Solutions of alkali soaps and water in fatty acids XI. Correlation between the acid sodium octanoate in the most water-rich part of the L2-phase and the acid soaps in two adjacent phases

The special nature of the outer-most water-rich region of theL ₂-phase in the ternary system sodium octanoate-octanoic acid-water is evidenced by its somewhat turbid appearance and by the character of its equilibria with adjacent phases. The phase contains aggregated acid sodium octanoate which is dispersed in a very dilute aqueous solution of sodium octanoate. The acid octanoate has the composition 1 NaC₈2 HC₈x H₂O and is composed of closely packed amphiphilic units, all with the polar groups in the same direction. This acid soap obviously forms double-layered aggregates with the lipophilic hydrocarbon chains pointing inwards and the polar groups pointing outwards towards the surrounding bulk-water. The phase is formed when octanoic acid is added to theL ₁-phase of the system just above the l.a.c.; in this aqueous solution, the acid reacts with dissolved acid octanoate 1 NaC₈1 HC₈x H₂O and that results in the formation of the slightly soluble acid soap 1 NaC₈ 2 HC₈x H₂O that separates as a new phase, the turbidL ₂ phase. On further addition of octanoic acid, the content of the mentioned acid soap increases until the solution phase is transformed into a liquid crystalline lamellarD-phase with the same acid soap composition. This formation of acid soap 1 NaA2 HA on addition of fatty acid to the dilute soap solution just above the l.a.c., has been known for a long time to occur in various systems containing a long-chain sodium soap. However, at suitably low temperatures, the reaction in these systems does not result in separation of the acid soap in the liquid crystalline, but in the solid crystalline state.     

Cyclopentadienyl, indenyl, and fluorenyl complexes of sodium with 15-crown-5

The sodium complexes [NaC₅H₅(15-crown-5)] (1a), [NaC₉H₇(15-crown-5)] (1b), and [NaC₁₃H₉(15-crown-5)] (1c, C₅H₅=cyclopentadienyl, C₉H₇=indenyl, C₁₃H₉=fluorenyl) were synthesized from NaC₅H₅, NaC₉H₇, NaC₁₃H₉, and 15-crown-5. Single crystal X-ray diffraction analyses were carried out for all three compounds 1a, 1b, 1c, and show that monomeric units were present in the solid state with the organic aromatic anion coordinated to the sodium cation via the five-membered ring.     

On the mechanism of the reduction of molecular nitrogen with aryldicyclopentadienyltitanium(III) complexes

The first step in the reduction of the dinitrogen ligand in (Cp₂TiR)₂N₂ (R  C₆H₅, m-, p-CH₃C₆H₄, C₆F₅, CH₂C₆H₅) by sodium napthalene (NaC₁₀H₈) involves the removal of one Cp group per titanium atom. The resulting diimide precursor reacts with a second mole of NaC₁₀H₈ with formation of a hydrazine precursor. This compound is thermally unstable and decomposes to an ammonia precursor. A minor part of the hydrazine precursor abstracts a proton from the solvent.     

Solutions of alkali soaps and water in fatty acids XIII. Circumstances that regulate the extension of theL 2-phase and the role of the acid-soaps rich in fatty acid for the occurrence of the phase

