Interfacial composition, thermodynamic properties, and structural parameters of water-in-oil microemulsions stabilized by 1-pentanol and mixed surfactants

The present study is focused on the evaluation of the interfacial composition, thermodynamic properties, and structural parameters of water-in-oil mixed surfactant microemulsions [(cetylpyridinium chloride, CPC+polyoxyethylene (20) cetyl ether, Brij-58 or polyoxyethylene (20) stearyl ether, Brij-78)/1-pentanol/n-heptane, or n-decane] under various physicochemical environments by the Schulman method of cosurfactant titration of the oil/water interface. The estimation of the number of moles of 1-pentanol at the interface (n(a)(i)) and bulk oil (n(a)(o)) and its distribution between these two domains at the threshold level of stability have been emphasized. The thermodynamics of transfer of 1-pentanol from the continuous oil phase to the interface have been evaluated. n(a)(i),n(a)(i), standard Gibbs free energy (ΔG(t)(0)), standard enthalpy (ΔH(t)(0)), and standard entropy (ΔG(t)(0)) of transfer process have been found to be dependent on the molar ratio of water to surfactant (ω), type of nonionic surfactant and its content (X(Brij-58 or Brij-78)), oil and temperature. A correlation between (ΔH(t)(0)) and (ΔS(t)(0)) is examined at different experimental temperatures. Bulk surfactant composition dependent temperature insensitive microemulsions have been reported. Associated structural parameters, such as droplet dimensions and aggregation number of surfactant and cosurfactant at the droplet interface have been evaluated using a mathematical model after suitable modifications for mixed surfactant systems. In light of these parameters, the prospect of using these microemulsion systems for the synthesis of nanoparticles and the modulation of enzyme activity has been discussed. Correlations of the results in terms of the evaluated physicochemical parameters have been attempted.     

Physicochemical investigations of microemulsification of eucalyptus oil and water using mixed surfactants (AOT+Brij-35) and butanol

Microemulsification of a vegetable oil (eucalyptus) with single and mixed surfactants (AOT and Brij-35), cosurfactant of different lipophilicities (isomers of butanol), and water were studied at different surfactant and cosurfactant mixing ratios. The phase diagrams of the quaternary systems were constructed using unfolded and folded tetrahedron, wherein the phase characteristics of different ternary systems can be underlined. The microemulsion zone was found to be dependent upon the mixing ratios of surfactant and cosurfactant; the largest microemulsion zone was formed with 1:1 (w/w) S:CS. The effects of temperature and additives (NaCl, urea, glucose, and bile salts of different concentrations) on the phase behavior were examined. The mixed microemulsion system showed temperature insensitivity, whereas the Brij-35 (single) stabilized system exhibited a smaller microemulsion zone at elevated temperature. NaCl and glucose increased the microemulsion zone up to a certain concentration, beyond which the microemulsion zones were decreased. These additives decreased the microemulsion zones as temperature was increased. The effect of urea on microemulsion zone was found to be insignificant even at the concentration 3.0 mol dm(-3). Little effect on microemulsion zone was shown by NaC (sodium cholate) at 0.25 and 0.5 mol dm(-3) at different temperatures. The conductance of the single (AOT) and mixed microemulsion system (AOT+Brij-35) depends upon the water content and mixing ratios of the surfactants, and a steep rise in conductance was observed at equal weight percentages of oil and water. Viscosities for both single (AOT) and mixed (AOT+Brij-35) surfactant systems passed through maxima at equal oil and water regions showing structural transition. The viscosities for microemulsion systems increased with increasing Brij-35 content in the AOT+Brij-35 blend. Conductances and viscosities of different monophasic compositions in the absence and presence of additives (NaCl and NaC) were measured at different temperatures. The activation energy of conduction (DeltaE(cond)( *)) and the activation enthalpy for viscous flow (DeltaH(vis)( *)) were evaluated. It was found that both DeltaE(cond)( *) and DeltaH(vis)( *) were a function of the nature of the dispersion medium. Considering the phase separation point of maximum solubility, the free energy of dissolution of water or oil (DeltaG(s)(0)) at the microdispersed state in amphiphile medium was estimated and found to be a function of surfactant composition.     

