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Nanoconfined water exhibits various interesting properties, which are not only of fundamental importance but also of practical use. Because reverse micelles (RMs) provide versatile ways to prepare nanoconfined water, the understanding of their physicochemical properties is essential for developing efficient applications. Although the water properties in the RMs could be affected by its interaction with the RM interface, the details have not been well understood. This study focuses on the local structures of Br− in hexadecyltrimethylammonium bromide (HTAB) RMs formed in chloroform and 10% hexanol/heptane. The dependence in Br− hydration on the molar ratio of water to HTAB (w) is investigated using X-ray absorption fine structure (XAFS). These systems cover a wide range of w values (0–30) and allow us to study the impact of this parameter on the local structure of Br− at the RM interface, which comprises water, surfactant headgroups, and organic solvent components. The presence of multiple scattering paths complicates the XAFS spectra and makes it difficult to analyze them using standard fitting methods. The linear combination of the spectra corresponding to the individual scattering paths captures the molecular processes that occur at the RM interface upon increasing w. The maximum hydration number of Br− is found to be 4.5 at w > 15, suggesting that although most of the ions remain at the interface as partly hydrated ions, some of them dissociate as completely hydrated ones.

Hypothesis: By combining the experimental small- and wide-angle x-ray scattering (SWAXS) method with molecular dynamics simulations and the theoretical 'complemented-system approach' it is possible to obtain detailed information about the intra- and inter-molecular structure and dynamics of the solvation and hydration of the surfactant in organic and mixed solvents, e.g., of the nonionic surfactant Brij 35 (C12E23) in alcohols and aqueous alcohol-rich ternary systems. This first application of the complemented-system approach to the surfactant system will promote the use of this powerful methodology that is based on experimental and calculated SWAXS data in studies of colloidal systems. By applying high-performance computing systems, such an approach is readily available for studies in the colloidal domain. Experiments: SWAXS experiments and MD simulations were performed for binary Brij 35/alcohol and ternary Brij 35/water/alcohol systems with ethanol, n-butanol and n-hexanol as the organic solvent component at 25 {\deg}C. Findings: We confirmed the presence of solvated Brij 35 monomers in the studied organic media, revealed their preferential hydration and discussed their structural and dynamic features at the intra- and inter-molecular levels. Anisotropic effective surfactant molecular conformations were found. The influence of the hydrophobicity of the organic solvent on the hydration phenomena of surfactant molecules was explained., Comment: 31 pages, 6 figures, 1 table

Hypothesis The dynamic nature of the oil-water interface allows for sequestration of material within the dispersed domains of a microemulsion. Microstructural changes should therefore change the dissolution rate of a solid surface in a microemulsion. We hypothesize that microstructural changes due to formulation and cavitation in an acoustic field will enable control over solid dissolution rates. Experiments Water-in-oil microemulsions were formulated using cyclohexane, water, Triton X-100, and hexanol. The microstructure and solvation properties of Winsor Type IV formulations were characterized. Dissolution rates of KH2PO4 (KDP), were measured. A kinetic analysis isolated the effect of the microstructure, and rate enhancements due to cavitation effects on the microstructure were characterized by measuring dissolution rates in an ultrasonic field. Findings Dispersed aqueous domains of 2–6 nm radius dissolve a solid block of KDP at 0–10 nm/min. Dissolution rate is governed not by the domain-surface collision frequency but rather by a dissolution probability per domain-surface encounter. Higher probabilities are correlated with larger domains. Rapid and reversible dissolution rate increases of up to 270× were observed under ultrasonic conditions, with

The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.

The interfacial composition and the structure of the water/C12– EO x –C12⋅2Br/n-hexanol/n-heptane microemulsion have been investigated by the dilution method. The results showed that C12– EO x –C12⋅2Br formed a stable water/oil microemulsion with the assistance of n-hexanol. Owing to the relatively large size of the head group, more n-hexanol molecules are populated on the droplet surface than in the C12–2–C12⋅2Br system. The radius of the water pool of the C12–EO3–C12⋅2Br system is not as sensitive to W 0 as in the C12–2–C12⋅2Br system. Another feature of the present system is that its droplet size is considerably smaller than that of the C12–2–C12⋅2Br system, and also those of the CPC and CTAB systems at relative high water content. This provides a potential application for the synthesis of nanoparticles with small size.

We have studied the effect of adding a water-soluble polymers (PEG) to the lamellar phases of the ternary system tetradecyldimethylaminoxide (C14DMAO)-hexanol-water. The results of Freeze-Fracture Electron Microscopy (FFEM) and Small Angle X-ray Scattering (SAXS) experiments show that the addition of the polymer induces the spontaneous formation of highly monodisperse multilayered vesicles above a threshold polymer concentration.

The Wells-Dawson tungsten heteropolyacid, H6P2W18O62 supported on sol-gel and non-sol-gel alumina has been investigated by infrared spectroscopy (IR), thermal analysis (TGA/DSC), and X-ray diffraction (XRD). X-ray diffraction indicates that the heteropolyacid primary structure in bulk form holds up to 350 degrees C and by supporting it on the sol-gel alumina the thermal stability rose to 650 degrees C. UV-vis spectroscopy showed that the sol-gel alumina has a higher tendency to adsorb Wells-Dawson tungsten heteropolyacid than the non-sol-gel alumina. The heteropolyacid showed higher interaction with the sol-gel alumina than with the non-sol-gel. Esterification of propanoic acid with hexanol in the presence of alumina-supported heteropolyacid revealed that the acidic character of the heteropolyacid remains active to some extent.

