Optical activity of microemulsion induced by electric field and its tunable behaviors

It has been shown that optical activity can occur in microemulsion under external electric field and rotation angle can also be tuned by the electric field. A set of microemulsions (water/Span80/transformer oil) with different water concentration were prepared and their optical activity was measured with the changes of applied electric field and θ, the angle between the electric vector of the incident linearly polarized light and the external electric field, using an automatic polarimeter. The experiments indicate that when none of the external electric field, water concentration and θ are zero, there is optical activity in microemulsions. For a given concentration, rotation angle ψ increases with electric field, and it firstly increases, passes through a maximum at C = C0,then monotonically decreases as C increases when electric field keeps constant. The relationship between the rotation angle and θ is also obtained. It is thought that the electric field-induced destroy of spatial symmetry of microemulsion is responsible for the optical activity of microemulsion.     

Small-angle light scattering studies of dense AOT-water-decane microemulsions

Summary We have performed extensive studies of a three-component microemulsion system composed of AOT-water-decane (AOT=sodium-bis-ethylhexyl-sulfosuccinate is an ionic surfactant) using small-angle light scattering (SALS). The small-angle scattering intensities are measured in the angular interval 0.001–0.1 radians, corresponding to a Bragg wave number range of 0.14 μm⁻¹<Q<<1.4 μm⁻¹. The measurements were made by changing temperature and volume fraction ϕ of the dispersed phase (water + AOT) in the range 0.05<ϕ<0.75. All samples have a fixed water-to-AOT molar ratio,w=[water]/[AOT]=40.8, in order to keep the same average droplet size in the stable one-phase region. With the SALS technique, we have been able to observe all the phase boundaries of a very complex phase diagram with a percolation line and many structural organizations within it. We observe at the percolation transition threshold, a scaling behavior of the intensity data. This behavior is a consequence of a clustering among microemulsion droplets near the percolation threshold. In addition, we describe in detail a structural transition from a droplet microemulsion to a bicontinuous one as suggested by a recent small-angle neutron scattering experiment. The loci of this transition are located several degrees above the percolation temperatures and are coincident with the maxima previously observed in shear viscosity. From the data analysis, we show that both the percolation phenomenon and this novel structural transition are derived from a large-scale aggregation between microemulsion droplets.     

Structure/Property Relationships for Poly(Vinylidene Fluoride)/Doped Polyaniline Blends

Poly(vinylidene fluoride) (PVDF) and its blends with polyaniline (PANI) doped with dodecylbenzene sulfonic acid (DBSA) were characterized by electrical conductivity, differential scanning calorimetry (DSC) and X‐ray scattering techniques.

The onset of an infinite cluster (InC) of conducting, highly anisometric PANI/DBSA particles in PVDF/(PANI/DBSA) blends was observed at the percolation threshold as low as w*≈3.5 wt.%. The small angle X‐ray scattering (SAXS) data confirmed the expected spatial organization of PANI/DBSA needles into fractal‐like structures above w*. A slight decrease of both the DSC and the wide‐angle X‐ray scattering (WAXS) degrees of crystallinity of PVDF with the PANI/DBSA mass content w was explained by strong interactions at the PVDF/(PANI/DBSA) interface resulting in the loss of crystallizability of a fraction of sterically immobilized chains of PVDF in boundary layers around PANI/DBSA particles. The available data suggest that the conductive paths within InC of PANI/DBSA in PVDF/(PANI/DBSA) blends were formed primarily by the end‐to‐end contacts of PANI/DBSA fibrils.     

Small-angle light scattering in dense microemulsions,transition from droplet to bicontinuous phase

Summary We have performed extensive small-angle light scattering (SALS) measurements on a three-component microemulsion (AOT/decane/water) as a function of the dispersed phase concentration and the temperature. All samples have a water/AOT molar fractionw=40.8. Such a system presents a very complex phase diagram with many structural configurations. With the SALS technique, we have been able to observe all the phase separation lines. In particular we give details on the system structure on the percolation phenomenon and on the bicontinuous phase recently observed. In particular we show that the percolation is driven by a long-scale aggregation between microemulsion droplets. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Liquid/liquid metal extraction: Phase diagram topology resulting from molecular interactions between extractant, ion, oil and water

We consider the class of surfactants called ??extractants?? since they specifically interact with some cations and are used in liquid-liquid separation processes. We review here features of water-poor reverse micelles in water/oil/ extractant systems as determined by combined structural studies including small angle scattering techniques on absolute scale. Origins of instabilities, liquid-liquid separation as well as emulsification failure are detected. Phase diagrams contain the same multi-phase domains as classical microemulsions, but special unusual features appear due to the high spontaneous curvature directed towards the polar cores of aggregates as well as rigidity of the film made by extracting molecules.     

