Surfactant Liquid Crystals Research Articles

Facile assembly of flexible, stretchable and attachable symmetric microsupercapacitors with wide working voltage windows and favorable durability

With the increasing development of intelligent robots and wearable electronics, the demand for high-performance flexible energy storage devices is drastically increasing. In this study, flexible symmetric microsupercapacitors (MSCs) that could operate in a wide working voltage window were developed by combining laser-direct-writing graphene (LG) electrodes with a phosphoric acid-nonionic surfactant liquid crystal (PA-NI LC) gel electrolyte. To increase the flexibility and enhance the conformal ability of the MSC devices to anisotropic surfaces, after the interdigitated LG formed on the polyimide (PI) film surface, the devices were further transferred onto a flexible, stretchable and transparent polydimethylsiloxane (PDMS) substrate; this substrate displayed favorable flexibility and mechanical characteristics in the bending test. Furthermore, the electrochemical performances of the symmetric MSCs with various electrode widths (300, 400, 500 and 600 μm) were evaluated. The findings revealed that symmetric MSC devices could operate in a large voltage range (0–1.5 V); additionally, the device with a 300 μm electrode width (MSC-300) exhibited the largest areal capacitance of 2.3 mF cm−2 at 0.07 mA cm−2 and an areal (volumetric) energy density of 0.72 μWh cm−2 (0.36 mWh cm−3) at 55.07 μW cm−2 (27.54 mW cm−3), along with favorable mechanical and cycling stability. After charging for ~20 s, two MSC-300 devices connected in series could supply energy to a calculator to operate for ~130 s, showing its practical application potential as an energy storage device. Moreover, the device displayed favorable reversibility, stability and durability. After 12 months of aging in air at room temperature, its electrochemical performance was not altered, and after charging-discharging measurements for 5000 cycles at 0.07 mA cm−2, ~93.6% of the areal capacitance was still retained; these results demonstrated its practical long-term application potential as an energy storage device.

Chemical deposition from a liquid crystal template: A highly active mesoporous nickel phosphate electrocatalyst for hydrogen green production via urea electro-oxidation in an alkaline solution

Recently the urea and urinated wastewater electrolysis process has shown promising technology for hydrogen fuel green production in addition to denitrification of wastewater. However, to make the process economically valuable, the electrocatalysts nanoarchitecture, nanometer size, shape, facets, and composition need to be engineered to boost the urea oxidation reaction (UOR). This work demonstrates a simple and novel approach to the synthesis of mesoporous nickel phosphate nanoparticles (meso-NiPO) via chemical deposition from a surfactant liquid crystal template. Typically, the nickel ions dissolved in the aqueous domain of the hexagonal liquid crystalline phase of the Brij®78 template were chemically reacted with the sodium phosphate solution to precipitate the mesoporous nickel phosphate nanoarchitecture after washing up the surfactant. The physicochemical characterizations show the meso-NiPO exhibits an amorphous highly mesoporous structure with a higher specific surface area (43.50 m2/g) compared to the bare nickel phosphate (bare-NiPO, 4.26 m2/g) prepared in the absence of surfactant. The electrochemical performance of meso-NiPO electrocatalyst for the urea oxidation reaction in alkaline solution exhibits superior activity including a lower oxidation onset potential (0.30 V vs. Ag/AgCl), charge transfer resistance (3.35 O) and mass activity of 700.7 mA/cm2 mg at the oxidation potential of 0.6 V vs. Ag/AgCl. Moreover, the meso-NiPO reveals long-term stability, and 97.5% of the steady-state oxidation current was maintained after the 3-hour urea electrolysis test. Using an H-shape urea electrolyzer, the corresponding cathodic hydrogen production rate reached 415 µmol/h and a Faradic efficiency of 96.8 % at an applied bias of 2.0 V. The electroactivity high performance of the mesoporous nickel phosphate is ascribed to the high specific surface area and mesoporous architecture that provide efficient charge transfer, as well as mass transport of the electroactive species. The chemical deposition from a surfactant liquid crystal template has the advantages of a one-pot template, applicable to the synthesis of a wide range of nanomaterials with various compositions and nanoarchitectures at room temperature for application in electrochemical energy production and storage systems.