Physicochemical investigations of anionic–nonionic mixed surfactant microemulsions in nonaqueous polar solvents: I. Phase behavior

Phase behaviors of AOT/heptane (Hp)/formamide (FA), ethylene glycol (EG), propylene glycol (PG), triethylene glycol (TEG) and glycerol (GLY) have been investigated in the absence and presence of a nonionic surfactant, polyoxyethylene(2) cetyl ether (Brij-52) at 303 K. The phase characteristics of (AOT+Brij-52)/Hp/(EG or PG or TEG) have been found to be different from that of AOT/Hp/FA systems in respect of both the area of monophasic domain and the appearance of other mesophases. The area of monophasic domain of (AOT+Brij-52)/Hp/EG depends on the content of Brij-52 (X _Brij-52) and shows a maximum at X _Brij-52=0.4. A negligible effect on the area of the monophasic domain has been shown by more hydrophobic surfactants, polyoxyethylene(2) stearyl ether (Brij-72) and polyoxyethylene(2) oleyl ether (Brij-92). The effect of oils (dodecane and hexadecane) on the mixed systems stabilized by (AOT+Brij-52) in EG has been investigated. The area of monophasic domain has been found to be dependent on the type of nonaqueous solvents and follows the order GLY>EG>PG>TG. A systematic investigation on the measurement of phase volumes of mixed surfactant systems [AOT+nonionic surfactant(s)] stabilized in oils of different chain lengths (heptane, dodecane and hexadecane) and polar solvent (EG) has been carried out at different compositions of the ingredients to identify the phase transitions of these systems as a function of X _Brij-52. The threshold point of phase transition (both W I→W IV and W IV→W II transitions) has been found to be a function of the configuration of added nonionic surfactant, nature of the polar solvent and oil. The conversion of the initial oil/EG droplets into EG/oil droplets with increasing X _nonionic has been facilitated for hydrophobic surfactants polyoxyethylene(4) lauryl ether (Brij-30), Brij-52, and Brij-72 in comparison to the hydrophilic surfactants polyoxyethylene(10) cetyl ether (Brij-56) and polyoxyethylene(20) cetyl ether (Brij-58).     

Percolation phenomenon in mixed reverse micelles: the effect of additives

The conductivity of AOT/IPM/water reverse micellar systems as a function of temperature, has been found to be non-percolating at three different concentrations (100, 175 and 250 mM), while the addition of nonionic surfactants [polyoxyethylene(10) cetyl ether (Brij-56) and polyoxyethylene(20) cetyl ether (Brij-58)] to these systems exhibits temperature-induced percolation in conductance in non-percolating AOT/isopropyl myristate (IPM)/water system at constant compositions (i.e., at fixed total surfactant concentration, omega and X(nonionic)). The influence of total surfactant concentration (micellar concentration) on the temperature-induced percolation behaviors of these systems has been investigated. The effect of Brij-58 is more pronounced than that of Brij-56 in inducing percolation. The threshold percolation temperature, Tp has been determined for these systems in presence of additives of different molecular structures, physical parameters and/or interfacial properties. The additives have shown both assisting and resisting effects on the percolation threshold. The additives, bile salt (sodium cholate), urea, formamide, cholesteryl acetate, cholesteryl benzoate, toluene, a triblock copolymer [(EO)13(PO)30(EO)13, Pluronic, PL64], polybutadiene, sucrose esters (sucrose dodecanoates, L-1695 and sucrose monostearate S-1670), formamide distinctively fall in the former category, whereas sodium chloride, cholesteryl palmitate, crown ether, ethylene glycol constitute the latter for both systems. Sucrose dodecanoates (L-595) had almost marginal effect on the process. The observed behavior of these additives on the percolation phenomenon has been explained in terms of critical packing parameter and/or other factors, which influence the texture of the interface and solution properties of the mixed reverse micellar systems. The activation energy, Ep for the percolation process has been evaluated. Ep values for the AOT/Brij-56 systems have been found to be lower than those of AOT/Brij-58 systems. The concentration of additives influence the parameters Tp and Ep for both systems. A preliminary report for the first time on the percolation phenomenon in mixed reverse micelles in presence of additives has been suggested on the basis of these parameters (Tp and Ep).     

