Studies in the phase behavior of the microemulsions formed by mixed cationic and nonionic surfactants

The middle-phase behavior for the systems of cetyltrimethylammonium bromide (CTAB)/poly-ethyleneglycol-9-monododecyl ether (AEO₉)/alcohol/oil/brine and CTAB/octylphenolpolyoxyethylene-10-ether (Triton X-100)/alcohol/oil/brine have been studied with ɛ-β fishlike phase diagram method. The interfacial layer composition was determined, and some significant physicochemical parameters are derived from the hydrophilic-lipophilic balance plane equation. The effects of different alcohols, oils, temperature and inorganic salt (NaCl) on the middle-phase behavior of microemulsion formed by composite CTAB/AEO₉ systems were also investigated systematically. The effects of different factors on the phase behavior of microemulsions formed by CTAB/AEO₉ and CTAB/TX-100 systems were compared. The results suggest that the solubilization of CTAB/AEO₉ microemulsion is higher than that of CTAB/TX-100 system under the same conditions.     

Phase behaviour and microstructures of microemulsions (I)

By the orthogonal design, the optimal formation conditions for the middle-phase microemulsions in the system dioctadecyldimethylammonium chloride (DODMAC)/ sodium dodecyl sulfate (SDS)/n-butanol/n-hep-tane/brine were obtained as follows: W_DODMAC: W_SDS = 1:4-1:5,C _π-butanol (%) = 11.0-12.0, andC _NaCl (%) = 3.25 Investigations have been made on the effects of the concentrations of NaCl and n-butanol (l.0%-14.0%), the ratios ofWDODMAC: to W_SDS, and the kinds of alcohols (n-propanol, n-butanol, and n-pentanol) on the formation, the phase behaviour, the ultralow interfacial tensions, the optimal salinity (S^*), and the length of salinity (δS). Some rules and data were worked out about the formation and characteristics of the middle-phase microemulsions. The mi-crostructures of the middle-phase microemulsions were also studied by using FT-IR, ESR, and freeze fracture electron microscopy techniques. The results from the three methods show that the microstructures of the middlephase mi-croemulsions undergo the change from O/W to bicontinuous (B.C.) and to W/O. The distribution rule of the orga-nized molecule assemblies in the middle-phase microemulsions is conducible to constructing the model of microemulsion systems, to recognizing the microstructures of the middle-phase microemulsions, and to setting forth the relationship between the microstructures and macro-properties of rnicroemulsions. Project supported by the Niltional Natural Science Foundation of China and the Chinese Postdoctoral Science Foundation.     

Interaction of Diquat and Paraquat with Glutathione Studied by Means of Charge-Transfer Chromatography

Abstract

The interaction of reduced and oxidized glutathiones with the herbicides diquat and paraquat was studied by charge-transfer chromatography carried out on un-impregnated cellulose layers. Diquat and paraquat interact both with reduced and oxidized glutathiones forming charge-transfer complexes. The interaction is of hydrophilic character in both cases. The formation of covalently bonded conjugates was not observed. The strength of interaction decreases in ionic (LiCl, NaCl, KCl, MgCl₂ and CaCl₂) environment in the case of oxidized glutathione. The charge of cation had a higher impact on the strength of interaction than that of the hydrated ion radii.     

Studies on the middle-phase microemulsion of lauric-<Emphasis Type="Italic">N</Emphasis>-methylglucamide

The middle-phase behavior and the solubilization power of the lauric-N-methylglucamide/alcohol/alkane/water quaternary system are studied. A series of phase inversions of Winsor Type I (2) → III (3) → II ( ) emulsions are observed from the fishlike phase diagram. The compositions of the hydrophilic-lipophilic balanced interfacial layer in the middle of the middle-phase are calculated by the HLB plane equation. The effects of different alkanes, alcohols, and the concentration of an NaCl solution on the phase behavior and solubilization power are investigated, which indicates that alkanes with short hydrocarbon chains and alcohols with long alkyl chains have large solubilization power. The concentration of NaCl solution has a small influence on the solubilization power, whereas, the larger the NaCl concentration, the smaller the weight fraction of alcohol needed to balance the hydrophilic-lipophilic layer. The text was submitted by the authors in English.     

