Research on electrochemical properties of nonaqueous ionic liquid microemulsions

The nonaqueous ionic liquid (IL) microemulsions composed of 1-butyl-3-methylimidazolium tetrafluoroborate, Triton X-100, and toluene were prepared and the electrochemical properties of the nonaqueous IL microemulsions were investigated in this paper. It is shown that characteristics of the nonaqueous IL microemulsions such as electrical conductivity, electrochemical window, and solubility are good, which indicate that the nonaqueous IL microemulsions can be used as electrolyte for electrochemical research. The electrochemical properties of the nonaqueous IL microemulsions were researched by cyclic voltammetry (CV) and electrochemical impedance spectroscopy methods using potassium ferricyanide as electroactive probe. It was found that the reversibility was better and the peak current densities of CV were higher for the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ electrode reaction in the nonaqueous IL microemulsions than those in IL. However, the electrochemical behavior of the probe in the nonaqueous IL microemulsions with different microenvironments (oil-in-IL, IL-in-oil, and bicontinuous) was different. The electrochemical property of the probe in the oil-in-IL microemulsion was the best, which was studied in detail.     

Design and fabrication of liquid crystal-based lenses

ABSTRACT

Liquid crystal (LC)-based lenses are promising for a wide range of applications from optical communications and signal processing to three-dimensional displays. Among a variety of the LC-based lenses, several classes including the Fresnel type and the lenticular type are comprehensively reviewed from the standpoints of the basic concepts and the device architectures. The underlying mechanisms for the focusing effect and the tuning capability inherent to the lens configuration are described. Recent progress on the LC-based lenses for reconfigurable optical processing and autostereoscopic displays is also presented. The lens architecture combined with the intrinsic anisotropy of the LC provides a versatile platform to build up high-performance LC-based lenses with the tuning capability.     

Developing liquid crystal-based immunoassay for melamine detection

Research on Chemical Intermediates - We have developed a liquid crystal (LC)-based immunoassay for melamine detection by using direct, sandwich and competitive formats. The detection mechanism was...     

Microregion detection of ionic liquid microemulsions

Nonaqueous ionic liquid (IL) microemulsion consisting of IL, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), surfactant TX-100, and toluene was prepared and the phase behavior of the ternary system was investigated. Electrical conductivity measurement was used for investigating the microregions of the nonaqueous IL microemulsions. On the basis of the percolation theory, the bmimBF(4)-in-toluene (IL/O), bicontinuous, and toluene-in-bmimBF(4) (O/IL) microregions of the microemulsions were successfully identified using insulative toluene as the titration phase. However, this method was invalid when conductive bmimBF(4) acted as the titration phase. The microregions obtained by conductivity measurements were further proved by electrochemical cyclic voltammetry experiments. The results indicated that the conductivity method was feasible for identifying microstructures of the nonaqueous IL microemulsions.     

Novel microemulsions: ionic liquid-in-ionic liquid

The hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) can be dispersed in hydrophilic IL propylammonium formate (PAF) with the aid of surfactant AOT, and [bmim][PF(6)]-in-PAF microemulsions are formed.     

Carbon dioxide in ionic liquid microemulsions

Tailor-made emulsion: A CO(2) -in-ionic-liquid microemulsion was produced for the first time. The CO(2) -swollen micelles are "tunable" because the micellar size can be easily adjusted by changing the pressure of CO(2) . The microemulsion has potential applications in materials synthesis, chemical reactions, and extraction.     

液晶分子印迹整体柱的制备及其分子识别热力学

液晶分子印迹聚合物(MIPs)因刚性液晶单体的加入而在超低交联度水平下也能印迹和识别模板分子,有效解决了传统MIPs因高交联度造成的位点包埋、结合容量低、传质慢等问题.尽管液晶MIPs具有如此独特的优势,但却面临着由于交联度的大幅度降低而导致印迹效果下降的问题.为了研究液晶MIPs的结合特性,制备具有良好印迹效果的低交...     