The dissociation of tris-(2,2'-bipyridyl) iron(II) ([Fe(bipy)(3)](2+)) has been studied in the Triton X-100/hexanol/cyclohexane reverse micellar medium. The reaction obeys simple first-order kinetics with no evidence of autoinhibition. The first-order rate constant (k(1)) has been determined at different values of W ([H2O]/[Triton X-100]). The rate (k(1)) decreases with increasing value of W. k(1) also increases with increase in Triton X-100 concentration at constant values of W, showing that the reaction takes place at greater speed at the micellar interface. The kinetic results can be interpreted by the monomolecular pseudo-phase model. The effect of W on rate (k(1)) is more pronounced in the range of W from 1.55 to 4.2 but less pronounced at higher W. The reaction is further accelerated by Cl- and SCN- ions and the kinetic results provide evidence for the formation of ion pairs between the cation [Fe(bipy)(3)](2+) and each of these anions. The formation of such ion pairs has not been observed in aqueous medium but has been reported earlier in aqueous-alcohol mixtures. This result therefore provides evidence for the lower micropolarity of solubilized water compared to ordinary water. (c) 2005

This paper focuses on the characterization and use of polymer-modified phosphatidylcholine (PC)/sodium dodecyl sulfate (SDS)-based inverse microemulsions as a template phase for BaSO4 nanoparticle formation. The area of the optically clear inverse microemulsion phase in the isooctane/hexanol/water/PC/SDS system is not significantly changed by adding polyelectrolytes, i.e., poly(diallyldimethylammonium chloride) (PDADMAC), or amphoteric copolymers of diallyldimethylammonium chloride and maleamid acid to the SDS-modified inverse microemulsion. Shear experiments show non-Newtonian flow behavior and oscillation experiments show a frequency-dependent viscosity increase (dilatant behavior) of the microemulsions. Small amounts of bulk water were identified by means of differential scanning calorimetry. One can conclude that the macromolecules are incorporated into the individual droplets, and polymer-filled microemulsions are formed. The polymer-filled microemulsions were used as a template phase for the synthesis of BaSO4 nanoparticles. After solvent evaporation the nanoparticles were redispersed in water and isooctane, respectively. The polymers incorporated into the microemulsion are involved in the redispersion process and influence the size and shape of the redispersed BaSO4 particles in a specific way. The crystallization process mainly depends on the type of solvent and the polymer component added. In the presence of the cationic polyelectrolyte PDADMAC the crystallization to larger cubic crystals is inhibited, and layers consisting of polymer-stabilized spherical nanoparticles of BaSO4 (6 nm in size) will be observed.

Positron annihilation lifetime parameters in condensed media are sensitive to structural and conformational changes. This property has been exploited to study the phase diagrams of two ternary cationic surfactant systems. Positron lifetime measurements were performed in cetyltrimethylammonium bromide (CTAB)/water/hexanol and tetradecyltrimethylammonium bromide (TTAB)/water/pentanol systems having varying concentrations of hexanol and pentanol respectively. For both the systems, changes were observed in the positron lifetime parameters whenever a phase transformation occurred. The various phase boundaries demarcated by this technique agrees well with those obtained by other conventional techniques. Besides this, the present work suggests the existence of two kinds of lamellar structures referred to as DI and DII phases in both the systems, which were otherwise considered to be a single D phase by other conventional techniques. The existence of such lamellar structures has been demonstrated by a change in the trend of o-Ps lifetime when the system passes from one type of lamellar structure to the other type. The results of these investigations are presented.

A systematic study on phase behavior of the mixture of nonionic surfactants with alcohols at 30.0+/-0.1 degrees C was carried out. The total surfactant concentration was kept to 0.1 M varying the mole ratio of n-octyl beta-d-glucopyranoside (OG) and tetraethylene glycol monododecyl ether. Two uniphasic regions were found, the lamellar phase at low OG mole fraction and micelles at high OG mole fraction. The presence of OG favors the lamellae-micelle transition. Alkanols and benzyl alcohol were used as cosurfactants. The more hydrophobic alcohols (octanol and decanol) increase the OG content in the mixed bilayers. On the contrary, benzyl alcohol is not as favorable to the OG incorporation in the lamellar phase as in the mixed micelles. The L(3) phase has only been found as a uniphasic region with hexanol.

Various catalysts consisting of sodium-magnesium mixed orthophosphates were synthesized and characterized in structural terms using X-ray diffraction, thermogravimetric analysis, differential thermal analysis, diffuse reflectance infrared spectroscopy, and solid-state (31)P NMR spectroscopy. In addition, the surface properties of the solids were determined from N(2) adsorption-desorption isotherms and their chemical properties characterized with various titrants. One of the solids obtained consists of NaMgPO(4)/Mg(2)P(2)O(7) and the rest of NaMgPO(4)/MgO. Their surface chemical properties vary depending on the particular synthetic procedure used; thus, the NaMgPO(4)/MgO systems exhibit similar populations of acid and basic sites, whereas the NaMgPO(4)/Mg(2)P(2)O(7) systems contain many more acid sites than basic sites. All the solids obtained exhibit substantial dehydrogenating activity in the conversion of gaseous 2-hexanol; in fact, some of the NaMgPO(4)/MgO systems are even more active and selective than a MgO solid tested under identical reaction conditions. Copyright 2001 Academic Press.

The spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)-pyrido[3,4-d]imidazole (DMAPPI) have been studied in a TritonX-100 (TX-100)/n-hexanol/water reverse micelle in cyclohexane as a function of water (w(0)), surfactant, cosurfactant, pH, and trifluoroacetic acid. Under the neutral conditions, dual fluorescence (normal and twiste intramolecular charge transfer) is observed, even at w(0)=0, suggesting that the TICT state is stabilized by the hydrogen bonding from n-hexanol. These studies indicate that DMAPPI molecules are present near the interface of the water pool and the micellar phase toward the micellar side, and the changes observed in the spectral characteristics with change of w(0) are due to the formation of the reverse micelles and the alignment of cosurfactant around DMAPPI. Variation of pH in the range 3-10 has no effect on the spectral characteristics of DMAPPI, suggesting that the protons do not penetrate the reverse micelles, whereas the trifluoroacetic acid protonates DMAPPI to form monocations (MCs). At w(0)=0, MC2 and MC3 (see Scheme 1) are the MCs present both in the S(0) and S(1) states, whereas with an increase in w(0), the MC2 shifts toward MC1. Biprotonic phototautomerism is observed in MC1, which leads to the formation of MC2 in the S(1) state. Copyright 2000 Academic Press.

The photophysics of a fluorescent drug Piroxicam was used to probe the intramicellar region of nonionic microemulsions of Triton X-100/cyclohexane—hexanol/water, using both steady-state and transient (picosecond resolution) techniques. A protic and polar interface, as inferred from the calculated Kamlet-Taft parameters (α and π*), interacts with the probe as a Lewis base. Three distinct spectroscopic species were detected with pH-dependent contributions. Such dependence is noted only above a certain water concentration (ω0=8), confirming the existence of water pools thereafter. Transient data lead to similar conclusions. A global analysis of the fluorescence decays was made and three different lifetimes were obtained. The shortest (τ1=16 ps) and the longest (τ3=2.02 ns) correspond to those already found in free aqueous solution. An intermediate component (τ2=72 ps), whose importance grows with the amount of solubilized water at pHext 4, is thought to represent a less protic and more rigid environment, which is sensed by the probe. An increase in the microviscosity values also detected by fluorescence anisotropy and the lower α and π*, calculated 0.5 and 0.7, respectively, contribute to this statement. Major changes observed in the system around ω0=8 are emphasized, taking into account a dynamic light-scattering study, where a dependence of the hydrodynamic radius on the observation angle is detected above this water content.