A basic requirement for that type ofL ₂-phase which exists in the system sodium octanoate-octanoic acid-water is the formation of acid-soaps. In order for the phase to be formed at all, the temperature must lie above the melting point of the fatty acid so that a reaction in non-aqueous milieu between neutral soap and fatty acid is possible. In order to obtain the characteristic shape and complete extension of the phase in direction of high water content the temperature must be so high that also the hydrated acid-soaps occur in fluid state. On the other hand the temperature cannot be so high that the acid-soaps become unstable.At temperatures at which the phase has obtained its full extension those circumstances differs which in different regions regulate the location of the phase borders; they depend on the composition of the acid soaps and on their amounts. In that part of the phase where the molar ratio between octanoic acid and sodium octanoate lies between 2 and 3 and where one has a continuous transition from reversed to normal structure only the two acid octanoates 1 NaC₈ 2 HC₈ x H₂O and 1 NaC₈ 3 HC₈ x H₂O occur and both are at 20 °C in fluid state.At water contents from about 22 % to 40 % the hydrate-water molecules belonging to the first mentioned soap are capable of contributing actively to the formation of large aggregates of acid-soap, a process which however is counteracted by the inmixing of the latter acid-soap. This mixture of the two acid-soaps decides in this region where the border of the phase will lie in direction towards an increased content of sodium octanoate; the result is that in spite of the fact that the hydration is increased, the border is only slowly displaced towards a higher content of fatty acid. As soon as the hydration of the acid octanoates has been completed and the additional water occurs as unbound bulkwater, the location of the phase boundary will no longer be influenced by the water content — now it will be the amphiphilic composition of the acid-soaps that determines the location of the border and it remains at the molar ratio 2.5 between octanoic acid and sodium octanoate at water contents from about 40% and up to 82%.In the direction of decreasing content of neutral sodium octanoate and increased content of water theL ₂-phase both at the highest content of fatty acid and the highest contents of water will be in equilibrium with the water-richL ₁-phase; in the first mentioned region with theL ₁-phase below the lac where at the border it is saturated with octanoic acid and in the latter region with theL ₁-phase just above the lac, where the dilute sodium octanoate solution contains dissolved 1 NaC₈ 1HC₈ x H₂O. In the large central part of theL ₂-phase, from about 20 % to about 86 % of water, the location of the border is dominated by the acid octanoate 1 NaC₈ 3 HC₈ x H₂O and that makes an equilibrium with theL ₁-phase impossible; instead one has an equilibrium via a two-phase zone between the amphiphile-rich region of theL ₂-phase and its water-rich region. In the first region the location of the border is regulated by the decreasing capability of the hydrated acid octanoate 1 NaC₈ 3 HC₈ x H₂O to dissolve octanoic acid; in the latter it is regulated by the fact that 1 NaC₈ 3 HC₈ x H₂O is the most fatty acid-rich acid-soap that is formed and that the octanoic acid is very little soluble in water and in the aqueous solution of this acidsoap.The middle part of theL ₂-phase, especially the region between about 55 % and 82 % of water, constitutes a direct continuation of the liquid crystalline lamellarD-phase. The liquid crystalline character of theD-phase is lost at the transition, but the lamellar organization is retained. That the molecules at least up to a water content of about 40 % are of the original reversed type and have an elongated shape with a central part of hydrated polar groups, from which core the hydrocarbon chains extend in two opposite directions, is the reason to that they, at crowding, form transient layer-like agglomerates of tightly packed more or less parallel molecules; this facilitates the transformation to coherent double amphiphilic layers, in which all molecules lie with the hydrated polar groups outwards toward coherent domains of bulk-water, without another liquid phase occurs.     

A molecular modeling study of pentanol solubilized in a sodium octanoate micelle

In order to study the structural and dynamical aspects of the solubilization process of pentanol within a sodium octanoate micelle a molecular dynamics simulation is presented. In this initial study we discuss the results and detailed insights into the interactions between sodium octanoate, pentanol, and water. The total micellar radius and the hydrophobic core radius were determined. The calculated values are in fairly good agreement with experimental results. In contrast to pure sodium octanoate micelles the aggregate with dissolved pentanol attained a more spherical shape related to the time interval of the simulation. It is clear that the results of a molecular dynamics computer simulation are always limited by its total length and the total time used for data analysis. Nevertheless, from our simulation study it turned out that a part of the pentanol hydroxyl groups were located within the micellar core and some alcohol molecules were also observed at the surface region of the micelle. The corresponding partition coefficient was calculated and agreed well with the experiment. The evaluated radial distribution functions of the sodium ions, the octanoate oxygens, and the hydroxyl hydrogens reveal details of the interface region of the micelle and the bulk phase. Additionally, it was possible to calculate the trans-to-gauche ratios of the alkyl chains and to compare these results with the simulation of a pure octanoate micelle.     