Effects of isomeric alcohols on the phase behavior and solubilization of the microemulsion systems formed by anionic surfactants

The middle-phase ɛ-β fishlike phase diagrams of the pseudoquaternary microemulsion systems sodium dodecyl sulfate (sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate)/1-butanol (2-butanol, t-butanol)/n-octane/brine (5% NaCl) were plotted. The effect of three isomeric alcohols (1-butanol, 2-butanol, and t-butanol) on the phase behavior and solubilization was investigated. From the ɛ-β fishlike phase diagram, the composition of the interfacial layer, the solubilities of alcohols and the solubilization ability (the solubility parameter SP*, and the middle-phase volume fraction ϕ) of the microemulsion systems were calculated and discussed. The alcohol content in the interfacial layer and the solubilities of alcohols are in the order: 1-butanol < 2-butanol < t-butanol, but the solubilization ability is in the inverse order.     

Middle-phase microemulsions of green surfactant alkyl polyglucosides

Microemulsions are important organized molecular assembles in surfactant solutions and are used in various fields such as tertiary oil recovery, pharmaceutics, cosmetics, nanoparticle synthe-sis and chemical engineering. The more commonly used nonionic surfactants to produce micro- emulsions are the ethylene oxide-based compounds (CiEj). In recent years alkyl polyglucosides have been received considerable attention in producing microemulsions[17]. Alkyl polyglucosides (APG), which are widely…     

Phase behaviour and microstructures of microemulsions(Ⅰ)

By the orthogonal design,the optimal formation conditions for the middle-phase microemulsions in the system dioctadeeyldimethylammornum chloride (DODMAC)/ sodium dodecyl sulfate (SDS)/n-butanol/n-hep-ane/brine were obtained as follows.Investigations have been made on the effects of the concentrations of NaCl and n-butanol(1.0%-14.0%),the rantos of W to Wshs and the kinds of alcohols (n-propanol,n-butanol,and n-pentanol) on the formation,the phase behavtour,the ultralow interfacial tensions,the optimal salinity (S*),and the length of salinity (S).Some rules and data were worked out about the formation and characteristics of the middle-phase microemulsions.The mi-crostruenres of the middle-phase microemulsions were also studied by using FT-IR,ESR,and freeze fracture electron microscopy techmques The results from the three methods show that the microstructures of the middle-phase mi-croemnlsions undergo the change from O/W to bicontinuous(B C.) and to W/O.The distribution rule of the orga-mzed molecule ass     

Effect of hydrophobically modified polymer on salt-induced structural transition in microemulsions

The phase boundaries of the middle-phase microemulsion for NaCl/SDS/H2O/1-heptane/1-pentanol systems in the absence of polymer and in the presence of unmodified poly(acrylamide) (PAM) and hydrophobically modified poly(acrylamide) (HMPAM) have been determined at varying salt concentrations. These three middle-phase microemulsions (with HMPAM, with PAM, and without polymer) were studied using interfacial tension measurement, steady-state fluorescence, and time-resolved fluorescence quenching. Compared to the polymer-free system and the system with PAM, the addition of HMPAM significantly enlarges the range of the salt concentrations for the formation of the middle-phase microemulison and causes both the excess oil and aqueous phases to increase in volume at the expense of the middle-phase microemulsion. For the middle-phase microemulsion with HMPAM, the interfacial tensions of the microemulsion phase with the excess oil phase and with the excess aqueous phase are all ultralow and exhibit higher values than those with PAM and without polymer. At the same salt concentration, the apparent surfactant aggregation number in the middle-phase microemulsion with HMPAM has the smallest value among these three systems. All results indicate that the strong interaction of surfactant with hydrophobically modified polymer has a large effect on the formation and properties of the middle-phase microemulsion.     