Wide-Temperature-Range Flexible Micro-Supercapacitors Using Liquid Crystal Gel Electrolyte

In this work, to construct a sunlight-powered energy storage system, single wall carbon nanotubes (SWCNTs)-based symmetric micro-supercapacitors (MSCs) were fabricated by a one-step, facile spraying method. The electrodes exhibited satisfactory conductivity with a sheet resistance of 275 Ω/sq. Moreover, potassium hydroxide-poly(vinyl alcohol) (KOH-PVA) and phosphoric acid-nonionic surfactant liquid crystal (PA-NI LC) gel electrolytes were prepared and applied to design all-solid-state MSC devices. Compared to the device assembled using the SWCNTs/KOH-PVA gel electrolyte, the SWCNTs/PA-NI LC electrolyte displayed larger areal capacitance with the largest recorded value of 11.0 mF·cm–2 at a current density of 0.08 mA·cm–2 at room temperature. Additionally, the effect of temperature on the MSC device performance was assessed, and the results revealed that the device based on the SWCNTs/PA-NI LC electrolyte achieved enhanced electrochemical performance at an operating temperature of 65 °C, including a large areal capacitance of 14.7 mF·cm–2 at 0.08 mA·cm–2, a better rate performance of 88% with 12.9 mF·cm–2 at 0.4 mA·cm–2, and a higher energy density of 2.04 μWh·cm–2 at a power density of 40.64 μW·cm–2. In addition, the MSC device featured high cyclic stability under bending conditions (45 or 90°) at room temperature. Furthermore, a sunlight-powered energy storage system was fabricated, combining solar cells with the as-assembled MSC devices. Three MSCs connected in series were charged by solar cells and further acted as the energy supply for a red light-emitting diode (LED), which could be continuously operated for 2 min 30 s. All of the findings herein represent a good indication of the promising practical application potential of the as-prepared MSC devices as energy storage devices at high temperatures.

Dissolution of Lamellar Phases

Dissolution of surfactant liquid crystals is an important process both at the manufacturing stage of surfactant based formulated products and during their use. Dissipative particle dynamics simulations were employed to study the production of surfactant-oil-water systems under both temperature and water quenches. Upon the dissolution of a high concentration lamellar phase surfactant, wormlike micelles are formed, which differ from the spherical micelles produced at the same concentration with a temperature quench. The surfactant molecules have a tendency to remain within their initially formed lamellar phase sheets and just rearrange into wormlike micelles. When a hydrophobic additive (oil) is added to the initial system, longer cylindrical micelles are formed, with the creation of some spherical micelles under dissolution. These micelles detach from the long cylinders as a result of their natural oscillations.

Spectroscopic characterization of red perylimide/surfactant nanocomposites

Novel photoluminescent materials formed by some selected surfactants, metal derivatives of bis(2-ethylhexyl) sulfosuccinate (M(AOT)n; M = Na+, Co2+, Er3+ and Yb3+), bis(2-ethylhexyl) amine (BEEA), bis(2-ethylhexy1) phosphoric acid (HDEHP) and a 1:1 BEEA/HDEHP mixture, doped with the red perylimide (ROT-300) have been prepared, and their optical properties have been tested by absorption spectroscopy and steady state and time-resolved fluorescence. Experimental results show spectral shifts of the typical ROT-300 absorption and fluorescence bands with respect to that in apolar solvent medium. Data analysis leads consistently to attribute this feature mainly to the freezing of the diffusive movement of the dye molecules confined in the nanodomains of the surfactant liquid crystals, whilst minor effects can be due to interaction with the surfactant polar groups. Potentialities of these novel luminescent nanostructured composites as dye lasers, optical amplifiers and solar concentrators have been highlighted. In particular, under optical pumping using a pulse laser, amplified spontaneous fluorescence emission of the ROT-300/HDEHP system above an excitation energy threshold value of about 725 mJ cm−2 was observed.

ChemInform Abstract: Silica-Based, Cubic Mesostructures: Synthesis, Characterization, and Relevance for Catalysis

We review the formation mechanism, synthetic history and catalytic applications of the cubic phases of mesoporous silica. MCM-48 and SBA-1, analogous to surfactant lyotropic liquid crystal phases, possess a three-dimensional pore array, a 15–30 A pore aperture and a narrow pore size distribution. Evidence for intermediate range order within the silicate walls based on PAS-FTIR spectra will be discussed. Isomorphic heteroatom substitution of aluminum and a number of transition metals has been achieved by both hydrothermal and post-synthetic methods in order to modify the surface activity of these materials. Modified materials containing fully oxidized, early transition metals were found to be catalytically active for photocatalytic reduction of CO2 with water as well as peroxidative oxidation and halogenation of large organic substrates.

