Generalized Indirect Fourier Transformation Research Articles

Effect of polyols on membrane structures of liposomes: A study using small-angle X-ray scattering data and generalized indirect Fourier transformation

This study aimed to evaluate the membrane structure of distearoylphosphatidylcholine (DSPC) liposomes dispersed in water containing various types of polyols with low molecular weight such as glycerin (Gly), 1,3-butandiol (BG), and propylene glycol (PG). To clarify the detailed membrane structure, generalized indirect Fourier transformation (GIFT) analysis, which provides information about the bilayer spacing, bilayer thickness, number of lamellar layers, and membrane flexibility, was applied to small-angle X-ray scattering (SAXS) data of the present system. The GIFT results showed that the bilayer thickness of the DSPC liposomes followed the order Gly>>BG>PG. In addition, the membrane flexibility estimated by the Caille parameter was in the order Gly>>BG>PG; this result was supported by the gel-liquid crystal phase transition temperature (Tc) obtained by differential scanning calorimetry (DSC). These results, together with the Raman spectra, suggest that BG and PG incorporated into the bilayers of DSPC liposomes result in the formation of an interdigitated lamellar structure.

Small Angle X-ray Scattering and Electron Spin Resonance Spectroscopy Study on Fragrance Infused Cationic Vesicles Modeling Scent-Releasing Fabric Softeners.

Industrially relevant systems for household and personal-care products often involve a large number of components. Such multiple component formulations are indispensable and effective for functionalization of the products, but may simultaneously provide more complex structural features compared to those in ideal systems comprising a smaller number of highly pure substances. Using cryogenic transmission electron microscopy (cryo-TEM), small angle X-ray scattering (SAXS), and electron spin resonance (ESR) spectroscopy, we have investigated effects of fragrance-incorporation into cationic vesicles on their bilayer structures and membrane-membrane interactions. Cationic vesicles were prepared from TEQ surfactant, whose major component was di(alkyl fatty ester) quaternary ammonium methosulfate, and fragrance components, l-menthol, linalool, and d-limonene, were infused into the vesicle membranes to model scent-releasing fabric softeners. The cryo-TEM images confirm formation of multilamellar vesicles (MLVs). Generalized indirect Fourier transformation (GIFT) analysis of the SAXS intensities based on the modified Caillé structure factor model reveals that incorporation of a more hydrophobic fragrance component leads to a more pronounced increase of the surface separation (water layer thickness). Furthermore, the fragrance-infused systems show longer-range order of the bilayer correlations and enhanced undulation fluctuation of the membranes than those in the TEQ alone system. The spin-label ESR results indicate different restricted molecular motions in the TEQ bilayers depending on the labeled position and their marked changes upon addition of the fragrance components, suggesting different mixing schemes and solubilization positions of the fragrance molecules in the TEQ bilayers. The present data have demonstrated how the infused fragrance molecules having different hydrophobicity and molecular architectures into the cationic vesicles affect the membrane structures and the intermembrane interactions, which may provide useful information for precisely controlling a fragrance-releasing property.

In Situ Structural Changes of Biological Macromolecules with BioSAXS

Biological small angle X-ray scattering (BioSAXS) is a nowadays well-established technique to study low resolution structural changes within biological macromolecules in their native environment. In addition, SAXS is a powerful tool for structural characterization and the quantitative analysis of flexible system as a highly complementary method to the high resolution methods of X-ray crystallography and NMR. In general, BioSAXS allows studying three dimensional low resolution structures in different chemical environments under defined conditions (e.g., temperature, pH, dielectric properties, etc.) using not only ab initio methods but also rigid body modeling. Furthermore, the shape (form factor) and interaction potential (structure factor) of the active quaternary protein structure can be assessed using the pair distance distribution function (PDDF) with the use of the generalized indirect Fourier transformation (GIFT). Especially in situ measurements of biological macromolecules have gained a lot of attention in the last decades due to the related structural changes and correlated bioactivity (i.e., native and denatured state).As model substance, Lysozyme was analyzed in terms of its quaternary structural changes upon in situ heat treatment and changes in the dielectric constant of the chemical environment. The validation of the form and structure factor components of the analyzed system allows determining the influence of the changed environmental conditions on the protein structure. The changed chemical environment causes an elongation of the previously globular protein structure. In aqueous environment, Lysozyme is stabilized via electrostatic stabilization. In ethanolic solution, the stabilization mechanism is changed, resulting in a change of structure (e.g., elongation).