Mono- and Di-valent Salts as Modifiers of PEO-PPO-PEO Block Copolymer Interactions with Silica Nanoparticles in Aqueous Dispersions

Colloidal stabilization of nanoparticle dispersions is central to applications including coatings, mineral extraction, and dispersion of oil spills in oceanic environments, which often involves oil-mineral-aggregates (OMAs). We have an ongoing interest in the modulation of amphiphile micellization and adsorption behavior in aqueous colloidal dispersions in the presence of various additives. Here we evaluate the effect of added salts CaCl₂, MgCl₂, and NaCl on the micellization and adsorption behavior of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer Pluronic P105 (EO₃₇PO₅₆EO₃₇). In 0.10 wt% silica nanoparticle (10.6 nm average diameter) dispersion, adsorbed block copolymer layer formation begins at a critical surface micelle concentration (csmc) of 0.02 wt%, well below the critical micellization concentration of Pluronic P105 in water. Dye solubilization experiments demonstrate an increase in the csmc upon addition of each salt. Each added salt reaches a level of maximum effectiveness in its ability to disfavor Pluronic P105 adsorption at the silica surface. These peak levels occur at concentrations of 0.005, 0.03, and 0.05 M for CaCl₂, MgCl₂, and NaCl, respectively, in the presence of 0.10 wt% silica nanoparticles. We explain these results in the context of an electrostatic displacer mechanism and discuss possible connections to OMA-dispersant formation.     

Solutions of alkali soaps and water in fatty acid V. Measurements of water vapour pressure and electrical conductivity

Measurements of water pressure and electrical conductivity have contributed to show that the extended, isotropic liquid L₂-phase region in the system sodium octanoate/ octanoic acid/water may be divided into several subregions, inside which the character of the system is different. In the non-aqueous part of the phase and at low contents of water and more than about three moles of octanoic acid per mole of sodium octanoate the character is that of a solution of acid sodium octanoate in octanoic acid. At high water contents the L₂-phase has the character of a solution of acid sodium octanoate in water. Intermediately there is a large region where the character of the phase is reminiscent of a hydrated acid sodium octanoate in fluid state. In this region the content of octanoic acid is below three moles per mole of sodium octanoate and the maximal water content is about that bound to the polar groups.In the intermediate region the water vapour pressure is regulated mainly by the extent and type of the bonding of the water to the polar groups, and the electrical conductivity by the migration of free hydrated sodium ions in an environment of hydrated polar groups. In the part of the L₂-phase where the character of the phase is that of an aqueous solution the vapour pressure and conductivity are regulated by the concentration of molecularly dispersed acid sodium octanoate and its ions in water.     

SDBS/n-C8H18/n-C4OH/盐水体系中相微乳液双连续结构

微乳液是指由水（盐水）、油（烃）、一种或几种表面活性剂组成的热力学稳定体系,这类体系具有低粘度、各向导性、透明或半透明的性质[1],微乳液在许多工业实际问题中,例如润滑、以洗涤、催化等方面得到了应用[2],近年来,微乳液和反向胶束中酶催化技术的开发[3]以及分离蛋白质中的应用[4],使微乳液在生化技术研究中倍受青睐．与过剩盐水相和过剩油相达三相平衡时的微乳液即为中相微乳液。中相微乳液具有既可增溶水又可增溶油的特殊性质,并且微乳液与过剩水相和过剩油相间的界面张力（飞uw和7;n。;）极低顺干2．0。10－’1liN·111…     

Microemulstion synthesis of powders of water-soluble energy-saturated salts

The feasibility of preparing energy-saturated salts (NH₄NO₃, KNO₃, and NaBH₄) in powders with various particle sizes in microemulsion systems based on oxyethylated surfactant Tergitol NP-4 has been demonstrated. Powders were isolated by destroying microemulsions with acetone. The regions of micellar synthesis have been determined depending on the solubilization capacities and concentrations of the reagents and salts at a fixed Tergitol NP-4 concentration (0.25 mol/L). The morphologies and particle sizes of the thus-prepared salt powders were characterized by scanning electron microscopy (SEM), X-ray powder diffraction, differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravimetry; the hydrodynamic radii of microemulsions were characterized by photon-correlation spectroscopy.     