Thermodynamics of mixed micellar systems of sodium octanoate and ethoxylated alcohols in water at 25°C

Thermodynamic volume and compressibility properties of binary aqueous systems of sodium octanoate (C₈Na) and polyoxyethylene butyl ether compounds (ethoxylated alcohols), with one to three oxyethylene groups (C₄EO_X), and ternary systems of these compounds, have been determined as a function of surfactant and alcohol concentrations at 25°C from density and ultrasonic velocity measurements. Values of standard state apparent molar volume and apparent molar adiabatic compressibility properties of transfer of ethoxylated alcohols from water to aqueous C₈Na solutions were obtained. The observed trends in the properties of the aqueous binary C₈Na systems and of the transfer functions for C₄EO_x, at a given low concentration of 0.05m, were analyzed using theoretical models. Good agreement between the simulated results and the experimental data was achieved. The results obtained for the distribution coefficients of the alcohols and the thermodynamic properties of both components of the mixed micelle show that the hydrophobicity of the ethoxylated alcohols is enhanced by introducing more oxyethylene groups into the alcohol. The distribution behavior of these compounds between the C₈Na micelles and the aqueous phase also depends on the difference between the hydrophobicity of the surfactant and the alcohols.     

Solutions of alkali soaps and water in fatty acids VIII. Correlations of X-ray data with other experimental observations

In the system sodium octanoate-octanoic acid-water an obvious parallel exists between the low-angle X-ray observations in the isotropic liquidL ₂-phase and its composition, properties and structure. This parallel does not exist only with respect to the total content of acid sodium octanoates (with stoichiometric compositions 1NaC₈2HC₈x H₂O, and 1NaC₈3 HC₈x H₂O, where NaC₈=sodium octanoate and HC₈=octanoic acid) but also with respect to their amphiphilic composition and their water content (the value of x).In the region of 55–70% water, where the structure of the phase closely resembles, in many respects, that of the adjacent liquid crystalline lamellar D-phase, the dependence of of the quasi-Bragg values on concentration parallels that of the Bragg value in the mesophase, in spite of the disorder of aggregates in the isotropic phase. Furthermore, the numerical values of the quasi-Bragg spacings at given concentrations of the acid sodium octanoates are almost of the same sizes as those of the real Bragg spacings in the D-phase. In this region, the quasi-Bragg values give information of the same type about structure as do the real Bragg values in the D-phase; that is, information about the interplanar distances of adjacent double layers of acid soap, separated by intermediate layers of water.At low water contents (up to about 40%) where a direct comparison with a liquid crystalline phase is not possible, the quasi-Bragg values obviously increase in parallel with the molecular volume of the hydrated acid sodium actanoates and thus reflect one of the structural dimensions of these molecules. If one also considers those changes inside the molecules that, according to other observations, are caused by the incorporation of water, the mentioned parallel becomes still more obvious and it may be primarily the length of the hydrated acid soap molecules that is reflected in the quasi-Bragg values.At water contents above 40%, where increased amounts of unbound, bulk-water begin to appear in the phase, this parallel ceases. Above 55% water, where the phase obtains the character of an aqueous solution of hydrated acid sodium octanoates, the quasi-Bragg values are then shown to reflect the thickness of the aggregates of hydrated acid sodium octanoates (1 NaC₈2 HC₈x H₂O and 1NaC₈3 HC₈x H₂O) together with their intercalated layers of bulk-water.Based upon the comparison of X-ray phenomena with previously obtained experimental evidence, it is possible to draw some conclusions about the structure of theL ₂-phase. The most important is that the elongation of hydrated acid sodium actanoate molecules, caused by the incorporation of water up to about 40%, is strongly supported.     

