liquid exhibited an unprecedented stability and retained characteristic features even at increased temperatures. The underlying intermolecular interactions leading to efficient CT have been examined by NMR techniques together with theoretical modelling studies. The concept of charge transfer liquid will be highly beneficial for the development of processable optoelectronically active materials.

Model-based scale-up and reactor design for solvent-free synthesis of an ionic liquid in a millistructured flow reactor

Based on kinetic investigations in microreactors, a millistructured plate reactor for a solvent-free ionic liquid synthesis was designed by combining several scale-up concepts to maintain thermal stability.

Solvent-free lithium and sodium containing electrolytes based on pseudo-delocalized anions.

Mixing the standard battery salt LiTFSI with various Li-salts of novel pseudo-delocalized organic anions [N(CH3)2((CH2)nSO3)((CH2)mSO3)]- (MMnm11), results in super-cooled solvent-free liquid electrolytes with glass transition temperatures of ca. 50 °C. Synthesis routes and full chemical characterisation of the new pseudo-delocalized anions are presented, as well as phase and thermal stabilities. The ion conductivities and electrochemical stabilities are evaluated towards lithium and sodium battery application.

Differential capacitance of ionic liquids according to lattice-gas mean-field model with nearest-neighbor interactions.

The Bragg-Williams free energy is used to incorporate nearest-neighbor interactions into the lattice gas model of a solvent-free ionic liquid near a planar electrode. We calculate the differential capacitance from solutions of the mean-field consistency relation, arriving at an explicit expression in the limit of a weakly charged electrode. The two additional material parameters that appear in the theory-the degree of nonideality and the resistance to concentration changes of each ion type-give rise to different regimes that we identify and discuss. As the nonideality parameter, which becomes more positive for stronger nearest-neighbor attraction between like-charged ions, increases and the electrode is weakly charged, the differential capacitance is predicted to transition through a divergence and subsequently adopt negative values just before the ionic liquid becomes structurally unstable. This is associated with the spontaneous charging of an electrode at vanishing potential. The physical origin of the divergence and the negative sign of the differential capacitance is a nonmonotonic relationship between the surface potential and surface charge density, which reflects the formation of layered domains alternatingly enriched in counterions and coions near the electrode. The decay length of this layered domain pattern, which can be many times larger than the ion size, is reminiscent of the recently introduced concept of "underscreening."