Nonionic amphiphile nanoarchitectonics: self-assembly into micelles and lyotropic liquid crystals

Amphiphiles, molecules that possess both hydrophilic and hydrophobic moieties, are architecturally simple molecules that can spontaneously self-assemble into complex hierarchical structures from lower to higher dimensions either in the bulk phase or at an interface. Recent developments in multifunctional nanostructure design using the advanced concept of nanoarchitectonics utilize this simple process of assembly. Amphiphilic self-assemblies involving lipids or proteins mimic the structure of biological systems, thus highlighting the necessity of a fundamental physical understanding of amphiphilic self-assembly towards a realization of the complex mechanisms operating in nature. Herein, we describe self-assembled microstructures of biocompatible and biodegradable tetraglycerol lauryl ether (C12G4) nonionic surfactant in an aqueous solvent system. Temperature-composition analyses of equilibrium phases identified by using small-angle x-ray scattering (SAXS) provide strong evidence of various spontaneously self-assembled mesostructures, such as normal micelles (Wm), hexagonal liquid crystal (H1), and reverse micelles (Om). In contrast to conventional poly(oxyethylene) nonionic surfactants, C12G4 did not exhibit the clouding phenomenon at higher temperatures (phase separation was not observed up to 100 °C), demonstrating the greater thermal stability of the self-assembled mesophases. Generalized indirect Fourier transformation (GIFT) evaluation of the SAXS data confirmed the formation of core–shell–type spherical micelles with a maximum dimension ca. 8.7 nm. The shape and size of the C12G4 micelles remained apparently unchanged over a wide range of concentrations (up to 20%), but intermicellar interactions increased and could be described by the Percus–Yevick (PY) theory (after Carnahan and Starling), which provides a very accurate analytical expression for the osmotic pressure of a monodisperse hard sphere.

A SAXS Study of Aggregation in the Synergistic TBP–HDBP Solvent Extraction System

The macroscopic phase behaviors of a solvent system containing two extractants, tri-n-butyl phosphate (TBP) and di-n-butyl phosphoric acid (HDBP) in n-dodecane, were investigated through use of liquid-liquid extraction and small-angle X-ray scattering (SAXS) experiments. Five organic solutions, each containing a total extractant concentration (TBP + HDBP) of 1 M in varying molar ratios (0, 0.25, 0.5, 0.75, and 1.0 [TBP]:[TBP + HDBP]), were contacted with 0.2 M HNO3 aqueous solutions without and with dysprosium(III) at a concentration of 10(-4) M. An enhancement of the extraction of Dy(3+)--due to effects of synergism arising from the binary combination of extractants--was observed. SAXS data were collected for all solution compositions from 0 to 1 mol-fraction end ratios of TBP after contact with the acidic aqueous solutions both in the absence and presence of Dy as well as for the organic phases before aqueous contact. In the precontacted solutions, no notable changes in the SAXS data were observed upon combining the extractants so that the scattering intensity (I) measured at zero angle (Q = 0 Å(-1))--parameter I(0)--the experimental radius of gyration (R(g)), and the maximum linear extent (MLE) of the extractant aggregates were arithmetic averages of the two end members, 1 M HDBP, on the one hand, and 1 M TBP, on the other. In contrast, after contact with the aqueous phases with and without Dy(3+), a significant reorganization occurs with larger aggregates apparent in the extractant mixtures and smaller in the two end member solutions. In particular, the maximum values of the metrical parameters (I(0), R(g), and MLE) correlate with the apparent optimal synergistic extraction mole ratio of 0.25. The SAXS data were further analyzed using the recently developed generalized indirect Fourier transformation (GIFT) method to provide pair-distance distribution functions with real-space information on aggregate morphology. Before aqueous contact, the organic phases show a systematically varying response from globular-like reverse micelles in the case of 1 M TBP to rod-shaped architectures in the case of 1 M HDBP. After aqueous contact, the aggregate morphologies of the mixed extractant systems are not simple linear combinations of those for the two end members. Rather, they have larger and more elongated structures, showing sharp discontinuities in the metrics of the aggregate entities that are coincident with the synergistic extraction mixture for Dy(3+). The results in this initial study suggest a supramolecular, micellization aspect to synergism that remains underexplored and warrants further investigation, especially as it concerns the contemporary relevance to decades-old process chemistry and practices for high throughput separations systems.