The phase diagram of the ternary surfactant system tetradecyldimethylamine oxide (TDMAO)/HCl/1-hexanol/water shows with increasing cosurfactant concentration an L(1) phase, two L(alpha) phases (a vesicle phase L(alpha1) and a stacked bilayer phase L(alphah)), and an L(3) phase, which are separated by the corresponding two-phase regions L(1)/L(alpha) and L(alpha)/L(3). In this investigation, the system was studied where some of the TDMAO was substituted by the protonated TDMAO. Under these conditions, one finds for constant surfactant concentration of 100 mM TDMAO a micellar L(1) phase, an L(alpha1) phase (consisting of multilamellar vesicles), and an interesting isotropic L(1)(*) phase in the middle of the L(1)/L(alpha) two-phase region. The L(1)(*) phase exists at intermediate degrees of charging of 30-60% and for 40-120 mM TDMAO and 70-140 mM hexanol concentration. At surfactant concentrations less than 80 mM the L(1)(*)-phase borders directly on the L(1) phase. The phase transition between the L(1) phase and the L(1)(*) phase was detected by electric conductivity and rheological measurements. The conductivity values show a sharp drop at the L(1)/L(1)(*) transition, and the zero shear viscosity of the L(1)(*) phase is much lower than in L(1) phase. The form and size of the aggregates in L(1)(*) were detected with FF-TEM and SANS. This phase contains small unilamellar vesicles (SUV) of about 10 nm and some large multilamellar vesicles with diameters up to 500 nm. The system exhibits another peculiarity. For 100 mM surfactant, the clear L(alpha1)-phase exists only at chargings below 30%. With oscillating rheological measurements a parallel development of the storage modulus G' and the loss modulus G" was observed. Both moduli are frequency independent and the system possesses a yield stress. The storage modulus is a magnitude larger than the loss modulus. Copyright 2000 Academic Press.

Hollow-shell micrometer-sized particles were fabricated in aqueous media by stepwise deposition of oppositely charged polyelectrolytes onto melamine latex particles and biological cells with a dissolution of the core afterward. It is demonstrated that these shells can be suspended in various organic media, such as methanol, ethanol, pentanol, hexanol, octanol, octane, and decane, by a gradual solvent exchange. At this stage of the procedure the shells contain the respective organic solvent. Oil suspensions in water are then formed by transferring the particles from the organic media into water, without the use of any further surfactant addition. By an additional adsorption step employing phospholipids, it is possible to obtain a dispersion of shells in organic solvents containing an aqueous solution inside. AFM measurements are provided which show that the shells preserve their integrity in the different solvents. Confocal microscopy is employed to demonstrate encapsulation of solvents and the presence of lipids. Copyright 1999 Academic Press.

Based on the studies of their physical properties such as aqueous solution uptake, electric conductivity, and microstructure, CTAB/hexanol/water reverse micelles (CTAB, cetyltrimethyl ammonium bromide) were used to prepare ZrO2-Y2O3 nanoparticles. The relationship between the micelle microstructure and size, morphology, and aggregate properties of particles prepared was also investigated. It has been found that with high CTAB concentration ([CTAB] > 0.8 mol/l), the reverse micelles can solubilize a sufficient amount of aqueous solution with high metallic ion concentration ( approximately 1.0 mol/L), while the microstructure of the reverse micelles keeps unchanged. The most important factor affecting the size and shape of reverse micelles was found to be the water content w0 (w0, molar ratio of water to surfactant used). When both the CTAB concentration and the w0 values are low, the diameters of reverse micelles are below 20 nm, and the ZrO2-Y2O3 particles prepared are also very small. However, the powders obtained were found to form a lot of aggregates after drying and calcination. High CTAB concentration, high w0 value, and high metallic ion concentration in the aqueous phase for high powder productivity were found to be the suitable compositions of reverse micelles for preparing high-quality ZrO2-Y2O3 nanoparticles. Under these conditions, the reverse micelles are still spherical in shape even the reverse micellar system is nearly saturated with aqueous solutions. These reverse micelles were found to have a diameter of between 60 and 150 nm and the ZrO2-Y2O3 particles prepared therefrom range from 30 to 70 nm with spherical shape and not easy to form aggregates. Copyright 1999 Academic Press.

The phase behavior and solubilization of multiphase microemulsions in mixed anionic-cationic surfactant systems were studied for fixed ratios of water-to-oil and surfactant-to-alcohol. In the mixed surfactants (sodium dodecyl sulfate + cetyltrimethylammonium bromide)/heptane/alcohol/water systems, microemulsion and birefringent phases are formed by adjusting the surfactant ratio epsilon and the cationic weight fraction delta. The bicontinuous (or w/o microemulsion) --birefringent o/w microemulsion transition takes place and microemulsion domain enlarges with increasing epsilon. The optimum surfactant concentration gamma increases and the corresponding optimum delta decreases with increasing epsilon and both of them decrease with increasing the alcohol chain length from butanol to hexanol. The birefringent region shrinks rapidly with increasing alcohol and/or CTAB weight fractions in total surfactant concentration. Conductivity measurements have been performed in the single-phase region of the system containing mixed surfactants and alcohols at 25deg;C. The conductivity results indicate where a transition takes place and which of these different types of phase structures may be in the single-phase of the system containing anionic-cationic mixed surfactants.

The surface tension of the aqueous solution of a 1-hexanol and 2-(octylsulfinyl)ethanol (OSE) mixture was measured as a function of the total concentration of 1-hexanol and OSE and the mole fraction of OSE in the total surfactant. The total surface density of 1-hexanol and OSE and the compositions in the adsorbed film and micelle were obtained by applying the thermodynamic equations. The phase diagrams analogous to those of binary mixtures were drawn for the adsorption and micelle formation. 1-Hexanol and OSE molecules were found to be miscible with each other in all proportions in the adsorbed film and partially in the micelle. Both the adsorbed film and micelle were richer in OSE than the solution. A great discrepancy in composition was observed between the adsorbed film and micelle coexisting in equilibrium at the critical micelle concentration. The discrepancy was ascribed to the large difference in size and property of head group. Further, a negative deviation from the ideal mixing was found in the adsorbed film. The large negative value of the excess Gibbs free energy was observed over the whole range of composition of the adsorbed film, which was attributed to a large attractive interaction between 1-hexanol and OSE molecules in the adsorbed film.