Mixed micelles of polyethylene glycol (23) lauryl ether with ionic surfactants studied by proton 1D and 2D NMR

(1)H NMR chemical shift, spin-lattice relaxation time, spin-spin relaxation time, self-diffusion coefficient, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the nonionic-ionic surfactant mixed micelles. Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the ionic surfactants and polyethylene glycol (23) lauryl ether (Brij-35) as the nonionic surfactant. The two systems are both with varying molar ratios of CTAB/Brij-35 (C/B) and SDS/Brij-35 (S/B) ranging from 0.5 to 2, respectively, at a constant concentration of 6 mM for Brij-35 in aqueous solutions. Results give information about the relative arrangement of the surfactant molecules in the mixed micelles. In the former system, the trimethyl groups attached to the polar heads of the CTAB molecules are located between the first oxy-ethylene groups next to the hydrophobic chains of Brij-35 molecules. These oxy-ethylene groups gradually move outward from the hydrophobic core of the mixed micelle with an increase in C/B in the mixed solution. In contrast to the case of the CTAB/Triton X-100 system, the long flexible hydrophilic poly oxy-ethylene chains, which are in the exterior part of the mixed micelles, remain coiled, but looser, surrounding the hydrophobic core. There is almost no variation in conformation of the hydrophilic chains of Brij-35 molecules in the mixed micelles of the SDS/Brij-35 system as the S/B increases. The hydrophobic chains of both CTAB and SDS are co-aggregated with Brij-35, respectively, in their mixed micellar cores.     

Properties of polyethylene glycol (23) lauryl ether with cetyltrimethylammonium bromide in mixed aqueous solutions studied by self-diffusion coefficient NMR

NMR self-diffusion coefficient measurements have been used to study the properties of polyethylene glycol (23) lauryl ether (Brij-35) with cetyltrimethylammonium bromide (CTAB) in the mixed aqueous solutions with different mole fractions of CTAB. By fitting the self-diffusion coefficients to the two-state exchange model, the critical micelle concentrations of the two solutes in the mixed solutions (cmc*1 and cmc*2) were obtained. The critical mixed micelle concentrations (cmc*) were then evaluated by the sum of cmc*1 and cmc*2, which are in good agreement with the results measured by the surface tension method. The cmc* values are lower than those of the ideal case of mixing, which indicates that the behavior of the CTAB/Brij-35 system is nonideal. Moderate interactions between CTAB and Brij-35 in their mixtures can be deduced from the interaction parameters (betaM) based on the cmc* obtained by the NMR self-diffusion method. The compositions (x1) of the mixed micelles at different total surfactant concentrations were also evaluated. By using these results, a possible mechanism of mixed micellar formation and a picture of the formation of nonsimultaneous CTAB/Brij-35 binary mixed micelle were proposed. In contrast to the case of CTAB/TX-100 system, Brij-35 molecules have a tendency to form micelles first at any mole fraction of CTAB. The mixed micellar self-diffusion coefficients (Dm) increase slightly at lower CTAB molar ratios, and then speed up with increasing CTAB mole fraction.     

Interfacial composition, thermodynamic properties and structural parameters of water-in-oil microemulsions stabilized by 1-pentanol and mixed anionic + polyoxyethylene type nonionic surfactants

The interfacial composition $ \left( {n_a^i} \right) $ , thermodynamic properties and structural parameters of the stable water/(SDS + Brij-58 or Brij-78)/1-pentanol/heptane (or decane or isopropyl myristate) have been evaluated under various physicochemical environments by the dilution method. The results showed $ n_a^i $ values increase with increasing water content (ω?=?[water]/[surfactant]) for all the systems, whereas reverse trend was observed for (SDS/Brij-58)/heptane-derived system. The spontaneity of the transfer process of 1-pentanol from bulk oil to the interface $ \left[ { - \Delta G_t^0} \right] $ decreases with increase in ω for all the systems. The effective binding between 1-pentanol and surfactant(s) at the interface follows the order: SDS/Brij-78/IPM < SDS/Brij-58/IPM < SDS/Brij-78/Hp(or, Dc) < SDS/Brij-58/Hp(or, Dc), which corroborates well with the degree of spontaneity of the transfer process. The Gibbs free energy change $ \left( {\Delta G_t^0} \right) $ , standard enthalpy change $ \left( {\Delta H_t^0} \right) $ and standard entropy change $ \left( {\Delta S_t^0} \right) $ have been found to be dependent on ω, type of nonionic surfactant and its content (X_nonionic), oil and temperature, because of the interdependence of the partition equilibrium of Pn between bulk oil and the interface, and strong adsorption of both surfactants at the interface. Synergism in $ \Delta G_t^0 $ and $ \left[ {{{\left( { - \Delta C_P^0} \right)}_t}} \right] $ (standard specific heat change) is evidenced at equimolar composition of SDS and Brij-58 in both oils at all temperatures and advocates more favorable applications for the synthesis of nanoparticles and the modulation of enzyme activity. The radius of water pool (R_w) was very sensitive to the increment of water content and tuned up by the addition of Brijs, which followed the order with decreasing size: IPM < Dc < Hp.     