Investigation of W/O microemulsion droplets by contrast variation light scattering

Dynamic and static light scattering experiments have been performed at various molar ratios (γ) of water to AOT and temperatures on water-in-oil (W/O) microemulsions dispersed in n-heptane, n-octane, and n-nonane. Size and shape fluctuations of microemulsion droplets are determined with very high precision because polydispersity influences the characteristic features of scattering data as well as the hydrodynamic radius withγ. Self-consistent interpretation of dynamic and static light scattering data using optical properties and packing consideration on the basis of the layered sphere model are obtained. The estimated extent of polydispersity index of 17% is found, whereas the polydispersity is independent of the alkane types. The geometrical parameters, e.g., hydrodynamic radius, area per head group of the surfactant molecule and thickness of the surfactant layer of microemulsion droplets are also estimated and compared in three different n-alkane types. The best interpretation of the temperature dependence of data has shown a transition from spherical droplets to ellipsoid aggregates with increasing temperature. Axial ratio increases with increase of temperature and the longer the alkane the larger is the axial ratio. The parameters describing the polydispersity and shape change are in agreement with theoretical and experimental results found in the literature     

Cluster description of water-in-oil microemulsions near the critical and percolation points

The three-component ionic microemulsion system consisting of AOT/water/decane shows an unusual phase behavior in the vicinity of room temperature. The phase diagram in the temperature-volume fraction (of the dispersed phase) plane exhibits a lower consolute critical point at about 40 degrees centigrades and 10% volume fraction. A percolation line, starting from the vicinity of the critical point, cuts across the plane, extending to high volume fraction side at progressively lower temperatures. In this paper we review the evidence that allows to interpret the phase behavior of our system in terms of interacting spherical droplets. We also investigate the dynamics of droplets, below and approaching the critical point by dynamic light scattering. The first cumulant and time evolution of the droplet density correlation function can be quantitatively calculated by assuming the existence of polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena observed in an extensive set of measurements of electrical conductivity and permittivity close to percolation is also reviewed and interpreted through the same cluster-forming mechanism, which reproduces the most relevant features of the frequency-dependent complex dielectric constant of this system. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Preparation of AgBr Nanoparticles in Microemulsions Via Reaction of AgNO<Subscript>3</Subscript> with CTAB Counterion

Nanoparticles of AgBr were prepared by precipitating AgBr in the water pools of microemulsions consisting of CTAB, n-butanol, isooctane and water. An aqueous solution of AgNO₃ added to the microemulsion was the source of Ag⁺ ions. The formation of AgBr nanoparticles in microemulsions through direct reaction with the surfactant counterion is a novel approach aimed at decreasing the role of intermicellar nucleation on nanoparticle formation for rapid reactions. The availability of the surfactant counterion in every reverse micelle and the rapidity of the reaction with the counterion trigger nucleation within individual reverse micelles. The effect of the following variables on the particle size and size distribution was investigated: the surfactant and cosurfactant concentrations, moles of AgNO₃ added, and water to surfactant mole ratio, R. High concentration of the surfactant or cosurfactant, or high water content of the microemulsion favored intermicellar nucleation and resulted in the formation of large particles with broad size distribution, while high amounts of AgNO₃ favored nucleation within individual micelles and resulted in small nanoparticles with narrow size distribution. A blue shift in the UV absorption threshold corresponding to a decrease in the particle size was generally observed. Notably, the variation of the absorption peak size with the nanoparticle size was opposite to those reported by us in previous studies using different surfactants.     