Middle-phase microemulsion (surfactant phase) is formed in a water/sucrose monododecanoate (SE)/hexanol/decane system. Based on the geometrical relations of a particular three-phase triangle in the quaternary system, the monomeric solubility of hexanol in the excess oil phase and the mixing fraction of SE and hexanol at the water–oil interface inside the microemulsion were obtained. Both values are almost unchanged with increasing temperature. This phase behavior is completely different from that for a system including an ordinary polyoxyethylene-type nonionic surfactant and resembles that in a brine/ionic surfactant/cosurfactant/oil system. On the other hand, the solubilization capability of the SE–hexanol mixtures decreases at higher temperatures due to the decrease in the compatibility of the microemulsion with oil. However, the mixing ratio of mixed surfactant for the maximum solubilization is not greatly changed. Consequently, temperature-insensitive microemulsions can be attained in the present SE system. The effect of oil or surfactant chain length on the phase behavior is also discussed.

The adsorption of 1-butanol and 1-hexanol vapors on various solid samples was investigated in relation to the gradient of the linear portion of Type II isotherms. The adsorption isotherms of the medium-sized normal alcohol vapors were classified as either typical Type II or those resembling Type I isotherms. The former were shown by samples of gold, aluminum, and graphite, and the latter by samples of alumina, sodium chloride, and silicate glass. BET surface areas and gradient method surface areas by these alcohol adsorbates were estimated for each solid sample, and from the latter, excess entropy of adsorbed molecules of the alcohol adsorbates was estimated by the gradient method theory for surface area measurement. Excess entropy showed that the molecules adsorbed on gold in the multilayer region had almost the same kinetic freedom as the molecules in the liquid state and showed the applicability of the gradient method to this kind of solid. Excess entropy of adsorption also showed that the molecules on alumina, sodium chloride, and porous silica glass had less kinetic freedom than the liquid-state molecules by the entropy reduction of 25 to 30% compared to the solidification entropy change.

Light scattering and small-angle neutron scattering have been examined for the L 1 phase of dodecyldimethylamine oxide (C 12 DAO)/hexanol/water system as a function of the mole fraction of hexanol, x . The molecular weight evaluated from light scattering increased from 1.54 × 10 4 at x = 0 to 20.4 × 10 4 at x = 0.44, while the hydrodynamic radii were 56 and 98 A at x = 0.33 and 0.44, respectively. Guinier plots on small-angle neutron scattering decreased with downward curvature for solutions in the L 1 phase. An electron micrograph displayed the images of globular particles of 50-400 A diameter, indicating the polydispersity in particle size. The numerical analysis based on the theoretical aspect for polydisperse spherical particles confirmed that molecular assemblies in the L 1 phase exhibited the bimodal distribution: spherical micelles of 44 A diameter coexisted with microemulsions of 260 A diameter, which were hexanol droplets stabilized by shells of surfactant molecules.

The effect of medium chain length alcohols on the micellar size and shape of sodium dodecyl sulfate in electrolyte solutions has been investigated by means of small angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. The surfactant content was kept constant throughout, at 0.04 m, and the alcohols used were 1-butanol, 1-pentanol, and 1-hexanol. The data from the various techniques are qualitatively in agreement. The SANS data generally fit a model for prolate ellipsoids with varying ratios of the major to minor axis. Addition of butanol first leads to a decrease in micellar size, the major to minor axis ratio decreases from about 6 to less than 2. However, as the butanol concentration exceeds 0.5 m, the micelles starts to grow again. The same can be seen from the diffusion coefficient as measured by DLS. Addition of pentanol or hexanol do not bring about this minimum in micellar size. The minor axis decreases and the major axis increases as these alcohols are added. Thus these alcohols make the prolate ellipsoidal micelles grow continuously towards large rod-like structures. The viscosity data are less detailed, but confirm the general trend upon alcohol addition.

The influence of ionic charges on the mesophases in the ternary phase diagram of tetradecyldimethylaminoxide (C14DMAO), hexanol, and water was studied. The charges were introduced by replacing C14DMAO by the cationic surfactant tetradecyltrimethylammonium bromide (C14TMAB). The phase diagram becomes much simpler by this substitution. The L1- , L3-, and L3-phases which had previously been observed for the uncharged system are very sensitive to the charges and disappear completely with increased mole fraction of C14TMAB (Xc > 0.2). Furthermore, the Lα1 - and the Lαh-phases merge into a single Lα-phase which has properties similar to those of the Lα1-phase in the uncharged system. The most prominent feature of the charged Lα-phase is its theological yield stress value. With increasing Xc the phase boundaries of the L1- and the Lα-phase are shifted to a higher mole fraction of alcohol (Xa). The two phase regions (L1 + Lα) widen with increasing X c. Samples in this two phase region separate easily into two phases. The properties of the different phases were determined and characterized by conductivity and theological measurement and by polarization microscopy. FF-TEM micrographs show that the charged Lα-phase consists over the whole existence region of single and multilamellar vesicles. The vesicles at the lower phase boundary (low Xa-values) seem to have defects which disappear with increasing Xa-values. Finally, it is shown that with the addition of excess salt the phase diagram with the charged surfactant behaves again in the same way as the uncharged system.

Phase behavior in a NaCl/water/sodium octyl sulfonate (R8SO3Na)/hexanol/isooctane system was systematically investigated at constant pressure. Three-phase body containing water, surfactant (middle-phase microemulsion, D), and oil phases appears at a tricritical point at higher temperatures, whereas it appears via a four-phase region at lower temperatures. The four-phase body is formed by overlapping the three-phase body and another three-phase body including another surfactant phase (D′). We have investigated how the tricritical point or the four-phase body is produced from systems of fewer components. The effects of temperature and other variables on the tricritical point and the four-phase body are discussed. A possible explanation for the origin of the three-phase body (the existence of a tricritical endpoint) is given.