Emulsified microemulsions and oil-containing liquid crystalline phases

Self-assembled nanostructures, such as inverted type mesophases of the cubic or hexagonal geometry or reverse microemulsion phases, can be dispersed using a polymeric stabilizer, such as the PEO-PPO-PEO triblock copolymer Pluronic F127. The particles, which are described in the present study, are based on monolinolein (MLO)-water mixtures. When adding tetradecane (TC) to the MLO-water-F127 system at constant temperature, the internal nanostructure of the kinetically stabilized particles transforms from a Pn3m (cubosomes) to a H2 (hexosomes) and to a water-in-oil (W/O, L2) microemulsion phase (emulsified microemulsion (EME)). To our knowledge, this is the first time that the formation of stable emulsified microemulsion (EME) systems has been described and proven to exist even at room temperature. The same structural transitions can also be induced by increasing temperature at constant tetradecane content. The internal nanostructure of the emulsified particles is probed using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). At each investigated composition and temperature, the internal structure of the dispersions is observed to be identical to the corresponding structure of the nondispersed, fully hydrated bulk phase. This is clear evidence for the fact that the self-assembled inner particle nanostructure is preserved during the dispersion procedure. In addition, the internal structure of the particles is in thermodynamic equilibrium with the surrounding water phase. The internal structure of the dispersed, kinetically stabilized particles is a "real" and stable self-assembled nanostructure. To emphasize this fact, we denoted this new family of colloidal particles (cubosomes, hexosomes, and EMEs) as "ISASOMES" (internally self-assembled particles or "somes").     

Ionic liquid crystal-based electrolyte with enhanced charge transport for dye-sensitized solar cells

A room temperature ionic liquid crystal,1-dodecyl-3-ethylimidazolium iodide(C12EImI),and an ionic liquid,1-decyl-3-ethylimidazolium iodide(C10EImI),have been synthesized,characterized and employed as the electrolyte for dye-sensitized solar cells(DSSC).The physicochemical properties show that a smectic A(SmA)phase with a lamellar structure is formed in C12EImI.Both C12EImI and C10EImI have good electrochemical and thermal stability facilitating their use in DSSC.The steady-state voltammograms reveal that the diffusion coefficient of I3–in C12EImI is larger than that in C10EImI,which is attributed to the existence of the SmA phase in C12EImI.Because the iodide species are located between the layers of imidazolium cations in C12EImI,exchange reaction-based diffusion is increased with a consequent increase in,the overall diffusion.The electrochemical impedance spectrum reveals that charge recombination at the dyed TiO2/electrolyte interface of a C12EImI-based DSSC is reduced due to the increase in I3–diffusion,resulting in higher open-circuit voltage.Moreover,both short-circuit current density and fill factor of the C12EImI based DSSC increase,as a result of the increasing transport of I3–in C12EImI.Consequently,the photoelectric conversion efficiency of C12EImI-based DSSC is higher than that of the C10EImI–based DSSC.     

An HII liquid crystal-based delivery system for cyclosporin A: physical characterization

In the present study we demonstrate that large quantities of cyclosporin A and three dermal penetration enhancers (phosphatidylcholine, ethanol, or Labrasol) can be solubilized into reverse hexagonal (HII) liquid crystalline structures composed of monoolein, tricaprylin, and water. The microstructural characteristics of these complex multi-component systems were elucidated by rheological, SAXS, and DSC measurements. Addition of up to 20 wt% phosphatidylcholine improved significantly the elastic properties of the systems (lower values of tandelta) and increased the thermal stability of the mesophases enabling us to solubilize up to 6 wt% cyclosporin A and two other enhancers (Labrasol and ethanol) to obtain stable mesophases at physiological temperature. Rheological measurements revealed that solubilization of cyclosporin A alone has a destabilizing effect on the reverse hexagonal phases: it caused a deterioration in the elastic properties of the systems, leading to more liquid-like behavior and resulting in very short relaxation times (0.04-0.1 s). Labrasol, solubilized at high concentrations (up to 12 wt%) into the liquid crystals, also demonstrated a destabilizing effect on the HII structure: the decreasing elasticity of the system was attributed to Labrasol's presumed locus at the interface and its ability to bind water, as shown by DSC measurements. Ethanol had a destabilizing effect similar to that of Labrasol, yet the effect appeared to be more pronounced, probably due to its higher water-binding capability.     