Phase behavior of the mixtures of poly(oxyethylene) (10) stearyl ether (Brij-76), 1-butanol, isooctane, and mixed polar solvents II. Water and ethylene glycol (EG) or tetraethylene glycol (TEG)

The phase diagrams of the pseudo-quaternary systems poly(oxyethylene) (10) stearyl ether (Brij-76)/1-butanol/isooctane/water (with equal amounts of oil and water in the presence of two nonaqueous polar solvents (NPS), ethylene glycol (EG), and tetraethylene glycol (TEG)), have been constructed at 30 degrees C. Regular fish-tail diagrams were obtained up to psi (weight fraction of EG or TEG in the mixture of polar solvents) equal to 0.5, confirming the establishment of hydrophile-lipophile balance (HLB) of the systems. The maximum solubilization capacity passed through a minimum at psi=0.2. No HLB was obtained at higher psi. The usual fish-tail diagrams were also obtained in temperature-induced phase mapping at fixed W(1) (weight fraction of 1-butanol in total amphiphile). Solubilization capacity and HLB temperature (T(HLB)) decreased with increasing psi at a fixed W(1), the effect being more pronounced for TEG than EG. A correlation between HLB temperature (T(HLB)) and HLB number (N(HLB)) of mixed amphiphiles (Brij-76+Bu) in pseudo-quaternary systems (in the presence of water and partial substitution of water with both NPS) has been established. The novelty of the work with respect to possible applications has been discussed.     

CTAB/正丁醇-正辛烷-水和盐水的拟三元体系相图及微乳液微观结构的电导研究

绘制了CTAB/正丁醇-正辛烷-水和Al(NO₃)3(或Na2WO4)盐水拟三元体系的35℃相图.用电导法并结合电解质理论讨论了微乳液的微观结构,将整个微乳液单相区分为W/O微乳区、O/W微乳区和B.C.双连续区,并且用渗滤理论确定了一个分散相质点为W/O球状结构的反胶团微乳液区.     

两相催化体系中双子表面活性剂对1-十二烯氢甲酰化反应的促进作用

报道了水溶性铑膦配合物组成的复合催化体系催化1-十二烯氢甲酰化反应中,双子表面活性剂[二溴化-(N,N,N′,N′-四甲基)-N,N′-二(十六烷基)-乙二铵]形成胶束的助催化作用.结果表明,在水/有机两相中,双子表面活性剂比单链表面活性剂CTAB具有更好加速催化反应的作用,并使烯烃氢甲酰化的区域选择性显著提高.这归因于双子表面活性剂有较低的cmc,可形成更加紧密规整的胶束结构,有利于增溶在胶束中的烯烃与铑催化剂配位和生成正构醛.     