Aqueous surfactant solutions of tetradecyldimethylaminoxide (TDMAO) and tetradecyltrimethylammoniumbromide (TTMAB) in the presence of increasing amounts of hexanol were studied in the L1-phase region. TDMAO forms rod-like and TTMAB globular micelles in the concentration range between 50 and 100 mM. In all mixtures with a mol fraction Xc > 0.1 of cationic surfactant globular micelles are found. Hexanol was added to the surfactant mixtures until the phase boundary of the L1 phase was reached. The micellar structures and the properties of the surfactant solutions were studied with surface and interfacial tension, electric birefringence, viscosity, and conductivity measurements. A sphere-rod transition was observed in all surfactant mixtures with increasing hexanol concentration. In the pure cationic system globular micelles were observed with increasing mol fraction of alcohol Xa, up to the phase boundary. Electric birefringence measurements turned out to be most sensitive to the sphere-rod transition. The hexanol concentration which was necessary to reach the sphere-rod transition increased continuously with Xc . The concentration of hexanol to reach the phase boundary increased also. The viscosities, the rotational time constants, and the Kerr constants of the mixed surfactant solutions increased exponentially with the hexanol concentration from the sphere-rod transition to the phase boundary. The viscosity which was reached close to the phase boundary decreased with increasing mol fraction of the cationic surfactant. The lengths of the rods at the phase boundary which were determined from the electric birefringence measurements decreased with increasing Xc. The persistence length for all charged and unshielded rods seems to be longer than their total length and the rods under these conditions can be visualized as being stiff. The surface and the interfacial tension for all micellar solutions decreased in a similar fashion with increasing Xa. Independently of Xc the interfacial tension of the micellar solution measured against decane, reached a value of about 0.2 mN/m at the phase boundary. The surface tension was around 25 mN/m and also more or less independent on the surfactant ratio.

It was found that stable reverse vesicles of sucrose monoal-kanoate form in decane + hexanol in the presence of a small amount of water. They are the dispersion of lamellar liquid crystal which swell a considerable amount of oil. The interlayer spacing of the bilayers is increased upon addition of hexanol. As a result, hexanol is effective in making the bilayers flexible and in dispersing the liquid crystal as reverse vesicles. The structure of the reverse vesicles was confirmed by video-enhanced microscopy, fluorescence microscopy, and freeze-fracture transmission electron microscopy(Cryo-TEM). The orientation of amphiphilic molecules is completely opposite to that in normal vesicles, i.e., with the hydrophilic part located inward. The thickness of the bilayers (about 10 nm) observed from Cryo-TEM photography is in good agreement with SAXS (small-angle X-ray scattering) data. The smaller vesicles with sizes of submicrometer order are very stable and are not precipitated for several months.

The enthalpies of transfer from water to the surfactant solutions ΔH(W → W + S) of some hydrogenated and fiuorinated alkanols and of sodium dodecanoate NaL were determined. In the premicellar region the measurements were carried out as functions of both the additive and the surfactant concentrations in order to evaluate the interaction parameters between the additive and the surfactant molecules. It is shown that in this region, pair, triplet, and quadruplet interaction parameters between unlike solute molecules contribute to ΔH(W → W + S). Within the large uncertainty with which these parameters are determined because of the very narrow surfactant and alcohol concentration interval investigated, these parameters change regularly with the number of carbon atoms in the alkanols alkyl chain. In the post-micellar region the measurements were made at a given additive concentration by systematically changing the surfactant concentration. As expected, ΔH(W → W + S) increases with the surfactant concentration for all alcohols with the exception of pentanol and hexanol for which at higher surfactant concentrations ΔH(W → W + S) decreases. In addition, for the investigated systems a minimum, which becomes more important the longer the alkyl chain length, is present at NaL 0.08 m. Experimental data (with the exception of perfluoroethanol and propanol for which all experimental points have been considered) ranging between this concentration and the CMC were rationalized using a previously reported model for the additive distribution between the aqueous and the micellar phases. From this model the distribution constant and the standard transfer enthalpy (and, then, the standard free energy and entropy) are simultaneously obtained. The absolute values of all properties are smaller for the hydrogenated alcohols with respect to the fluorinated ones.

Aqueous solutions of octadecyldimethylamine oxide (C 18 DAO), diglycerol isostearyl ether (C 18 DGE), and tetradecyldimethylamine oxide (C 14 DAO)/hexanol/decane were observed by transmission electron microscopy. While plate-like assemblies, unilamellar vesicles, or globular microemulsions are formed in dilute solutions of C 18 DAO, C 18 DGE, or C 14 DAO/hexanol/decane, multilamellar layers, multilamellar vesicles, or multilamellar microemulsions, respectively, exist in their iridescent solutions. On the other hand, lamellar liquid crystal is formed in concentrated solutions of C 18 DAO and C 18 DGE.

Calorimetric measurements have been used to study the shape transitions of micelles. Partial molar enthalpies of solutions of cosurfactants (n-pentanol, benzyl alcohol, 3-methyl-l-butanol, n-hexylamine) have been measured in 2% TTMAB solutions at 25 and 45°C with various electrolytes (NaCl, NaBr, NaSCN, NaF, NaNO3, KCI, KBr, NaOH, LiCl, BaCl2, NaI) and nonelectrolytes (dioxane, urea, nhexylamine, benzyl alcohol, hexanol ). Some measurements were made on 3.5% SDDS solution at 45°C. The break in the plot of partial molar enthalpy of solution of cosurfactants vs cosurfactant concentration was observed in both TTMAB and SDDS solutions. The end of this break observed calorimetrically corresponds to the sphere-rod transition observed with light-scattering. Counterion ability to induce the TTMAB sphere-rod transition decreases in the order SCN− > NO3− > Br− > OH− > Cl− > F−. Co-ions were found to have a little or no effect on the concentration of pentanol at the end of the transition for a particular salt concentration. The effectiveness of nonelectrolytes in promoting the sphere-rod transition of 2% TTMAB decreases in the order n-hexanol >n-pentanol ∼ benzyl alcohol > 3-methyl1-butanol. n-Hexylamine was found to be less effective than n-pentanol in TTMAB as opposed to previous observations in SDDS. Urea and dioxane were found to retard the sphere-rod transition in TTMAB as in SDDS. Extrapolation of transition concentrations of 2% TTMAB and 3.5% SDDS containing cosurfactants (n-pentanol, n-hexanol, n-hexylamine) and salts to zero concentration of cosurfactants gives the threshold salt concentrations. Rodlike micelles are formed above the threshold salt concentrations, which are 0.171 ± 0.005 M NaBr at 25°C and 0.286 ± 0.010 M NaBr at 45°C in 2% TTMAB, and 0.438 ± 0.009 M NaCl at 25°C and 0.582 ± 0.014 M NaCl at 45°C in 3.5% SDDS.