Structure of Nonionic Reverse Micelles in Octylbenzene

We report structure and rheology (flow property) of diglycerol monomyristate (designated as C14G2) reverse micelles in an aromatic solvent octylbenzene. Structural characterization has been made using small-angle x-ray scattering (SAXS), while flow property is studied using rheometry. SAXS data have been evaluated by the generalized indirect Fourier transformation (GIFT) method and geometrical model fittings. We found that, under ambient conditions of temperature and pressure, C14G2 spontaneously self-organize into ellipsoidal prolate-type micelles with maximum core diameter of about 6.5 nm in octylbenzene. Shape and size of the micelles remain essentially unchanged over wide concentrations (3–20%). On the other hand, micellar size decreases with increase in temperature, which is anticipated to be due to an increase in the critical packing parameter (CPP). Since surfactant becomes lipophilic upon heating, micellar curvature becomes more negative at higher temperatures. Steady-shear rheological experiments showed that the present reverse micelles behave as a Newtonian fluids; measured viscosity is independent of the applied shear. Zero-shear viscosity tends to increase with weight fraction of the surfactant, which is assumed to be caused due to an increase in number density of micelles.

Generalized Indirect Fourier Transformation as a Valuable Tool for the Structural Characterization of Aqueous Nanocrystalline Cellulose Suspensions by Small Angle X-ray Scattering

Small angle X-ray scattering (SAXS) is employed to characterize the inner structure and shape of aqueous nanocrystalline cellulose suspensions using the generalized indirect Fourier transformation (GIFT). The use of the GIFT approach provides a single fitting procedure for the determination of intra- and interparticle interactions due to a simultaneous treatment of the form factor P(q) and the structure factor S(q). Moreover, GIFT allows for the determination of particle charges and polydispersity indices. As test material, aqueous nanocrystalline cellulose suspensions (aNCS) prepared by the H2SO4 route have been investigated and characterized (SAXS, dynamic light scattering, zeta potential).

Location of Cholesterol in Liposomes by Using Small-angle X-ray Scattering (SAXS) Data and the Generalized Indirect Fourier Transformation (GIFT) Method

We investigated the location of cholesterol (Chol) in liposomes and its interaction with phospholipids using small-angle x-ray scattering (SAXS) data and applying the generalized indirect Fourier transformation (GIFT) method. The GIFT method has been applied to lamellar liquid crystal systems and it gives quantitative data on bilayer thickness, electron density profile, and membrane flexibility (Caillé parameter). When the GIFT method is applied to the SAXS data of dipalmitoylphosphatidylcholine (DPPC) alone (Chol [-]) or a DPPC/Chol = 7/3 mixed system (Chol [+], molar ratio), change in the bilayer thickness was insignificant in both systems. However, the electron density for the Chol (+) system was higher than that for the Chol (-) system at the location of hydrophilic groups of phospholipids, and whereas Caillé parameter value increased with temperature for the Chol (-) system, no significant change with temperature was observed in the Caillé parameter for the Chol (+) system. These results indicated that Chol is located in the vicinity of the hydrophilic group of the phospholipids and constricts the packing of the acyl chain of phospholipids in the bilayer.