Phase behavior of monoglycerol fatty acid esters in nonpolar oils: reverse rodlike micelles at elevated temperatures

We have studied nonaqueous phase behavior and self-assemblies of monoglycerol fatty acid esters having different alkyl chain lengths in different nonpolar oils, namely, liquid paraffin (LP 70), squalane, and squalene. At lower temperatures, oil and solid surfactants do not mix at all compositions of mixing. Upon an increase in the temperature of the surfactant system, the solid melts to give isotropic single or two-liquid phases, depending on the nature of the oil and the surfactant. All monolaurin/oil systems form an isotropic single-phase liquid, but with a decreasing alkyl chain length of surfactant, they become less lipophilic and immiscible in oils. As a result, a two-phase domain is observed in the oil rich region of all monocaprylin/oil systems over a wide range of concentrations. Judging from the phase diagrams, the surfactants are the least miscible with squalane, and the order of miscibility tendency is squalene > LP 70 > squalane. With a further increase of temperature, the solubility of the surfactant in the oil increases, and the two-liquid phase transforms to an isotropic single phase. This phase transformation corresponds to the reverse of the cloud-point phenomenon observed in aqueous nonionic surfactant systems. Small-angle X-ray scattering (SAXS) measurements show the presence of reversed rodlike micelles in the isotropic single phase, and the length of the aggregates decreases with increasing temperature and increasing alkyl chain length of the surfactant. These results indicate a rod-sphere transformation with increasing lipophilicity of the surfactant and confirms the validity of Ninham's penetration model in the reversed system. An addition of a small amount of water dramatically enhances the elongation of the reverse micelles. Increasing the surfactant concentration or changing the oil from squalene to LP 70 also increases the length of the rodlike aggregates.     

Effect of temperature and salt on the phase behavior of nonionic and mixed nonionic-ionic microemulsions with fish-tail diagrams

The phase behavior of Brij-56/1-butanol/n-heptane/water is investigated at 30 degrees C with alpha [weight fraction of oil in (oil+water)]=0.5, wherein a 2-->3-->2 phase transition occurs with increasing W1 (weight fraction of 1-butanol in total amphiphile) at low X (weight fraction of both the amphiphiles in the mixture) and a 2-->1-->2 phase transition occurs at higher X. Addition of an ionic surfactant, sodium dodecylbenzene sulfonate, destroys the three-phase body and decreases the solubilization capacity of the system at different delta (weight fraction of ionic surfactant in total surfactant). A three-phase body appears at alpha=0.25, but not at alpha=0.75 for the single system. No three-phase body appears with the mixed system at either alpha value. Increased temperature increases the solubilization capacity of the Brij-56 system; on the other hand, a negligible effect of temperature on the Brij-56/SDBS mixed system has been observed. Addition of salt (NaCl) produces a three-phase body for both single and mixed systems and increases their solubilization capacities. The monomeric solubility of 1-butanol in oil (S1) and at the interface (S1s) has been calculated using the equation hydrophile-lipophile balance plane for both singles- and mixed-surfactant systems. These parameters have been utilized to explain the increase in solubilization capacity of these systems in the presence of NaCl.     

Coexisting lamellar phases in water-oil-surfactant systems induced by the addition of an amphiphilic block copolymer

We report here a pioneering study using quadrupolar splitting NMR to detect new phases and phase compositions in the quasi-ternary microemulsion system water-decane-C(10)E(4)/PEP5-PEO5. The striking observation is that at certain compositions the polymer is apparently no longer incorporated into the membranes of the lamellar phase due to space restrictions. The polymer therefore induces a phase separation into two different lamellar phases L(alpha)(1) and L(alpha)(2) such that it fits into L(alpha)(1) while the excess surfactant forms a polymer-free L(alpha)(2) phase.     

Interface of AOT/Brij mixed reverse micellar systems: conductometric and spectrophotometric investigations

Solubilization and conductivity studies are carried out with AOT/Brijs (Brij-30, Brij-35, Brij-52, Brij-56, Brij-58, Brij-72, Brij-76, Brij-78)/isooctane/water mixed reverse micellar systems. Replacement of AOT molecules with large head group Brij molecules (Brij-30, Brij-35, Brij-56, Brij-58, Brij-76, Brij-78) decreases the solubilization capacity, whereas those with smaller polar head groups (Brij-52 and Brij-72) increases it. The former blends assist the conductance percolation whereas the latter retard it. An attempt has been taken to obtain more insight on the interfacial composition of the mixed interface with the help of spectrophotometric studies using 7-hydroxycoumarin as the fluorophore. The results obtained from the solubilization and conductometric studies have been correlated with those obtained from the spectroscopic studies.     