A lamellar liquid crystal (LC) intrudes into a main miscibility gap and forms a three-phase triangle in a water/sodium octyl sulfonate (R 8 SO 3 Na)/hexanol system at lower temperatures. Upon addition of isooctane, the LC phase retreats to a concentrate region and a critical point is produced in an alcoholrich region. Then, another three-phase triangle containing the LC is formed at the critical endpoint. Upon further addition of isooctane, both three-phase triangles are merged and the isotropic phase (microemulsion) is continuously connected from water- to alcohol- (or oil-) rich regions. This phase behavior is essentially analogous to that in the ternary water/R 8 SO 3 Na/hexanol system as a function of temperature at constant pressure. Thus, isooctane unstabilizes the LC and reduces the intrusion temperature (IT) at which the LC intrudes into the main miscibility gap. This phenomenon is related to the formation of microemulsions. At higher temperatures above the IT, there is a critical point in the main miscibility gap in the ternary system without oil. Upon addition of isooctane, the critical point is moved to an alcohol-rich region. Accordingly, an ionic surfactant tends to be more soluble in water in the presence of oil.

Ag nanoparticles (NPs) of approximately 2.5 ± 0.6 nm in size with high stability were prepared on montmorillonite clay in n-hexanol ([Ag NP/clay]). The aqueous suspensions of Ag NP/clay obtained were colored pale yellow to gray, and an intense yellow surface plasmon band was observed at approximately 397–422 nm at a [Ag + ] concentration of 0.01–1 M. Fluorescence peaks of these Ag NP/clay suspensions, which were due to interband transitions of Ag NPs, were observed at approximately 447 nm upon excitation at approximately 341 nm. Photoinduced charge separation and electron accumulation in the presence of 2-propanol were observed in the Ag NPs on the clay. The photogenerated holes indicate a reaction with OH − because the generation of OH radicals decreased in the presence of 2-propanol, as observed using a spin-trapping electron spin resonance (ESR) method. The amount of H 2 produced depended on the amount of Ag NPs on the clay and the concentration of 2-propanol in the suspension. Antibacterial activity of Ag NPs on clay was also observed against Escherichia coli even after 12 years. This simple method of preparation in n-hexanol led to the successful formation of highly stable and photoactive Ag NPs on montmorillonite clay.

Aqueous solutions of alkyldimethylamine oxides (CnDAO, n = 14, 16, 18, hexadecenesuccinic acid (C16SA), and diglycerol isostearyl ether (C18DGE) were observed with the video-enhanced differential interference contrast microscope (VEM). Flat plate-like assemblies were seen in iridescent solutions of C16DAO and C18DAO, while globular vesicle-like assemblies were formed in iridescent solutions of C14DAO mixed with hexanol and decane, C16SA, and C18DGE. Similar assemblies were also observed in the dilutions of iridescent solutions which displayed no iridescence. Whereas plate-like assemblies of C16DAO disappeared above 30°C, assemblies of C18DAO changed above 50°C from plate-like to globular. The relation of the iridescence to the molecular assemblies in surfactant solutions is discussed.

In the synthesis of anionic-surfactant-templated mesoporous silica (AMS), the effects of alcohols have been investigated for the first time. Without the addition of extra alcohols, spherical mesoporous silica with radially oriented mesopores could be obtained through the anionic surfactant templating route. By using alcohols with different carbon chain length such as ethanol, n-butanol, hexanol and 1-octanol as the additives, different morphologies and mesostructures of mesoporous silica were obtained. It was found that both the types and concentrations of alcohols in the synthesis solution could tune the morphologies and mesostructures of the AMS, giving rise to the formation of hexagonal mesoporous discs and particles with novel multi-layered inner structure. In general alcohol with appropriate carbon chain length such as n-butanol and hexanol could act as the co-surfactant in the synthesis of mesoporous silica templated by anionic surfactant.

The critical reverse micelle concentrations of C 12 - s -C 12 ⋅2Br ( s = 2 , 3 , 4 , 5 , 6 , 8 , 12 ) in n -heptane/ n -hexanol solutions, cmc I s , have been determined by absorption spectrum method using iodine as probe. The values of cmc I s are smaller than those of the critical micelle concentrations (cmc aq s ) in aqueous solution and reach a maximum at s = 4 , which is similar to the variation of cmc aq with s . The variation of cmc I with s is attributed to the alteration in the spacer chain conformation, i.e. when the spacer is short enough, it may adopt stretch configuration and when the spacer is long, it tends to bend towards the continuous oil phase to achieve a more densely packing of the quaternary ammonium heads on the surface of the core.

Sorbitan trioleate (Span 85) modified with Cibacron Blue F-3GA (CB) was used as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. It was found that the addition of hexanol to the reversed micellar system resulted in a significant increase in water content and hydrodynamic radius of the affinity-based reversed micelles. Moreover, the reversed micelles with hexanol revealed broader aggregation number distribution and larger average aggregation number than the reversed micelles without hexanol addition. This is considered to be due to the decreases in the micellar curvature and rigidity of the micellar interfacial layer and the increase in the micellar interfacial fluidity. Consequently, the solubilization capacity of lysozyme increased about 70% in the reversed micellar solution with 3 vol% hexanol. On the other hand, the capacity of BSA was only 30% increased under the same conditions due to its larger molecular size than lysozyme. Kinetic analysis revealed that the increase in the micellar interfacial fluidity in the presence of hexanol resulted in faster release of lysozyme from the micelles, thus leading to an increase of the overall volumetric mass transfer coefficient in the back extraction.

Miscibility of hexanol and dodecylammonium chloride (DAC) in adsorbed films and micelles was investigated by evaluating the compositions of the adsorbed films and micelles from surface tension measurements. Judging from the phase diagram of adsorption, negative azeotropy of adsorption was observed for the mixed adsorption of hexanol and DAC at water/air interfaces. The nonideal mixing in the adsorbed film was clarified using excess functions of adsorption. Interaction between hexanol and DAC in the adsorbed film was compared with that between other alkanols and surfactants. It was found that the range of azeotropes is narrower for the hexanol–DAC mixture than for the heptanol–octylsulfinylethanol mixture, because interaction between different species in an adsorbed film is weaker in the former than in the latter.