Co-Synthesis and Drug Delivery Properties of Mesoporous Hydroxyapatite-Silica Composites

In this work, mesoporous hydroxyapatite-silica (HA-silica) composite materials with four different Si:Ca:P ratios were sol-gel derived through self-assembly using triblock copolymer Pluronics P123 as template. The composition and mesoporous structure formed were characterized by X-ray diffraction and electron microscopy. The XRD patterns indicated that the intensity of the HA phase becomes stronger as the Ca/Si ratio of the composite increases. From nitrogen gas analysis at 77 K, type IV isotherm plots for typical mesoporous materials were observed for all of the samples. However, the mesoporous structure of HA-silica tends to becomes less ordered as the Ca/Si ratio increases. Promising consistency between the pore sizes from the Barrett, Joyner and Halenda (BJH) method, Transmission Electron Microscopy (TEM) and Small Angle X-ray diffraction (SAXRD) was also observed. The formation mechanism of mesoporous HA-silica composites was proposed, where the interaction between the crystallization of HA and the surfactant liquid crystal determines the regularity of the meso-structure. In vitro drug loading and release studies showed that drug loading capacity is dependent on the pore volume of the sample, and the mesoporosity of the samples were responsible for the sustained release of drugs. In vitro cell culture of the samples showed promising biocompatibility where osteosarcoma cells were observed to grow favourably on the synthesized composites.

One-pot synthesis of amino functionalized mesoporous silica materials: using simulations to understand transitions between different structures

The rich phase behavior of surfactants can be exploited to design materials with a given desired structure and properties. One example includes amino functionalized mesoporous silicas, which can be used in different environmental applications, including removal of heavy metals from water and CO2 separation and purification. These applications may require a high concentration of functional groups, but the increased concentration of hybrid organic–inorganic precursors can lead to the destruction of the liquid crystals or transformation into other phases. In this work, we modeled the phase behavior of such systems using lattice Monte Carlo simulations and analyzed the distribution of hybrid organic–inorganic precursors to explain the observed changes in the liquid crystal structures. In particular, we observed that if the hybrid precursor is sufficiently hydrophobic, it can act as a cosurfactant, swell the core of the surfactant liquid crystal, and lead to structures with smaller interfacial curvature. On the other hand, if the hybrid precursor acts as a cosolvent it will solubilize the surfactant leading to the destruction of the preformed liquid crystal.

Low temperature effect on the morphological control of mesoporous silica nanofibers at near-neutral pH: A biomimetic strategy

Silica biominerals with elaborate skeletons can be fabricated at mild conditions of near-neutral pH and low temperature through biosilicification. In this paper, a biomimetic way was reported by which hexagonally ordered mesoporous silica fibers were facilely synthesized. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations reveal high yield of the mesoporous silica fibers with diameter varying from 200 to 400 nm and mesopore channels parallel to the axes of the fibers. At near-neutral pH, low temperature of 283 K was proved to be essential to control the morphogenesis of the surfactant liquid crystal templated silica. X-ray diffraction (XRD) and nitrogen sorption measurements indicate that the silica nanofibers possess ordered hexagonal mesostructure and narrow pore size distribution. Both the structure and morphology are sensitive to the synthesis temperature. Synthesis at the temperature of 293 K led to decreasing of mesostructure regularity, as well as a transformation of morphology from nanofibers to particle aggregates.

Study of Confined 5-Aza[5]helicene in Ytterbium(III) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles

Some relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Moreover, when H5 is entrapped in Yb(DEHSS)3 reversed micelles, the combined action of this interaction and of confinement effects leads to marked changes of its photophysical properties with respect to those of H5 molecularly dispersed in apolar medium. The influence of the entrapment of finite amounts of H5 on the reversed micelle structure was investigated by SAXS. The analysis of experimental results brings to the hypothesis that H5 is preferentially solubilized and opportunely oriented in the micellar palisade layer and that its insertion causes an unidimensional growth of reversed micelles. From an analysis of WAXS spectra of H5/Yb(DEHSS)3 composites, obtained by complete evaporation of the volatile components of the H5/water/Yb(DEHSS)3/n-heptane solutions, it was ascertained that also on these systems H5 is dispersed molecularly or in a quite amorphous state in the surfactant liquid crystals without forming a separate crystalline nanophase.