Characterization of nanoparticles of lidocaine in w/o micro emulsions using small-angle neutron scattering and dynamic light scattering

Microemulsions (MEs) are of special interest because a variety of reactants can be introduced into the nanometer-sized aqueous domains, leading to materials with controlled size and shape [1,2]. In the past few years, significant research has been conducted in the reverse ME-mediated synthesis of organic nanoparticles [3,4]. In this study, a w/o ME medium was employed for the synthesis of lidocaine by direct precipitation in w/o microemulsion systems: water/isopropylpalmitat/Tween80/Span80. The particle size as well as the location of nanoparticles in the ME droplet were characterized by means of dynamic light scattering (DLS) and small angle neutron scattering (SANS). It is observed that lidocaine precipitated in the aqueous cores because of its insolubility in water. Hydrodynamic radius and gyration radius of microemulsion droplets were estimated as ∼15 nm and ∼4.50 nm from DLS and SANS respectively. Furthermore, different size parameters obtained by DLS and SANS experiments were compared     

聚氨酯离聚体微畴体积的研究

本文用聚氨酯离聚体材料作X射线小角度散射实验,同时还作了正电子湮没及比重法测量材料密度的辅助实验,以研究聚氨酯离聚体微畴体积随金属离子价改变。实验结果表明,随着金属离子价数的增加,反离子半径增大,微畴的体积增大,致使材料的密度增大,自由体积相应减小。 关键词：     

Effect of composition on the conductivity of CTAB-butanol-octane-nitrate salts (Al(NO3)3 + Zn(NO3)2) microemulsions and on the surface and textural properties of resulting spinels ZnAl2O4

The conductivity σ of a microemulsion series consisting of CTAB + butanol + octane, in which a solution of Al(NO₃)₃ 0.8 M + Zn(NO₃)₂ 0.4 M was gradually added, was studied at room temperature as a function of its composition φ. The addition of nitrate salts solution took place in four different ratios of (butanol + CTAB):octane = 0.2, 0.4, 0.6 and 0.8. Initially, all those four systems are (water in oil, w/o) microemulsions and the gradual addition of the solution of the nitrate salts transforms them to bicontinuous ones. The conductivity increases gradually, but with different rate in each case, and the corresponding critical exponents at the percolation threshold were determined from the curves σ = f(φ). Next at three different compositions of microemulsions, corresponding to ratios (butanol + CTAB):octane = 0.4, 0.6 and 0.8 and ratio of the nitrate salts solution x ≈ 0.25, spinels ZnAl₂O₄ were isolated/prepared. XRD, SEM and N₂ adsorption-desorption measurements were used to determine the structure and texture of those solids. From those measurements the surface area (S_p), the pore volume (V_p), the size of crystallites and the average pore connectivity (c) were found. Those properties showed considerable variation and dependence on the composition of the original microemulsions employed in the preparation, a fact indicating that the structure and texture of the obtained solids can be manipulated at will via the composition of microemulsion used.     

Percolation phenomenon of calcium bis(2-ethylhexyl) sulfosuccinate water-in-oil microemulsions by conductivity and dielectric spectroscopy measurements

The sodium counterion (Na+) of the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant was exchanged with calcium Ca2+ to investigate the counterion charge effect on the structure of water in normal decane microemulsions. Ohmic conductivity and dielectric permittivity measurements were performed on samples at constant water to surfactant mole ratio [water]/[Ca(AOT)(2)]=26.6. Increasing the volume fraction of the dispersed phase phi, a percolation phenomenon was observed at the constant temperature of 25 degrees C. The percolation threshold was found at phi approximately 15% by Ohmic conductivity and static dielectric permittivity studied as a function of phi, and by the frequency dependence of the complex permittivity. Critical exponents typical of the static percolation mechanism (formation of bicontinuous microemulsions) were found below and above threshold. The comparison of these results obtained for the two different counterions, Ca2+ and Na+, in AOT surfactant water in normal decane microemulsions allows detection of an important difference. The percolation below threshold is dynamic for the sodium-based microemulsions, accounting for the formation of clusters of droplets, whereas calcium-based microemulsions show a static percolation. For this system, the coalescence of droplets begins to occur below threshold at phi approximately 12%.     

