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. 相似文献
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. 相似文献
The pseudoternary phase behavior of the water/sucrose laurate/ethoxylated mono-di-glyceride/R (+)-limonene systems was investigated for different surfactants mixing ratios (w/w) at 25 °C. The microemulsion boundaries were determined and the surfactants content at the interface of water- R (+)-limonene was estimated. For surfactants mixing ratio (w/w) equals unity, the area of the one phase microemulsion region reaches its maximum. The system with the maximum microemulsion area was investigated using electrical conductivity, dynamic viscosity, small angle X-ray scattering, and nuclear magnetic resonance. Electrical conductivity increases as the water volume fraction increases and a percolation threshold was observed. Dynamic Viscosity varies as function of the water volume fraction in a non-monotonic way giving two-peaked plot. The characteristics of the domain size of the microemulsions called periodicity measured by small angle X-ray scattering increases with the increase in the water volume fraction. The correlation length of the domain size reaches a maximum when plotted against the water volume fraction in the microemulsions. Relative diffusion coefficients of water increase and those of oil decrease with increasing the water volume fractions in the microemulsions indicating structural transitions. 相似文献
Colloidal nanodispersion of lead sulfide has been prepared in the aqueous compartments of water/AOT/n-heptane. Compartmentalization has prevented growth and coagulation of particles in the dispersion. The uv–vis and fluorescence spectral measurements of the colloidal PbS dispersion were taken. Particle size has been determined by laser light scattering, transmission electron microscopy and absorption spectroscopy. The effects of temperature, ω (water/AOT mole ratio), [AOT], and [PbS] on the particle size have been examined. The nanodispersed particles in microemulsion capped with thiophenol and dodecanethiol were isolated and characterized by the TEM and FTIR methods. 相似文献
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%. 相似文献
Colloidal nanodispersion of lead sulfide has been prepared in the aqueous compartments of water/AOT/n-heptane. Compartmentalization has prevented growth and coagulation of particles in the dispersion. The uv–vis and fluorescence spectral measurements of the colloidal PbS dispersion were taken. Particle size has been determined by laser light scattering, transmission electron microscopy and absorption spectroscopy. The effects of temperature, ω (water/AOT mole ratio), [AOT], and [PbS] on the particle size have been examined. The nanodispersed particles in microemulsion capped with thiophenol and dodecanethiol were isolated and characterized by the TEM and FTIR methods.This revised version was published online in August 2005 with a corrected issue number. 相似文献
In a reverse microemulsion consisting of water, oil (octane), an anionic surfactant [aerosol OT (AOT)], and the reactants of the oscillating Belousov-Zhabotinsky (BZ) reaction, a variety of complex spatiotemporal patterns appear. These include traveling and standing waves, spirals that move either toward or away from their centers, spatiotemporal chaos, Turing patterns, segmented waves, and localized structures, both stationary and oscillatory. The system consists of nanometer-sized droplets of water containing the BZ reactants surrounded by a monolayer of AOT, swimming in a sea of oil, through which nonpolar BZ intermediates can diffuse rapidly. We present experimental and computational results on this fascinating system and comment on possible future directions for research. 相似文献
Dispersions of zinc chromate (ZnCrO4) were prepared in H2O/AOT (sodium bis(2-ethylhexyl sulfosuccinate))/n-heptane water-in-oil (W/O) microemulsion medium with various water pool sizes and precursor concentration both without and with sonication. The formation of ZnCrO4 in the microemulsion was verified by XRD and FTIR measurements. The absorbance of the dispersions formed in different water pool sizes was studied. Their dimension in the microemulsion medium was determined by the dynamic light scattering method. Enthalpy of formation of ZnCrO4 in W/O microemulsion medium was measured by isothermal titration calorimetry (ITC). The dimension and morphology of the formed ZnCrO4 colloidal particles examined by transmission electron microscopy (TEM) were strongly dependent on the water pool size, precursor concentration and sonication. 相似文献
Summary The structure of water in bis(2-ethylhexyl)sodium sulfosuccinate (AOT) micelles has been studied as a function of the [H2O]/[AOT] ratio (W) by using the absorption IR due to O−H stretching modes in the 3800–3000 cm−1 range. Three systems have been studied: water/AOT/carbon tetrachloride, water/AOT/n-heptane and water/AOT iso-octane. Experimental spectra are presented and discussed for the O−H stretching region both of
H2O and isotopically diluted HDO molecules in D2O. We have restricted ourselves to the region of small amounts of water (0<W<20) where the properties of the systems change strongly with the water content. The results show that IR spectra can be expressed
as sum of contributions from interfacial and bulk-like water. The fraction of water in the two “regions” within the water
pool was evaluated as a function ofW. From the data a continuous variation appears in the water properties inside micellar cores rather than a two-steps hydration
mechanism. The solubilization of water is described in terms of hydration of the AOT head group and Na+ counterions. The maximum hydration number of AOT was found to be 3.5. The same behaviour has been observed in the three solvents
studied. 相似文献
We first introduce the percolation problems associated with the graph theoretical concepts of (k,l)-sparsity, and make contact with the physical concepts of ordinary and rigidity percolation. We then devise a renormalization
transformation for (k,l)-percolation problems, and investigate its domain of validity. In particular, we show that it allows an exact solution of
(k,l)-percolation problems on hierarchical graphs, for k≤l<2k. We introduce and solve by renormalization such a model, which has the interesting feature of showing both ordinary percolation
and rigidity percolation phase transitions, depending on the values of the parameters. 相似文献
This paper reports that Nd2O3 nanoparticles modified by
AOT(sodium bis(2-ethylhexyl) sulfosuccinate) were prepared using
microemulsion method in the system of water and
propanol/AOT/toluene. Transmission electron microscopy shows that
the Nd2O3 nanoparticles take the shape of sphere with
18\,nm and 31nm with different preparation. The organic sol of
Nd2O3 nanoparticles is very stable at room temperature.