Formation and Cleansing Performance of Bicontinuous Microemulsions in Water/Poly (oxyethylene) Alkyl Ether/Ester-Type Oil Systems

Phase behaviors in water/poly(oxyethylene) dodecyl ether (C₁₂EO(n), n = 4, 6, 8)/cetyl isooctanoate (CIO) systems were studied. In the C₁₂EO₆ and C₁₂EO₈ systems, self-assembled structures with positive curvatures, such as O/W microemulsions, and micellar cubic and hexagonal phases, were observed. A wider region of a lamellar liquid-crystalline phase, which included a narrow microemulsion region joined by a miscibility gap, was observed in the C₁₂EO₄ system. The structure of the microemulsion phase in the C₁₂EO₄ system was characterized by pulsed-field-gradient NMR (PFG-NMR) and small angle X-ray scattering (SAXS) techniques. PFG-NMR measurements indicated that the structure of the microemulsion was bicontinuous; both water and oil phases were continuous within the microemulsion. Pair-distance distribution function, p (r), and structure factors obtained by Generalized Indirect Fourier Transformation (GIFT) analysis of the SAXS data showed that the microemulsion domain sizes decreased with an increase in the oil content. The structure of the bicontinuous microemulsion was consistent with the results of a detergency test, in which the microemulsion samples were applied to lipstick dirt on an artificial skin plate. Detergency was observed to be better for the microemulsion at lower oil contents because of the larger oil domain size at these low concentrations.

Mesoscopic Aspects of Phase Transitions in a Solvent Extraction System

In liquid-liquid extraction, organic phase splitting arises when high concentrations of polar solutes (acids/metal ions) are extracted. Herein, we investigate the mesoscopic roots that underpin phase splitting in alkane phases containing mixed amphiphiles, of contemporary interest in solvent extraction separation systems, by extracting various oxoacids. The oxoacids exhibited individual macroscopic (extractive and physical) behaviors, inducing phase splitting into heavy and light domains under markedly different conditions. Using small-angle X-ray scattering (SAXS) data analyzed using the generalized indirect Fourier transform (GIFT) method, we showed that, in all cases, acid extraction drove the self-assembly of reverse micelles into rods. These grew with increased acid extraction until reaching a critical length of 20 nm, at which point interactions produced interconnected cylinders or lamellar sheets that prelude phase splitting into heavy and light domains. In all cases, the heavy phase contained the same surfactant ratio-TBP (tri-n-butyl phosphate) and CMPO (octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide)-even though the concentrations of acid, water, and amphiphiles were markedly different. The remarkable similarities in structure and amphiphile stoichiometries underpinning phase splitting across the macroscopically different acid extraction series allude to the mesoscopic roots of organic phase behavior in solvent extraction. Our studies show that the structures underpinning phase splitting in solvent extraction systems are more complex than previously thought and are reminiscent of phase transitions in soft matter.

Characterization of nonionic surfactant micellar structures in organic solvents by small angle X-ray scattering (SAXS)

The micellar structure behavior of nonionic surfactants in nonpolar solvents has attracted great interest in the last years because of its application in the solubilization of several substances, material synthesis and stabilizers of insoluble reactive species in nonpolar solvents. In the present work we report a study on the determination of critical micellar concentration (CMC) and characterization of reverse micelles formed by a nonylphenolpolyethoxylated surfactant (Ultranex-50) in organic solvents (octane, decane and dodecane), employing ethylene glycol monobutyl ether as polar additive. In order to determine CMC and to characterize reverse micelle structural behavior under several factors (type of solvent, surfactant concentration, temperature and polar additive molar ratio), use was made of small angle X-ray scattering (SAXS), employing the generalized indirect Fourier transformation (GIFT). Aiming to determine CMC of systems composed of Ultranex-50, ethylene glycol monobutyl ether, and nonpolar solvents, we have acquired data from SAXS with the surfactant concentration varying from 0.005 to 0.2mol/L, with an ethylene glycol monobutyl ether molar ratio of 2:1. First of all, we verified that the formation of aggregates in nonpolar solvents occurred at a surfactant concentration magnitude of 10−2mol/L. From the collected data, we could visualize that for the studied systems the shape of the reverse micelle was predominantly globular. We have observed that micellar size decreases upon heating. Finally, when reducing ethylene glycol monobutyl ether molar ratio, we noticed that the micellar aggregates turned from almost spherical globular structures to less symmetrical ones.