Comparison of electrodeposition of silver in ionic liquid microemulsions

Both ionic liquid (IL) and water are typical green solvents and have high electric conductivity. The use of IL microemulsions as templates and media for electrochemical synthesis of nano-materials is attractive. In this work, water-in-ionic liquid (W/IL) microemulsion and ionic liquid-in-water (IL/W) microemulsion were prepared, in which hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was used. The cyclic voltammetry (CV) behavior and electroplating in the W/IL and IL/W microemulsion systems containing silver nitrate were investigated for the first time. Both the CV curves exhibit the presence of reduction and oxidation peaks corresponding to the deposition and dissolution of silver from the two microemulsion systems. However, the CV obtained from IL/W microemulsion system exhibits a crossover, which is different from that obtained from W/IL microemulsion system. The electrodeposits obtained from W/IL microemulsion system are nano-granular, while those obtained from IL/W microemulsion system are planar. These results are attributed to the different microenvironments of the microemulsions.     

A new liquid crystal-based method to study disruption of phospholipid membranes by sodium deoxycholate

In this study, we have used liquid crystals (LCs) to investigate the mechanism and dynamics of structural change of phospholipid membranes caused by sodium deoxycholate (NaDC). Addition of the NaDC aqueous solution to the phospholipid [1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG)] modified aqueous/LC interface resulted in the interaction-induced change of the orientational arrangement of the LCs from a homeotropic state to a planar state. The importance of contributing parameters was determined by observing the changes in the orientation of LCs. We showed that this interaction was affected by reaction time, reaction pH, concentration of NaDC and the presence of cholesterol. Moreover, the phospholipid membrane, which became defective after being exposed to NaDC, was capable of self-repairing by excess Tris-buffered saline solution, indicating that the reaction of NaDC with the phospholipid membrane is reversible. The obtained results proved the feasibility of the method deploying the DOPG/LC interface to monitor the membrane reaction stemming from the interaction between a bioactive molecule and a phospholipid membrane.     

Synthesis and properties of polyampholytes prepared in microemulsions

A series of polyampholytes of sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (MADQUAT) has been synthesized by polymerization in microemulsions. The reaction products are stable inverse latexes consisting of high molecular weight copolymers entrapped in water droplets of small size (d % 80 nm) and dispersed in an isoparaffinic oil. The optimization of the formulation was by a selection procedure based on the hydrophile-lipophile balance of the emulsifiers and solubility parameters of the different components. Both ionomers play an important role in the formulation owing to their amphiphilic and electrolyte characters. Reactivity parameter studies yield r_A and r_M values of 0.81 and 1.97 for NaAMPS and MADQUAT, respectively. The properties of polyampholytes in pure water and in salt solutions were investigated by turbidimetry and viscometry experiments. The results are compared with the recently developed theory of Higgs and Joanny (J. Chem. Phys. 94, 1543 (1991)).     

Diffusion behavior of pharmaceutical O/W microemulsions studied by dynamic light scattering

Dynamic light scattering experiments have been performed at various concentrations, of pharmaceutical oil-in-water microemulsions consisting of Eutanol G as oil, a blend of a high (Tagat O2) and a low (Poloxamer 331) hydrophilic–lipophilic balance surfactant, and a hydrophilic phase (propylene glycol/water). We probe the dynamics of these microemulsions by dynamic light scattering. In the measured concentration range, two modes of relaxation were observed. The faster decaying mode is ascribed classically to the collective diffusion D _c (total droplet number density fluctuation). We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of polydispersity fluctuations. The diffusion coefficient associated with this mode is then the self-diffusion D _s of the droplets. It was found that D _c and D _s had opposite volume fractions of oil plus surfactants (ϕ) dependence and a common limiting value D ₀ for ϕ=0. Average hydrodynamic radius (R _h=10.5 nm) of droplets was calculated from D ₀. R _h is supposed to compose the inner core, a surfactant film including possible solvent molecules, which migrate with the droplet. The concentration dependence of diffusion coefficients reflects the effect of hard sphere and the supplementary repulsive interactions which arises due to loss of entropy, when absorbed chains of surfactant intermingle on the close approach of the two droplets. This mechanism could also explain the observed stability of our systems. The estimated extent of polydispersity is 0.22 from the amplitude of slower decaying mode. The polydispersity in microemulsion systems is dynamic in origin. Results indicate that the time scale for local polydispersity fluctuations is at least three orders of magnitude longer than the estimated time between droplet collisions.     