Liquid Crystalline Phases and Other Microheterogeneous Systems as Media for Organic Synthesis

Reactant incompatibility is often a problem in organic synthesis. Here, we report an investigation of a nucleophilic substitution reaction, involving incompatible substrate and nucleophile, performed in three different self‐assembly systems, two liquid crystalline phases and one microemulsion, and also in slurries of finely divided mesoporous silica with either hexagonal or cubic symmetry. The reactants used were 4‐tert‐butylbenzyl bromide and potassium iodide. The reaction turned out to be extremely fast in the two liquid crystalline phases, intermediate in the mesoporous materials and somewhat slower—although still fast compared to the two‐phase system—in the microemulsion. The very high reactivity in the liquid crystalline phases is believed to be associated with the very high interfacial area of these systems. This work shows that surfactant liquid crystals can be used as minireactors for organic reactions. Removal of the surfactant after completed reaction is a practical problem, however, that needs to be taken into account.

Super‐Stable Nonaqueous Foams in Diglycerol Fatty Acid Esters—Non Polar Oil Systems

Foamability and foam stability of diglycerol fatty acid esters (designated as Qn‐D, where, n represents the carbon number in the alkyl chain of the amphiphile) were studied in different nonaqueous solvents, namely, liquid paraffin (LP70), squalane, squalene, and glycerol tris (2‐ethylhexanoic) ester (TIO) at 25°C. Five per cent by weight of diglycerol monomyristate (Q14‐D) in LP 70 gave super‐stable foam among all oils; not ruptured for more than 12 hours. Q14‐D/squalene also formed very stable foam, whereas there was no foam in a Q14‐D/squalane system. Diglycerol monolaurate (Q12‐D) in LP 70, squalene and squalane gave foams, which coarsened quickly, leading to the progressive destruction of the foam within few minutes. The above systems are essentially dispersions in which surfactant solid or liquid crystal is finely divided. After phase separation took place or the surfactant was precipitated at the bottom of vial, no foaming was observed from the supernatant phase, which is almost pure solvent. Hence, the stability of the foams was caused by the dispersed solid or liquid crystal. In nonfoaming and unstable foam systems, surfactant solid and/or liquid crystal coagulated, precipitated very fast and did not stabilize foams. When particle size (∼20 µm) of solid and liquid crystal was small enough, super‐stable foam was produced in systems like in Q14‐D/LP 70. Judging from the SAXS and foaming tests, it is concluded that surfactant solid (Lβ or α‐gel phase) mainly was responsible for the super‐stable nonaqueous foams in these systems instead of lamellar liquid crystalline phase.

Synthesis and physico-chemical characterization of gold nanoparticles softly coated by AOT

Size-controlled gold nanoparticles/surfactant stable systems were prepared by the combined action of the solvated metal atom dispersion (SMAD) technique and confinement in anhydrous sodium bis(2-ethylhexyl)sulfosuccinate (AOT) micellar solution. From liquid samples, by evaporation of the organic solvent, solid gold nanoparticle–surfactant liquid crystals composites were obtained. Sample characterization was performed by X-ray diffraction (SAXS and WAXS), XPS spectroscopy and UV–vis–NIR spectroscopy. All experimental data consistently revealed the coexistence of two gold nanoparticle size populations: bigger nanoparticles (size 20–50 Å) and smaller ones (size of few Å). The two differently-sized gold nanoparticles can be separated by resuspending the gold/surfactant nanocomposite in n-heptane. This operation causes the slow selective precipitation of the bigger nanoparticles softly coated by surfactant leaving, in the surnatant, only the smaller Au nanoparticles. The latter were found to be entrapped in the core of AOT reversed micelles and stabilised by the surfactant adsorption on their surface. Such nanoparticles, as shown by SAXS data, slowly rearrange to a narrower size distribution giving a surnatant containing stable and finely size-controlled gold nanoparticles.