Water Induced Microstructure Transformation of Diglycerol Monolaurate Reverse Micelles in Ethylbenzene

Water induced microstructure transitions of diglycerol monolaurate (C(12)G(2)) reverse micelles in aromatic liquid ethylbenzene have been investigated using small-angle X-ray scattering (SAXS) and rheometry. The SAXS data have been evaluated by generalized indirect Fourier transformation (GIFT) and geometrical model fittings. We found that the C(12)G(2) spontaneously self-assembles into ellipsoidal prolate micelles in ethylbenzene under ambient conditions. The maximum diameter of the micellar core is ca. 5.0 nm. We noted that 5% C(12)G(2)/ethylbenzene solubilize 0.8% water and the water causes micellar growth; micellar size is ~ 3 times bigger than the empty micelles. Rheology data showed that viscosity of 5% C(12)G(2)/ethylbenzene increases with increase in the water concentration sustaining the SAXS results that the viscosity increase is caused due to micellar growth. We found that increase in temperature of the water incorporated system decreases micellar size, which is equivalent to a rod-to-sphere type transition. The water induced microstructure transformations can be explained in terms of critical packing parameter, cpp. Water hydrates hydrophilic headgroup of surfactant so that effective cross-sectional area of surfactant increases. As a result the cpp decreases and micelles grow. On the other hand, increasing temperature promotes interpenetration of solvent and surfactant chain as a result cpp increases due to decrease in the effective cross-sectional area of surfactant. Moreover dehydration may occur and micelles with more curved interface are formed due to increases in the cpp.

Structure of Diglycerol Monomyristate Reverse Micelles in Styrene: A Small-Angle X-ray Scattering (SAXS) Study

Structure of diglycerol monomyristate (designated as C14G2) nonionic surfactant reverse micelles in aromatic solvent styrene has been investigated as a function of surfactant concentration, temperature, and water addition by using small-angle X-ray scattering (SAXS) technique. Structure of micelles in real-space so called pair-distance distribution function, p(r), was obtained by the generalized indirect fourier transformation (GIFT) evaluation of SAXS data. It was found that C14G2 spontaneously self-assembles into spheroid reverse micelles with maximum diameter approximately 3.0 nm when added into styrene under ambient condition. The micellar shape and size remained essentially the same despite a wide variation in surfactant concentration (5 to 30%) but an opposite trend was observed with the rise of temperature; size decreased by approximately 25% with increase in temperature from 25 to 75 degrees C. Addition of traces water favored micellar growth and eventually ellipsoid prolate type micelles were formed, whose scenario is understood in terms of decrease in the critical packing parameter (cpp); water hydrates the surfactant's headgroup and decreases cpp. At a particular concentration of water, increasing temperature decreased the micellar size due to dehydration of headgroup. It is interesting to note that size of 1.57% water incorporated micelle is approximately 2.5 times bigger than the empty micelles.

Intrinsic Parameters for the Structure Control of Nonionic Reverse Micelles in Styrene: SAXS and Rheometry Studies