The effects of addition of alkanols (ethanol, n-hexanol, and 3-ethyl-3-pentanol) on the micropolarity and microviscosity of the head group region in reverse micelles of AOT–heptane–water have been investigated by fluorescence probing methods (ANS fluorescence yield and TMADPH fluorescence anisotropy), complemented by the use of the solvatochromic probe ET(30) in absorption spectroscopy. For all the alkanols considered, ANS fluorescence in AOT reverse micelles (at W=3) is quenched by additive incorporation, being the effect elicited almost independent of the alkanol chain length and topology. As sensed by the ET(30) parameter, the micropolarity of the micelle surface increases, remains unmodified, and decreases upon addition of ethanol, 3-ethyl-3-pentanol, and hexanol, respectively. While ethanol barely modifies the fluorescence anisotropy of TMADPH, 3-ethyl-3-pentanol and n-hexanol addition strongly decrease it. The similarity of the tendencies of ANS data to TMADPH anisotropies and the differences between ANS data and ET(30) values would indicate that, at least for 3-ethyl-3-pentanol and n-hexanol, microviscosity, rather than micropolarity, must be considered to interpret the effect of the alkanols upon the fluorescent behavior of ANS.

Magnesium orthophosphates have lately been examined as catalysts for various organic processes. In this work, we studied many compounds of this type synthesized under widely variable conditions, particularly as regards the magnesium and phosphorus sources, precipitant, and gel treatment used. The structure, composition and surface properties of each solid were found to depend on the synthetic procedure used. Thus, freshly made gels consisted largely of MgHPO(4). 3H(2)O, Mg(3)(PO(4))(2). 8H(2)O, or Mg(3)(PO(4))(2). 22H(2)O. The latter two can be interconverted by using various treatments. Calcination of the most extensively hydrated gel produces catalysts of increased specific surface area, acidity, and basicity. Thermal treatment yields phases such as Mg(2)P(2)O(7), Mg(3)(PO(4))(2), and NaMg(4)(PO(4))(3). The activity and selectivity exhibited by these solids in the conversion of gaseous 2-hexanol vary enormously with the particular synthetic procedure. In addition to surface properties, the structure and composition of the catalysts-particularly their sodium content-appear to play essential roles in their catalytic behavior, which is seemingly determined by their previously suggested dehydrogenating ability (with formation of sodium-magnesium mixed phosphates). Copyright 1999 Academic Press.

The effect of strength of attraction and volume fraction on the mechanical properties of alumina particle networks were investigated. Alumina particle gels were formed reversibly and in situ in the rheometer by cooling alumina particle suspensions with adsorbed poly(12-hydroxy stearic acid) suspended in a marginal solvent, hexanol. The collapse of the polymer layer with decreasing solvency (temperature) induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. The gelation temperature depends on volume fraction. At the gel temperature, Tgel, the gel becomes predominantly elastic; at temperatures below Tgel, the elasticity increases with decreasing temperature. We find that the elastic modulus data, measured over a wide range of volume fraction (0.2phi;0.425) and temperature (10-14 degreesC), follows: G = G0(phi; -phi;g)s. This scaling suggests the prefactor and exponent to be independent of temperature. We present some arguments for why subjecting a particle gel to a preshear procedure might result in an temperature-dependent prefactor. By invoking such an effect, we are able to rescale and collapse previously published moduli data on presheared suspensions according to the (phi; -phi;g) expression. Copyright 1999 Academic Press.

The reactions, oxidation of iodide by persulfate and basic hydrolysis of crystal violet, were investigated in the w/o microemulsion formed by sodium dodecyl sulfate, water, and hexanol. The second order rate constants were measured as a function of water to surfactant molar ratio and hexanol content. The increased rates were attributed to the smaller droplet size of the water pools. The rates are shown to be controlled by the water content as well as the hexanol content. It is shown that the manner in which the rate is affected applies to the catalyzed as well as the retarded reactions. This system is shown to be more effective than the AOT/water/decane system.

The solubilization capacity of water/oil microemulsions formed with fatty acid soaps and alcohols was studied as a function of alkyl chain length of oil (C8 to C16), soap (C14 and C18), and alcohol (C4 to C7). For n-butanol with both soaps, the maximum amount of water solubilized in the microemulsion continuously decreased with increasing oil chain length whereas for n-heptanol the solubilization capacity continuously increased. For pentanol with both soaps and for hexanol with sodium stearate, the solubilization reached a maximum when the oil chain length, lo, plus that of the alcohol, la, was equal to that of the surfactant, ls, (i.e., la + lo = ls). When excess water was added to these systems, a birefringent aqueous phase in equilibrium with an isotropic upper phase formed if la + lo < ls whereas a different phase behavior, namely, the formation of two isotropic phases, was observed if la + lo ⩾ ls. Both of these observations indicate a chain length compatibility effect similar to that observed in monolayers, foams, emulsions, and lubricants. The solubilization behavior is interpreted in terms of partitioning of alcohol among oil, water, and the interface depending upon the chain length of oil and alcohol, as well as in terms of molecular packing at the interface in relation to the disorder produced by the chain length compatibility effect. It was concluded from the oil-alcohol titration study that the molar ratio of alcohol to soap at the interface increases with oil chain length. We propose that the increase in the alcohol/soap molar ratio leads to increased spacing between carboxyl groups resulting in a greater degree of ionization. Electrical resistance and dielectric constant measurements yielded results consistent with this interpretation. At a given water/oil ratio, the electrical resistance of microemulsions decreases, the dielectric constant increases, and the thickness of ionic atmosphere within the water droplets increases as the oil chain length is increased. These phenomena are consistent with the concept that microemulsions form, and vary their structure, under the influence of surfactant and alcohol partitioning between aqueous and oleic phases and the consequent interfacial activity of both species. Here, the partitioning of alcohol and soap is subtly varied by changing the oil chain length.

Samples of natural Brazilian quartz were variously covered with dodecylamine chloride (DDACl) from methanolic solutions. Then they were subjected to flotation tests and ζ potential measurements in doubly distilled water. In the second series of experiments the samples covered with DDACl were then covered with known amounts of n -hexane or n -hexanol and ζ potentials were determined. From this relationship dispersion and polar components of surface free energy of the quartz samples were calculated. The results obtained allow us to conclude that already at 0.25 statistical monolayer of DDACl the sample of quartz floats in 90%, which is connected with drastic reduction of the polar component of quartz surface free energy from 115 mJ/m 2 (bare surface) to 7.2 mJ/m 2 . The maximum flotation activity appears at one statistical monolayer of the amine, and corresponds to complete reduction of the polar interactions at the quartz-water interface.