Formation of Microemulsions in Aqueous NaCl/Sodium (3-Dodecanoyloxy-2-Hydroxy-Propyl) Succinate/Glycerol Mono(2-Ethylhexyl) Ether/Oil Systems

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) forms microemulsions by mixing with cosurfactants such as glycerol mono(2-ethylhexyl) ether (MEH), although the combination with ordinary cosurfactant such as hexanol does not form a microemulsion of large solubilization. The middle-phase microemulsion coexists with excess water and oil (octane) phases at an optimum-mixing fraction of SLGMS and MEH in the presence of salt. The monomeric solubility of MEH in oil is low and MEH is mainly combined with SLGMS at an oil—water interface inside microemulsions. With decreasing salinity, the three-phase body shrinks and eventually disappears. The three-phase body may be terminated at a tricritical point, at which three phases simultaneously coexist. The effect of type of oil on the solubilization capacity of the microemulsions is also discussed.     

Thermodynamics of concentrated electrolyte mixtures. I. Activity coefficients in aqueous NaCl−NaCl2 at 25°C

The activity coefficients of NaCl and CaCl₂ in NaCl?CaCl₂ aqueous mixtures have been measured at 25°C in the ionic strength range I=0.1–20. Where NaCl solubility permitted, both activity coefficients were measured over the whole range of compositions from pure NaCl to pure CaCl₂ at constant I. The measurements were made using Na and Ca ion-selective electrodes vs. a Cl ion-selective electrode. The data are fitted to Harned equations of the form $$log \gamma _A = log \gamma _A^0 - \alpha _{AB} y_B - \beta _{AB} y_B^2$$ and were also analyzed using the Pitzer formalism. Excess free energies of mixing are calculated and presented in the I=0.1–5.0 range and the Friedman parameters calculated.     

Simultaneous TG,DTG and DTG analyses in controlled inert gas flow for the determination of deaquation steps of polyhydrated sulfates

The thermal deaquation reactions of CuSO₄·5H₂O and NiSO₄·7H₂0 were studied by simultaneous TG, DTG and DTA. In the CuSO₄·5H₂O thermogram three distinct steps corresponding to 2 moles,2moles. 1 mole of water were observed. and in the NiSO₄·7H₂O the sequence 1 mole, 3 moles, 2 moles, I mole was determined. The deaquation steps were correlated with the structure of water of crystallization. An exothermic DTA peak was observed during the evolution of the first mole of water in NiSO₄·7H₂O.     

Phase diagrams for the binary systems CaCl2-KCl and CaCl2-CaCrO4

Phase diagrams have been determined using differential thermal analysis for the binary systems CaCl₂-KCl and CaCl₂-CaCrO₄. CaCl₂-KCl phase diagrams have been previously reported but results were not consistent. No prior studies have been reported for the CaCl₂-CaCrO₄ system. In the CaCl₂-KCl binary system two eutectics have been located at 24.0 mole % KCl (m.p. 615°C) and 74.3 mole % KCl (m.p. 594°C). A double salt of composition CaKCl3 melting congruently at 741°C has been found. The CaCl₂-CaCrO₄ system is a simple eutectic system with the eutectic occurring at 23.4 mole % CaCrO₄ and melting at 660°C.     