Shape, size, and internal structure of nonionic reverse micelle in styrene depending on surfactant chain length, concentration, temperature, and water addition have been investigated using a small-angle X-ray scattering (SAXS) technique. The generalized indirect Fourier transformation (GIFT) method has been employed to deduce real-space structural information. The consistency of the GIFT method has been tested by the geometrical model fittings, and the micellar aggregation number (N(agg)) has been determined. It was found that diglycerol monocaprate (C(10)G(2)), diglycerol monolaurate (C(12)G(2)), and diglycerol monomyristate (C(14)G(2)), spontaneously self-assemble into reverse micelles in organic solvent styrene under ambient conditions. The micellar size and the N(agg) decrease with an increase in surfactant chain length, a scenario that could be understood from the modification of the critical packing parameter (cpp). A clear picture of one-dimensional (1-D) micellar growth was observed with an increase in surfactant weight fraction (W(s)) in the C(10)G(2) system, which eventually formed rodlike micelles at W(s) ≥ 15%. On the other hand, micelles shrunk favoring a rod-to-sphere type transition upon heating. Reverse micelles swelled with water, forming a water pool at the micellar core; the size of water-incorporated reverse micelles was much bigger than that of the empty micelles. Model fittings showed that water addition not only increase the micellar size but also increase the N(agg). Zero-shear viscosity was found to decrease with surfactant chain but increase with W(s), supporting the results derived from SAXS.

SAXS Study on Azithromycin Loaded Nonionic Microemulsions

Abstract Structure of water/propylene glycol/ethoxylated mono-di-glyceride/peppermint oil/ethanol microemulsions solubilizing azithromycin has been investigated at room temperature by small-angle X-ray scattering (SAXS) technique. The scattering data were evaluated by Indirect Fourier Transformation (IFT) or Generalized Indirect Fourier Transformation (GIFT) methods depending on the aqueous phase content. The growth of the microemulsions droplets by increasing the water content and the effect of azithromycin incorporation in the microemulsions were investigated. The Indirect Fourier Transformation gives the real space pair-distance distribution function: a facile way for the quantitative estimation of structure parameters of the microemulsions. It was found that the size of the microemulsion aggregates or repeating distances in the microemulsion increases with the aqueous phase content. The maximum diameter of the drug free and drug loaded microemulsions aggregates depend on their microstructure. The values of the effective interaction radius of the microemulsions are higher for the drug free compared to the drug loaded microemulsions aggregates.

Water-in-oil-in-water double nanoemulsion induced by CO2

The cetyltrimethylammonium bromide (CTAB)/water/heptane emulsion system with different CO(2) pressure has been studied. The phase behavior investigation shows the nanoemulsion can be formed at suitable pressure range. The generalized indirect Fourier transformation (GIFT) analysis of the small-angle X-ray scattering (SAXS) data has drawn a clear picture of the structural information of the nanoemulsion, which reveals that the droplet of emulsion has a double structure with both the outer and inner droplet size in nanometre range. Furthermore, the investigation of the heptane/CTAB/water/CO(2) emulsion system by using electrical conductivity confirms the emulsion type transforms from O/W to W/O/W. In addition, the effect of different CTAB concentration on the nanoemulsion formation has been studied. It is found that enough CTAB concentration is necessary for the inclusion of continuous water into oil droplets. We also explored the application of the W/O/W double nanoemulsion in material synthesis. Interestingly, the hollow silica spheres with double shells were obtained in this CO(2)-induced double nanoemulsion.

Reverse micelle microstructural transformations induced by oil and water

Effects of alkyl chain length of oil and water on the shape, size, and internal structure of glycerol monooleate (GMO) reverse micelle have been investigated using small-angle X-ray scattering (SAXS) and rheometry techniques. The generalized indirect Fourier transformation (GIFT) method has been employed to analyze the SAXS data, also supported by the direct modeling. It has been found that under ambient conditions the GMO spontaneously self-structure into an ellipsoidal prolate type micelle with a maximum size of ca. 5.7 nm in n-hexane and the size increases in parallel to the chain length of oil reaching a size of ca. 10.7 nm in n-hexadecane. However, the micellar core radius remains essentially the same, i.e., the growth is one dimensional. The increasing tendency of zero-shear viscosity, η0, with the chain length of oil further confirmed the micellar growth. The relative viscosity, ηr, of the reverse micelles was higher and exhibited a steeper solvent (chain length) dependence behavior than those predicted for a dispersion of spherical particles based on the Krieger–Dougherty relation sustaining the SAXS results. The micelles swell with water causing a significant micellar growth; the maximum size and core radius of 0.3% water incorporated reverse micelles were found to be respectively 53%, and 28% larger than the empty micelles.