X-ray diffraction results show that the product has hexagonal phase
structure. Two ultraviolet emission band at 344\,nm and 361\,nm
corresponding to the transition of 4D3/2→4I9/2 and 2P3/2→4I112 or 4D3/2
→4I13/2 were observed. 相似文献
We performed small-angle neutron scattering and neutron spin echo experiments on a ternary microemulsion composed of ionic surfactant AOT, water, and decane. Thermal fluctuations of monolayers have been investigated as a function of temperature and pressure. The amphiphilic monolayers become more flexible with increasing temperature and more rigid with increasing pressure. These results are consistent with the microscopic picture that the head-head repulsion of the AOT molecules is enhanced at high temperature while an attractive interaction between the hydrophobic tails of the AOT molecules increases at high pressure. 相似文献
We have demonstrated a unique approach to alter the aqueous pool size of an AOT/n-heptane/water reverse micellar system. A positively charged dye Rhodamine B (RhB) and negatively charged Rose Bengal (RB) were incorporated in the reverse micellar pool to investigate the effect of electrostatic interactions and stacking effects among the dye molecules on the AOT/n-heptane/water interface. Dynamic light scattering revealed increase in reverse micellar pool size in presence of positively charged dye aggregates at the oil–water interface. However, less expansion was observed in presence of negatively charged dye aggregates (RB). This confirms the role of electrostatic interaction in modulating the hydrodynamic radius. A head-to-tail type of stacking of RhB molecules at the interface favors this expansion. The differences in stacking of the two dyes inside the reverse micelles and their torsional mobility indicated the role of the reverse micellar interface and H-bonding ability of the microenvironment on dye aggregation. Conductivity measurements demonstrated a significant drop in percolation temperature of the reverse micellar system in presence of dye aggregates. This confirms the effect of dye aggregation and electrostatic interaction on such expansion. This strategy can be exploited for solubilizing greater amounts and a wider variety of drug molecules in microemulsions.
In this paper, the percolation of (a) linear segments of size k and(b) k-mers of different structures and forms deposited on a square lattice have been studied. In the latter case, site and bond percolation have been examined. The analysis of results obtained by using finite size scaling theory is performed in order to test the universality of the problem by determining the numerical values of the critical exponents of the phase transition occurring in the system. It is also determined that the percolation threshold exhibits a exponentially decreasing function when it is plotted as a function of the k-mer size. The characteristic parameters of that function are dependent not only on the form and structure of the k-mers but also on the properties of the lattice where they are deposited.Received: 3 September 2003, Published online: 23 December 2003PACS:
64.60.Ak Renormalization-group, fractal, and percolation studies of phase transitions - 68.35.Rh Phase transitions and critical phenomena - 68.35.Fx Diffusion; interface formation 相似文献
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 相似文献
An increased knowledge of polymer crystallization kinetics and its effect on the crystalline structure is of particular importance at high cooling rates. The aims of this study were to explore the range of utility and complementarity of various methods (densitometry, microscopy, wide-angle x-ray diffraction [WAXD], and small-angle light scattering [SALS]) on the characterization of the crystalline structure of a high purity isotactic polypropylene (PP) in a wider cooling range than previously obtainable and to identify characteristic ranges of the structure as a function of cooling rate. High cooling rates, ranging to nearly 1000°C/sec, were obtained using a special quench device. The transition between truncated and isolated spherulites at 10°C/sec and the transition range between a pronounced α-monoclinic and a mainly mesomorphic phase were identified. The sizes of spherulites (ranging from partly truncated spherulites to a mesomorphic phase with no spherulites) were characterized by polarized optical microscopy and SALS. The influence of experimental conditions, such as beam diameter and sample thickness, on the SALS pattern was also investigated. 相似文献
Small angle neutron scattering (SANS) experiments have been carried out on the micellar solutions containing mixtures of a
hydrophobic triblock copolymer (L121, EO5PO68EO5) and a hydrophobic anionic surfactant (AOT, sodium bis(2-ethylhexyl)sulphosuccinate) in water with varying ratio (R) of AOT to L121 for R = 0.15, 0.2, 0.3, 0.5 and 0.6. It is known that either L121 or AOT alone forms vesicles in water, but in the mixture with
appropriate ratio of the two components a thermodynamically stable, isotropic solution of apparently small micelle-like aggregates
is formed. We find that these micelles are prolate ellipsoidal.
相似文献
Recently, the percolation transition has been characterized on interacting networks both in presence of interdependent interactions and in presence of antagonistic interactions. Here we characterize the phase diagram of the percolation transition in two Poisson interdependent networks with a percentage q of antagonistic nodes. We show that this system can present a bistability of the steady state solutions, and both discontinuous and continuous phase transitions. In particular, we observe a bistability of the solutions in some regions of the phase space also for a small fraction of antagonistic interactions 0<q<0.4. Moreover, we show that a fraction q>qc=2/3 of antagonistic interactions is necessary to strongly reduce the region in phase-space in which both networks are percolating. This last result suggests that interdependent networks are robust to the presence of antagonistic interactions. Our approach can be extended to multiple networks, and to complex boolean rules for regulating the percolation phase transition. 相似文献