The effect of counterions on the chain conformation of polyelectrolytes,as assessed by extensibility in elongational flow: The influence of multiple valency

An elongational flow technique was used to determine the effect of counterions on the chain conformation of polyelectrolyte molecules in solution, by means of the extensibility of the chains in the flow field. It is demonstrated that adding excess cations of seven low molecular weight salts, NaCl, CaCl₂, BaCl₂, SrCl₂, MgCl₂, AlCl₃, and SnCl₄, to a very dilute solution of fully sulphonated polystyrene (NaPSS) reduces the extensibility of the chains, that is, the facility by which a chain can be extended to varying degrees, an effect associated with chain contractions. In the case of multivalent counterions, these contractions, which with monovalent counterions are primarily due to screening of charges by excess counterions, are greatly enhanced, which we attribute to the formation of intramolecular ionic bridges. When, in the case of multivalent counterions, the polymer concentration is increased, in inversion of the effect, namely increase in chain extensibility on addition of ions, is observed. We attribute this latter effect to the ionic bridges becoming increasingly intermolecular, leading to effectively large molecules, and eventually to a gel. All these effects were accentuated with increase in valency. They could also be accompanied by precipitation which were of two kinds: one due to formation of insoluble ionic associations and a second attributable to enhanced hydrophobic interaction within the contracted chain itself. © 1994 John Wiley & Sons, Inc.     

烷基芳基磺酸盐结构对微乳液相行为的影响

用Winsor相图法研究了自制的6种不同结构的烷基芳基磺酸盐/不同醇/正癸烷/NaCl/水体系在不同温度下所形成的微乳液。 探讨了烷基芳基磺酸盐结构对微乳液相行为的影响。 同时考察了温度和醇对微乳液相行为的影响。 结果表明,随着烷基芳基磺酸盐长烷基链的增长,中相形成盐度S1、中相消失盐度S2、中相盐宽ΔS和最佳盐浓度S*值均减小,最佳中相体积V*M和最佳增容量σ*值均增大;随着烷基芳基磺酸盐分子的芳环向长烷基链中间位置移动,S1、S2、ΔS、S*值均减小,V*M和σ*值均增大;随着温度升高,V*M和σ*值均减小,S1、S2、ΔS、S*值均增大,在25 ℃时,体系无中相微乳液形成;随着正构醇碳原子数的增加,V*M和σ*值均增大,S1、S2、ΔS、S*值均减小。     

Oil-Induced Structural Change in Nonionic Microemulsions

Effect of added oil (heptane or squalane) on the microemulsion structures in polyoxyethylene dodecyl ether (C₁₂EO_n) systems was investigated by means of phase behavior and NMR diffusion experiments. In the binary water-C₁₂EO_n systems, an isotropic fluid, D₂ (or L₃), and an aqueous micellar solution, Wm, phases are successively formed with increasing the EO-chain length. Upon addition of heptane, D₂ and Wm phases are merged and a microemulsion of large solubilization is produced at a low surfactant concentration. With squalane, the solubilization of oil in D₂ phase is very low or almost zero, whereas the oil solubilization in Wm phase is relatively large. These structural changes in microemulsions are discussed based on the self-diffusion coefficients of water, oil, and surfactant measured by the PGSE-NMR method. The difference in the phase behavior may be attributed to the difference in the penetration tendency of oil in the surfactant palisade layer.     

Solubilization Enhancing Effect of A-B-Type Silicone Surfactants in Microemulsions

We report a solubilization enhancing effect of A-B-type silicone surfactants in microemulsions. The effect of added long-chain silicone surfactants, Si₂₅C₃EO_51.6 (extended length≈21.8 nm) and Si₁₄C₃EO_15.8 (extended length≈8.5 nm) on the solubilization capacity of C₁₂EO₅ (extended length≈3 nm)/water/dodecane microemulsion was investigated at the hydrophile-lipophile balance temperature at which a microemulsion (surfactant) phase containing equal weights of oil and water touches the three-phase body. The addition of silicone surfactants exhibits an enormous increase of the swelling of the middle phase primarily with an associated increase in the structural length scale of the microemulsion. The solubilization power increases with increasing x₂ (mole fraction of silicone surfactants to the total surfactant) and going through a maximum it decreases, since a lamellar liquid crystal introduces in the multiphase region at low surfactant concentrations. The solubilization capacity reaches at the maximum to an almost equal level for different x₂ values, 0.02 for Si₂₅C₃EO_51.6 and 0.09 for Si₁₄C₃EO_15.8. The solubilization power of the lamellar phase shows a similar trend with lower magnitude.