Studies on the adsorption of Brij-35 and CTAB at the coal-water interface

The adsorption behavior of polyoxyethylene (23) lauryl ether (Brij-35) and cetyl trimethyl ammonium bromide (CTAB) on coal sample has been studied. The adsorption process is found to be sensitive to pH, temperature, electrolyte concentration, and the amount of surface active agent. An attempt has been made to explain the adsorption behavior of the surfactants using the Langmuir equation. The extent of adsorption of Brij-35 on coal is found to be the highest at pH 2, which decreases with increase in pH and remains constant in the neutral and alkaline pH regions. But, the adsorption of CTAB exhibits the opposite behavior of that of Brij-35. Adsorption of any of the surfactant at the coal/water interface sharply decreases the apparent viscosity of 55 wt% coal-water slurry (CWS) at a shear rate of 100 s(-1). Electrostatic adsorption of the surfactants on the coal surface decreases the surface charge and renders the coal surface hydrophobic which is manifested in the form of high apparent viscosity of the coal-water slurry under the test conditions.     

Use of the ternary phase diagram of a mixed cationic/glucopyranoside surfactant system to predict mesostructured silica synthesis

Mixed surfactant systems have the potential to impart controlled combinations of functionality and pore structure to mesoporous metal oxides. Here, we combine a functional glucopyranoside surfactant with a cationic surfactant that readily forms liquid crystalline mesophases. The phase diagram for the ternary system CTAB/H(2)O/n-octyl-beta-D-glucopyranoside (C(8)G(1)) at 50 degrees C is measured using polarized optical microscopy. At this temperature, the binary C(8)G(1)/H(2)O system forms disordered micellar solutions up to 72 wt% C(8)G(1), and there is no hexagonal phase. With the addition of CTAB, we identify a large area of hexagonal phase, as well as cubic, lamellar and solid surfactant phases. The ternary phase diagram is used to predict the synthesis of thick mesoporous silica films via a direct liquid crystal templating technique. By changing the relative concentration of mixed surfactants as well as inorganic precursor species, surfactant/silica mesostructured thick films can be synthesized with variable glucopyranoside content, and with 2D hexagonal, cubic and lamellar structures. The domains over which different mesophases are prepared correspond well with those of the ternary phase diagram if the hydrophilic inorganic species is assumed to act as an equivalent volume of water.     

X-ray reflectivity and interfacial tension study of the structure and phase behavior of the interface between water and mixed surfactant solutions of CH3(CH2)19OH and CF3(CF2)7(CH2)2OH in hexane

The interface between water and mixed surfactant solutions of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH in hexane was studied with interfacial tension and X-ray reflectivity measurements. Measurements of the tension as a function of temperature for a range of total bulk surfactant concentrations and for three different values of the molal ratio of fluorinated to total surfactant concentration (0.25, 0.28, and 0.5) determined that the interface can be in three different monolayer phases. The interfacial excess entropy determined for these phases suggests that two of the phases are condensed single surfactant monolayers of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH. By studying four different compositions as a function of temperature, X-ray reflectivity was used to determine the structure of these monolayers in all three phases at the liquid-liquid interface. The X-ray reflectivity measurements were analyzed with a layer model to determine the electron density and thickness of the headgroup and tailgroup layers. The reflectivity demonstrates that phases 1 and 2 correspond to an interface fully covered by only one of the surfactants (liquid monolayer of CH(3)(CH(2))(19)OH in phase 1 and a solid condensed monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH in phase 2). This was determined by analysis of the electron density profile as well as by direct comparison to reflectivity studies of the liquid-liquid interface in systems containing only one of the surfactants (plus hexane and water). The liquid monolayer of CH(3)(CH(2))(19)OH undergoes a transition to the solid monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH with increasing temperature. Phase 3 and the transition regions between phases 1 and 2 consist of a mixed monolayer at the interface that contains domains of the two surfactants. In phase 3 the interface also contains gaseous regions that occupy progressively more of the interface as the temperature is increased. The reflectivity determined the coverage of the surfactant domains at the interface. A simple model is presented that predicts the basic features of the domain coverage as a function of temperature for the mixed surfactant system from the behavior of the single surfactant systems.     