Characterisation of colloidal drug delivery systems from the naked eye to Cryo-FESEM

Poly(ethylcyanoacrylate) nanoparticles prepared by interfacial polymerisation on the basis of microemulsions were prepared in this study and both colloidal systems, nanoparticles and microemulsions, were analysed by visual observation and several microscopic techniques. Phase boundaries for the microemulsions of the two pseudoternary systems ethyloleate, polyoxyethylene 20 sorbitan mono-oleate/sorbitan monolaurate and water with and without butanol as a cosurfactant were determined by visual observation of the samples. Microemulsions containing liquid crystals were determined by polarisation light microscopy. Using freeze-fracture transmission electron microscopy and Cryo-field emission scanning electron microscopy the type of microemulsion (w/o droplet, bicontinuous, solution) was characterised. Nanoparticles prepared from the different types of microemulsion were additionally observed by conventional scanning electron microscopy. The size of the nanoparticles obtained from electron microscopy was in good agreement with particle sizing techniques (photon correlation spectroscopy) from earlier studies and no morphological differences could be observed in particles prepared from the different types of microemulsions. Cryo-field emission scanning electron microscopy proved to be a most valuable technique in the visualisation of the colloidal systems as samples could be observed close to their natural state.     

Single-shot two-dimensional measurement of nanoparticles in turbulent jet-diffusion flames using phase-selective laser-induced breakdown spectroscopy

In this work, we demonstrate a single-shot two-dimensional measurement of vanadic oxide (V₂O₅) nanoparticles in a turbulent jet-diffusion flame based on phase-selective laser-induced breakdown spectroscopy (PS-LIBS). By collecting the atomic spectra of vanadium near 439?nm from nano-sized plasmas within the ～30?ns lifetime, particle information can be revealed without interference from elastic scattering or Bremsstrahlung emissions. As the laser intensity increases, the signal intensity first increases and then saturates when the laser intensity reaches 0.5 GW/cm². In the saturation regime, a proportional correlation is established between the signal intensity and the particle volume fraction. Based on the parametric study in the laminar condition, we image the instantaneous distribution of particle volume fraction in the turbulent condition using single-shot PS-LIBS measurements. The snapshots show that vanadic oxide nanoparticles concentrate near the diffusion flame surface, which may be caused by the rapid formation of particles on the oxidizer/precursor side and quick dilution across the reaction layer. The Proper Orthogonal Decomposition (POD) analysis further indicates that the fluctuations of the particle volume fraction originate from the unsteady flame surface at the upstream positions and large-scale mixing at the downstream positions. The single-shot PS-LIBS measurement shows promising potential for resolving complex processes of particle formation in turbulent flame synthesis.     

Thermal conductivity of crystalline fullerite C60 in the simple cubic phase

The behavior of the thermal conductivity k(T) of bulk faceted fullerite C₆₀ crystals is investigated at temperatures T=8–220 K. The samples are prepared by the gas-transport method from pure C₆₀, containing less than 0.01% impurities. It is found that as the temperature decreases, the thermal conductivity of the crystal increases, reaches a maximum at T=15–20 K, and drops by a factor of ∼2, proportional to the change in the specific heat, on cooling to 8 K. The effective phonon mean free path λ _p, estimated from the thermal conductivity and known from the published values of the specific heat of fullerite, is comparable to the lattice constant of the crystal λ _p∼d=1.4 nm at temperatures T>200 K and reaches values λ_p∼50d at T<15 K, i.e., the maximum phonon ranges are limited by scattering on defects in the volume of the sample in the simple cubic phase. In the range T=25−75 K the observed temperature dependence k(T) can be described by the expression k(T)∼exp(Θ/bT), characteristic for the behavior of the thermal conductivity of perfect nonconducting crystals at temperatures below the Debye temperature Θ (Θ=80 K in fullerite), where umklapp phonon-phonon scattering processes predominate in the volume of the sample. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 651–656 (25 April 1997)     

Influence of Mixing Technique on Microstructure and Impact Properties of Isotactic Polypropylene/ Poly(Cis-Butadiene) Rubber Blends