Structural Evolution during the Synthesis of Mesoporous Silica in Fatty Acid/Aminoalkoxysilane/Water Systems

We report on the phase behavior and structural evolution during the early stages of silica templating using surfactant liquid crystals in aminoalkoxysilane/lauric acid/water systems. Specific aminoalkoxysilanes are used so that hydrolysis and condensation reactions are slow enough to follow the changes in the early stages of mesoporous silica formation without the need for very sophisticated techniques. A lyotropic lamellar phase that swells with water is present in the early stages of the system and develops into kinetically correlated siliceous phases with preservation of morphology. Moreover, lyotropic and siliceous phases coexist at a certain time. Hydrolysis and condensation of alkoxysilane groups cause microstructural changes in the lyotropic lamellar phase, as monitored by in situ small-angle X-ray scattering and infrared spectroscopy measurements. Although the changes in the initial lamellar phase depend on the nature of the alkoxysilane groups, the final siliceous phases show similar correlation ...

Control of Pore Sizes in Mesoporous Silica Templated by Liquid Crystals in Block Copolymer−Cosurfactant−Water Systems

Colloidal silica has been polymerized in the aqueous domain of lyotropic liquid crystal phases in ternary surfactant (Pluronic F127 or P123)−cosurfactant (butanol, pentanol, or hexanol)−water systems to create optically transparent mesostructured surfactant−cosurfactant−silica monoliths. The use of ternary systems enriches phase diagrams of aqueous surfactant systems, which in turn introduces more flexibility and diversity into the designed synthesis of mesoporous materials. Lyotropic surfactant liquid crystal phases are preserved throughout the inorganic polymerization and gelation processes and directly template the formation of inorganic mesophases. The cosurfactant chain length and the cosurfactant/surfactant mass ratio have been used to control the pore size. The large shrinkage of mesopores during calcination can be reduced with hydrothermal treatment prior to calcination. Highly ordered mesoporous silica samples with identical pore sizes, but very different wall thickness, can be prepared. The removal of surfactants and cosurfactants gives periodic hexagonal mesoporous silica with excellent thermal and hydrothermal stability.

Characterization of surfactant liquid crystal phases suitable for molecular alignment and measurement of dipolar couplings.

Media employed for imparting partial alignment onto solute molecules have recently attracted considerable attention, since they permit the measurement of NMR parameters for solute biomolecules commonly associated with solid state NMR. Here we characterize a medium which is based on a quasi-ternary surfactant system comprising cetylpyridinium bromide/hexanol/sodium bromide. We demonstrate that dilute solutions of this system can exist in liquid crystalline phases which orient in the magnetic field and allow the measurement of residual dipolar couplings under a variety of conditions. The present system is extremely versatile and robust, tolerating different buffer conditions, temperature ranges and concentrations.

Magnetic-Field-Induced Orientational Ordering of Alkaline Lyotropic Silicate−Surfactant Liquid Crystals

Macroscopically oriented silicate−surfactant liquid crystals are produced by slow cooling of lamellar and hexagonal mesophases through their isotropic−anisotropic phase transition in an 11.7 T magn...

Ceramics from templated oxide gels

Porous ceramic oxides are important in a wide area of applications and can be produced using sol-gel processes. In the past year important developments have been made in the synthesis of gel structures involving the self-assembly and co-operative organization of inorganic and organic colloidal species in aqueous media. Such processes, which frequently involve interactions between inorganic oligomers and surfactant liquid crystal phases, can lead to microporous and mesoporous oxides with a highly uniform structure. Understanding of the mechanisms of formation of these ‘templated’ structures has progressed through the application of a range of advanced physicochemical techniques.

Lyotropic Liquid Crystals and the Structural Lipids of the Stratum Corneum

Lipids were extracted from human stratum corneum and the remaining corneocytes were re aggregated with different lyotropic liquid crystals. Water transport through the reaggregated stratum corneum was determined using a diffusion chamber according to Smith and Blank. The permeability constant for the reaggregated stratum corneum with natural lipids was 25-40% lower than that with the surfactant liquid crystals, but there was no significant difference between different liquid crystals.

Structure and water—oil emulsifying properties of asphaltenes

Alphaltenes were selected on the basis of their capacity to form water—oil emulsions. They were characterized by electron microscopy, surface group analysis, g.p.c. and low-angle X-ray scattering. It appears that the high stability of water-oil emulsions is related to the ‘structuring’ capacity of asphaltenes at the water-oil interface. Some asphaltenes are able to form regularly stacked layers, resembling the behaviour of surfactant liquid crystals.