Dilution method study on the interfacial composition, thermodynamic properties and structural parameters of W/O microemulsions stabilized by 1-pentanol and surfactants in absence and presence of sodium chloride

The phase behaviors, interfacial composition, thermodynamic properties and structural characteristics of water-in-oil microemulsions under varied molar ratio of water to surfactant (omega) at 303 K and also by varying temperatures at a fixed omega(=40) by mixing with 1-pentanol and decane or dodecane in absence and presence of sodium chloride have been studied by the method of dilution. The surfactants used were cetyl pyridinium chloride (CPC), sodium dodecyl sulfate (SDS) and polyoxyethylene (23) lauryl ether (Brij-35). The compositions of 1-pentanol and the surfactant at the interfacial region, the distribution of 1-pentanol between the interfacial region and the continuous oil phase, and the effective packing parameter (P(eff)) at the threshold level of stability have been estimated. The thermodynamics of transfer of 1-pentanol from the continuous oil phase to the interface have been evaluated. The structural parameters viz. radii of the droplet (R(e)) and the waterpool (R(w)), effective thickness of the interfacial layer (d(I)), average aggregation numbers of surfactants (N (s)) and the cosurfactant (1-pentanol) (N (a)) and the number of droplets (N(d)) have also been estimated. The prospect of using these w/o microemulsions for the synthesis of nanoparticles with small size, have been discussed in the light of the radii of the droplet, and waterpool, the extent of variation of effective thickness of the droplet under varied molar ratio of water to surfactant and temperature. An attempt has been made to rationalize the results in a comprehensive manner.     

Effect of hydrophilic groups of Ca surfactants and hydrophobic chains of C(n)DMAO on coordinated vesicle formation

The effects of hydrophilic headgroups of Ca surfactants, calcium dodecylsulfate (Ca(DS)(2)), calcium dodecylsulfonate (Ca(DSA)(2)), and calcium laurate (CaL(2)) and hydrophobic chains of alkyldimethylamine oxide (C(n)DMAO, n = 12, 14, 16) on the formation of Ca(2+)-ligand coordinated vesicles was investigated in detail. On the basis of phase behavior studies, rheological properties and freeze-fracture transmission electron microscope (FF-TEM) images were measured. Quite different phase behaviors were observed in different surfactant systems. For a Ca surfactant with a highly polar group, Ca(DS)(2), vesicles were observed in all Ca(DS)(2)/C(n)DMAO (n = 12, 14, and 16) systems, whereas for Ca surfactant with lower polar group, Ca(DSA)(2), vesicles can form in Ca(DSA)(2)/C(n)DMAO systems of n = 14 and 16 but not for n = 12. For CaL(2), the surfactant with the least polar group, vesicles form only in the CaL(2)/C(16)DMAO system. The results demonstrate that in the systems formed by Ca surfactants and C(n)DMAO, the formation of vesicles is driven not only by interaction between Ca(2+) and the N → O groups of C(n)DMAO but also by electrostatic and hydrophobic interactions. Vesicles prefer to form in Ca surfactants with highly polar headgroups and C(n)DMAO with long chain length.     

Evolution of packing parameters in the structural changes of silica mesoporous crystals: cage-type, 2D cylindrical, bicontinuous diamond and gyroid, and lamellar

Cage-type, two-dimensional (2D) cylindrical hexagonal (C), bicontinuous diamond (D), bicontinuous gyroid (G), and one-dimensional (1D) lamellar (L) structures of silica mesoporous crystals (SMCs) were obtained by using the anionic surfactant N-stearoyl-l-glutamic acid (C(18)GluA) as a template in the presence of the nonionic surfactant C(16)(EO)(10) (Brij-56). The mesostructures were controlled by the organic/inorganic interface curvature change induced by Brij-56. A synthesis-field diagram showed that the mesostructure changed in the sequence cage-type → C → intergrowth of C and D → intergrowth of C and G → D → G → L with increase of the amount of Brij-56. Mixed micelles were formed by the anionic and nonionic surfactants, the packing parameter g of which increased with increasing the addition amount of nonionic surfactant and the reaction temperature. The local g parameter was obtained from electron crystallography reconstruction results by calculating mean curvatures and Gaussian curvatures from the equi-electrostatic potential surface. The intergrowth of C and D and two kinds of intergrowth of C and G are also discussed.