Isotactic polypropylene/poly(cis-butadiene) rubber (iPP/PcBR vol%: 80/20) blends were prepared by melt mixing with various mixing rotation speeds. The effect of mixing technique on microstructure and impact property of blends was studied. Phase structure of the blends was analyzed by scanning electron microscopy (SEM). All of the blends had a heterogeneous morphology. The spherical particles attributed to the PcBR-rich phase were uniformly dispersed in the continuous iPP matrix. With increase of the mixing rotation speed, the dispersed phase particle's diameter distribution became broader and the average diameter of the separated particles increased. The spherulitic morphology of the blends was observed by small angle light scattering (SALS). Higher mixing rotation speed led to a more imperfect spherulitic morphology and smaller spherulites. Crystalline structure of the blends was measured by wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). The introduction of 20 vol% PcBR induced the formation of iPPβ crystals. Higher rotation speed led to a decrease in microcrystal dimensions. However, the addition of PcBR and the increase of mixing rotation speed did not affect the interplanar distance. The long period values were the same within experimental error as PcBR was added or the mixing rotation speed quickened. The normalized relative degree of crystallinity of the blends slightly increased under lower rotation speeds (30 and 45 rpm) and decreased under higher rotation speeds. The notched Izod impact strength of the blends was enhanced as a result of the increase of mixing rotation speed.     

TRANSPORT PROPERTIES OF μc-Si:H FILMS PREPARED BY VERY HIGH HYDROGEN-DILUTED SILANE PLASMA

Highly hydrogen-diluted silane plasma is used to fabricate microcrystalline silicon films in a plasma-enhanced chemical vapour deposition system. X-ray diffraction and micro-Raman scattering spectroscopy are utilized to characterize their microstructure properties. Dark conductivity and drift mobility are measured by the travelling wave method. With the decreasing gas flow ratio of silane-to-hydrogen from 2% to 0.2%, the crystalline volume fraction and the drift mobility increase at room temperature. Meanwhile, the dark conductivity increases initially and then decreases. The relationship between the microstructures and transport properties is discussed.     

Structure Formation from the Oriented Glassy States of Poly(Ethylene Terephthalate)

The ordering process of poly(ethylene terephthalate) (PET) from the oriented glassy states during the isothermal annealing process was investigated using real-time X-ray scattering experiments with synchrotron radiation sources. The X-ray scattering intensity of the 001' reflection, which is a measure of the smectic order with respect to chain alignment, increases with time and then begins to decrease after reaching a maximum. The intensity of the four-point pattern in the small-angle X-ray scattering region, which is a measure of the fraction of a crystal-like structure with a tilted lamellar structure, increases monotonically with time. Hence, the fraction of PET chains with smectic-like order has a maximum during the isothermal process, while that of the crystal-like structure increases monotonically. The kinetics of structure formation from the nematic-like structure to the crystal-like structure by way of the smectic structure will be discussed.     

Thermally-stimulated-depolarization study on the highly viscous isotropic mesophase of w/o microemulsions

Summary Highly viscous, optically isotropic water-in-oil microemulsion samples (dodecane, hexanol, potassium oleate plus water) with water content in the concentration interval 0.68≤C<0.8 (C, mass fraction) were studied by means of the thermally-stimulated-depolarization (TSD) method. Different polarizing temperatures were tested from 293 K down to 188 K. Depending on the polarizing temperature, the intensity of the static electric field was increased from 33 V/cm up to 10 kV/cm. The temperature dependence of the field-induced orientation processes was investigated and the activation energy and the relaxation time of the depolarization processes that were found to follow a first-order relaxation kinetic were evaluated. The temperature domain within which the viscous, isotopic mesophase may exist was also identified. The low-temperature TSD spectra of highly viscous, isotropic microemulsion samples are characterized by a current peak atT=198 K which follows a first-order kinetic and whose maximum current peak intensity is an inverse function of the polarizing temperature. Paper presented at the ?Meeting on Lyotropics and Related Fields?, held in Rende, Cosenza, September 13–18, 1982.     

Fabrication, characterization and measurement of thermal conductivity of Fe3O4 nanofluids

Magnetite Fe₃O₄ nanoparticles were synthesized by a co-precipitation method at different pH values. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronic microscopy. Their magnetic properties were evaluated on a vibrating sample magnetometer. The results show that the shape of the particles is cubic and they are superparamagnetic at room temperature. Magnetic nanofluids were prepared by dispersing the Fe₃O₄ nanoparticles in water as a base fluid in the presence of tetramethyl ammonium hydroxide as a dispersant. The thermal conductivity of the nanofluids was measured as a function of volume fraction and temperature. The results show that the thermal conductivity ratio of the nanofluids increases with increase in temperature and volume fraction. The highest enhancement of thermal conductivity was 11.5% in the nanofluid of 3 vol% of nanoparticles at 40 °C. The experimental results were also compared with the theoretical models.