Structural properties of palladium nanoparticles embedded in inverse microemulsions

Pd nanoparticles were synthesized by reduction of palladium acetate by ethanol in systems containing tetrahydrofuran (THF) as dispersion medium and tetradodecylammonium bromide (TDABr) surfactant as stabilizer. The polar phase (ethanol) acts at the same time as reducing agent. THF/TDABr/H₂O inverse microemulsions containing micelles of various sizes were also prepared, and the structure of complex liquids was studied by density measurements. Sols containing nanosize Pd⁰ particles were synthesized within the water droplets of this micellar system. The stabilized Pd⁰/surfactant system was characterized by density measurements, absorption spectroscopy, and transmission electron microscopy. The stabilizing surfactant layer adsorbed on the liquid/liquid interface and on the surface of the nanoparticles (i.e., the liquid/solid interface) significantly reduced the excess volume for the palladium nanodispersion in organic solvent. Received: 17 July 2000 Accepted: 5 October 2000     

Diffusion in ultrathin liquid films

Inhomogeneous molecular diffusion in layered structures of thin liquid films deposited on solid surfaces is observed via wide field single molecule microscopy. The fluorescence dyes Rhodamine 6G and Oregon Green 514 are used to probe the diffusion in tetrakis(2-ethylhexoxy)-silane and polydimethylsiloxane. A broad distribution of diffusion constants is observed which can be attributed to diffusion within distinct layers of the liquid. Comparison with computer simulations shows that diffusion is normal but depends strongly on the distance of the molecules from the solid surface. Diffusion within layers is faster than between the layers and additional temperature activation is necessary to speed up interlayer diffusion.     

Thermoanalytical investigation of lyotropic liquid crystals and microemulsions for pharmaceutical use

The interactions between surfactant and water were studied thermoanalytically focusing on the lyotropic liquid crystalline and microemulsion region in four ternary systems containing Cremophor EL and Cremophor RH40 as surfactants, neutral oil and isopropyl myristate as oily components. Subzero temperature DSC (SZT-DSC) measurements were carried out to determine the quantity of the bound water forming a hydration layer in surfactant microstructures, and the amount of free water, which has physico-chemical properties not much different from those of pure water. The variation of the surfactant:bound water ratio in the function of water concentration was also investigated. Phase changes detected by the SZT-DSC measurements were confirmed by polarization-microscopic and rheological investigations.     

Transport properties of alternative fuel microemulsions based on sugar surfactant

Electrical conductivity of fuel microemulsion composed of diesel, pentanol, water, and sucrose laurate as surfactant was investigated over a wide range of water contents varying from 0 to 90?wt% and temperature varying from 10°C to 50°C. Conductivity measurements were performed on samples, the composition of which lie along the one-phase channel using a conductivity meter. Activation energy of conduction flow was evaluated. The hydrodynamic radius as a function of temperature in the aqueous phase-rich region (90?wt%) was measured using the dynamic light scattering (DLS) method. The microstructure of the microemulsion was further investigated by NMR diffusometry by which the self-diffusion coefficients for water were determined at 25°C. Electrical conductivity increases with water content up to 40?wt% and the percolation threshold was observed, and then stabilizes between 40 and 80?wt% then decreases. Percolation threshold temperature at constant composition was monitored as 36°C for water contents below 80?wt% and as 34°C for water contents above that. As predicted by the conductivity measurements, the determined self-diffusion coefficients of water confirmed the structural transition from discrete W/O droplets to bi-continuous phase and finally to O/W droplet microemulsion.     

Diffusion measurements in chiral liquid crystals

Abstract

We present results of diffusion investigations in twisted nematics (nematic-cholesteric mixtures). The dependence of the diffusion coefficient along the helix on the concentration of the cholesteric compound, the sample temperature and the diffusion time are measured by a new nuclear magnetic resonance method. The diffusion coefficient was found to decrease with diffusion time in the studied range of about 0·5–50 ms. The results are consistent with data from ¹³C-N.M.R. experiments, and with field gradient measurements by other authors.