SAXS and Rheometry Studies of Diglycerol Monolurate Reverse Micelles in Styrene

We have investigated the structure and rheology of diglycerol monolaurate (C(12)G(2)) reverse micelles in styrene using small-angle X-ray scattering (SAXS) and rheometry techniques. The SAXS data have been evaluated by generalized indirect Fourier transformation (GIFT) method and further supported by geometrical model fittings. We found that the C(12)G(2) when added into styrene spontaneously self-assemble into ellipsoidal prolate type reverse micelles under ambient conditions. Micelles grew and micellar aggregation number (N(agg)) increased with the increase in surfactant concentration demonstrating concentration induced one dimensional micellar growth, which was further supported by rheology data; the relative viscosity, η(r), for the C(12)G(2)/styrene mixtures exhibit far steeper concentration dependence behavior than those predicted for a dispersion of spherical particles based on the Krieger-Dougherty relation, due to the elongated micellar structures. On the other hand, a distinct modulation in the shape and size of micelles favoring ellipsoidal prolate-to-sphere type transition was observed upon heating, whose scheme could be attributed to the enhanced penetration tendency of oil into the lipophilic shell of the surfactant at the higher temperatures. As anticipated reverse micelles swelled with water causing two dimensional micellar growth; both the maximum dimension and maximum core radius increase with water.

Microstructure of supercritical CO2-in-water microemulsions: a systematic contrast variation study

Microemulsions of the type H(2)O-scCO(2)-surfactant are potential candidates for novel solvent mixtures in the field of green chemistry. Furthermore, scCO(2)-microemulsions are highly interesting from a fundamental point of view since their properties such as the bending elastic constants can be strongly influenced solely by varying the pressure without changing the components. With this motivation we studied the phase behavior and the microstructure of water-rich scCO(2)-microemulsions. Such microemulsions were formulated using the technical grade non-ionic surfactants Zonyl FSO 100 and Zonyl FSN 100. At elevated pressures the temperature dependent phase behavior of these systems follows the general patterns of non-ionic microemulsions. Small angle neutron scattering experiments were conducted to determine the length scales and the topology of the microstructure of these systems. Having determined the exact scattering length densities and the composition of the respective sub-phases by a systematic contrast variation we could show that these systems consist of CO(2)-swollen microemulsion droplets that are dispersed in a continuous aqueous-phase. The scattering data were analyzed using a newly derived form factor for polydisperse, spherical core/shell particles with diffuse interfaces. The underlying analytical density profiles could be confirmed applying the model-free Generalized Indirect Fourier Transformation (GIFT) to the scattering data. Following the general patterns of non-ionic microemulsions the radius of the microemulsion droplets is found to increase almost linearly upon the addition of CO(2).

Structural Characterization of Nonionic Surfactant Reverse Micelles in Diglycerol Monolaurate/Squalene System

Structure of nonionic surfactant diglycerol monolaurate (C12G2) reverse micelles in squalene at different surfactant concentrations and temperatures is presented. For the structural characterization of the micelles, small-angle X-ray scattering (SAXS) technique is used. The scattering data is evaluated by virtually model free generalized indirect Fourier transformation (GIFT) method. GIFT analysis of the SAXS data has shown the clear evidence on the formation of rod-like micelles in the C12G2/squalene system at higher temperatures. At fixed temperature, increasing surfactant concentration induces one-dimensional micellar growth; the maximum length of the micelles increases with concentration, but the micellar cross-section remains essentially the same. On the other hand, at fixed concentration, the maximum length of the micelles decreases with the rise of temperature. It is found that the length of micelles decreases by ~ 35% keeping cross-section diameter unchanged with the rise of temperature from 60 to 80 °C in 5 wt% wt% C12G2/squalene system.