Three coexisting liquid phases become identical at a high-order critical point, a tricritical point. This phenomenon was found among water, surfactant, and oil phases in a water/R8SO3Na/hexanol/isooctane system, in which a tricritical line exists at constant pressure (atmospheric pressure). A tricritical temperature increases abruptly with increasing salinity and a three-phase region appears below its tricritical temperature at each salinity. On the other hand, the maximum temperature of liquid crystalline phase goes up with decreasing salinity and finally it coincides with the tricritical temperature at a certain salinity between 0.7 and 0.8 wt%. Therefore, tricritical phenomena cannot be observed below its salinity and below this temperature. The effect of added salt on the solution behavior of an ionic-nonionic mixture is (i) suppression of the formation of liquid crystal, and (ii) an increase in the tricritical temperature. This is the reason why it is generally necessary to add salt for the formation of a three-phase region in an ionic-nonionic surfactant mixture system.

Fluorescence techniques are used to study the effect of size on the properties of dioctadecyldimethylammonium chloride vesicles. The solubilization site and the deactivation rates of excited pyrene by bromide counterions and oxygen are markedly dependent on vesicle size at low temperature and strongly affected by the gel-liquid crystalline phase transition. The results obtained are accounted for by considering the structural differences between large and small vesicles. It is shown that the temperature dependence of the interaction rate between the probe and oxygen can used to monitor the changes in vesicle fluidity accompanying the gel-liquid cystalline phase transition and the sensitivity of the fluidity and phase transition temperature to the incorporation of additives ( n -octanol). The effect of vesicle size upon the capacity to incorporate n -alkanols (from hexanol to nonanol) and carbon tetrachloride was also examined. From the measurement of the partition constants in both vesicles it was found that, at 22°C, the small vesicles are better solvents for all the solutes studied. The solvent capacity of the large vesicles toward heptanol improves with the amount of alkanol incorporated. These results can also be rationalized in terms of the more ordered packing of the large vesicles below the phase transition temperature.

The solubilization of a homologous series of aliphatic n -alcohols and aromatics in sodium perfluorooctanoate (SPFO) micelles and in SPFO/sodium decanoate (SD)-mixed micelles in aqueous solution have been investigated by the Fourier transform NMR Pulsed-Gradient Spin-Echo (PGSE) method. The incremental free-energy change for transfer of a methylene group from the aqueous pseudophase to the micellar pseudophase was determined to be −2.3 kJ mole −1 per methylene group and −2.1 kJ mole −1 per methylene group for the mixed micelle. By comparison with corresponding data for the solubilization process in hydrocarbon micelles, the results can be rationalized in terms of nonideal interactions between hydrocarbons and fluorocarbons.

The effect of polar, nonpolar, and mixed polar-nonpolar additives on the counterion association, the structure, and the size of aqueous sodium dodecyl sulfate micelles has been examined by measuring the conductivity, the viscosity, and the electromotive force at 298.15 K. Octane does not affect the degree of counterion association, but the mobility of the micelles decreases. This is mainly due to an increased micellar volume. Small quantities of 1-butanol and 1-hexanol decrease the degree of counterion association. At higher hexanol molalities larger micellar aggregates, rod- or disk-like micelles are formed. Long-chained α,ω-alkanediols, 1,9-nonanediol and 1,10-decanediol, also reduce the degree of counterion association. The shorter diols apparently affect the micellar system mainly through their effect on the solvent. The effect of the mixed additives is intermediate to that of pure components. Changes in the aggregation number, the micellar radius, and the number of associated counterions have been estimated from the conductivity and electromotive force measurements. Addition of octane does not affect the degree of associated counterions, but the micellar aggregation number increases. Addition of hexanol lowers both the micellar aggregation number and the fraction of associated counterions.

The structural characteristics of three similar systems containing sodium stearate, alcohol (n-pentanol, n-hexanol, or n-heptanol), hexadecane, and varying amounts of water were investigated. The systems were identical in composition except for the nature of alcohol used for producing microemulsions. In all the three microemulsion systems, the microemulsion remained isotropic and clear up to the water/oil ratio of 0.48. However, the electrical resistance studies indicated that the three systems were strikingly dissimilar. Upon increasing the water/oil ratio, n-pentanol microemulsion systems exhibited a constant decrease in resistance; hexanol microemulsion systems showed an initial increase and a subsequent sharp decrease whereas n-heptanol microemulsion systems exhibited very high electrical resistance which could not be measured (>l07Ω-cm). The pentanol microemulsion systems exhibited dielectric relaxation at lower water/oil ratios as compared to the hexanol microemulsion systems. However, heptanol microemulsion systems did not exhibit dielectric relaxation. The dielectric relaxation results were interpreted in terms of ionization of the carboxyl group and the concomitant formation of the electrical double layer. This occurred at lower water/oil ratios in pentanol microemulsion systems as compared to hexanol microemulsion systems. However, there was no measurable ionization or electrical double layer formation in heptanol microemulsion systems. The spin label studies using a stearic acid spin probe suggested that the stearate molecule is located at the oil/water interface. Furthermore, the spin label incorporated in microemulsions exhibited anisotropic behavior in contrast to the isotropic behavior of the spin label dissolved in oil or water. The values of order parameter suggested that the order in interfacial film as measured by the spin label decreased in the following order: heptanol > hexanol > pentanol. In other words, the shorter chain alcohol produced a maximum disorderat the oil/water interface. The isotropic hyperfine splitting constant of the label in the three microemulsion systems suggested that the environment experienced by the spin label was intermediate between that of water and oil. In summary, the electric, dielectric, and ESR measurements suggest that the alcohol chain length affects the ionization, interfacial polarization, and disorder at the oil/water interface which in turn influences the properties of microemulsions.

Phase diagrams have been determined showing the extent of the inverse micellar or microemulsion region for systems consisting of water-surfactant-cosurfactant or water-surfactant-hydrocarbon cosurfactant mixture with three surfactants and four cosurfactants. The surfactants are sodium dodecyl sulfate, sodium laurate, and tetradecyltrimethylammonium bromide while the cosurfactants are pentanol, hexanol, pentylamine, and hexylamine. Hexylamine is found to be a very effective cosurfactant giving rise to very good water solubilizing capacity at extremely low surfactant concentrations and very low cosurfactant levels at rather high initial hydrocarbon levels.