Inclusions of methylene blue and phenothiazine by β-cyclodextrin in sodium dodecyl sulfate micelles

The inclusions of methylene blue and phenothiazine by β-cyclodextrin (β-CD) in sodium dodecyl sulfate (SDS) micelles and SDS/n-C₅H₁₁OH mixed micelles are studied by fluorescence spectroscopy. β-CD molecules can include monomers of methylene blue only after they have included SDS at a ratio of 1:1. However, phenothiazine can be included in the β-CD cavities even with β-CD concentrations lower than the total SDS concentration in SDS micelles, but not for solutions with SDS/n-C₅H₁₁OH mixed micelles.     

Phase equilibria and phase structure in the ternary systems sodium or potassium octanoate-octanoic acid-water

Two isotropic solution regions and several liquid crystalline regions occur in the ternary system sodium octanoate-octanoic acid-water at 20°C The solution regions are an aqueous solution and a solution of sodium octanoate and water in liquid octanoic acid. A region displaying one-dimensional lamellar structure is located in the center of the phase diagram. A region along the soap-water axis has a two-dimensional normal hexagonal structure. Another region at high octanoic acid content has a reversed hexagonal structure. Along the soap-fatty acid axis the acid-soap 2NaC₈:1HC₈ in crystalline state is found.X-ray and density findings for the various phases are presented, and structural parameters for the different liquid crystalline phases are estimated.The phase behavior of the potassium soap system is similar to that of the sodium system.The isothermal ternary phase diagram of a soap, the corresponding fatty acid and water provides information about the ionization state of the system, from the unionized fatty acid to the fully ionized soap.     

Surface and Solution Properties of Cationic Gemini Surfactants with Primary Linear Alkanols

Using surface tension and fluorescence methods, the surface and solution properties of two cationic gemini surfactants {pentanediyl-1,5-bis(dimethylcetylammonium bromide) and hexanediyl-1,6-bis(dimethylcetylammonium bromide)} (referred to as 16-5-16 and 16-6-16) have been studied in the presence and absence of primary linear alkanols. Parameters studied include the critical micelle concentration (CMC), C ₂₀ (the surfactant concentration required to reduce the surface tension of the solvent by 20 mN·m^?1), Г _max (maximum surface excess), and A _min (minimum surface area per molecule). These parameters indicate mixed micelle formation and, therefore, surfactant-additive interaction parameters in mixed micelles and mixed monolayers, as well as activity coefficients, were calculated. A synergistic effect was observed in all instances and was found to be correlated with the chain length of the alkanols. The CMC values of 16-s-16 (s = 5, 6) decrease with increasing alkanol concentration and the extent of this effect follows the sequence: 1-octanol (C₈OH) > 1-heptanol (C₇OH) > hexan-1-ol (C₆OH) > 1-pentanol (C₅OH) > butanol (C₄OH). The micelle aggregation number (N _agg) of mixed micelles has been obtained using the steady state fluorescence quenching method. The micropolarity of gemini/alkanol systems has been evaluated from the ratio of intensity of peaks (I ₁/I ₃) of the pyrene fluorescence emission spectra. Results are interpreted on the basis of the structure of mixed micelles and monolayers.     

Electrochemical polymerization of aniline in the SDS/n‐C5H11OH/H2SO4(aq) lyotropic liquid crystal

Electrochemical polymerization of aniline was performed by the method of ultramicroelectrode cyclic voltammetry in the lamellar liquid crystal and hexagonal liquid crystal of SDS/n‐C₅H₁₁OH/H₂SO₄(aq) system. The results indicate that the electrochemical polymerization of aniline can be catalyzed by the SDS/n‐C₅H₁₁OH/H₂SO₄(aq) lyotropic liquid crystal. The polymerization potential of aniline is smaller in the lyotropic liquid crystal system than that in the 0.10 mol L?1 sulfuric acid solution. The catalytic efficiency and polymerization rate of aniline increase with the n‐pentanol content, but decrease with the increase of the SDS content or [PhNH₂/H₂SO₄(aq)] content. Moreover, the catalytic efficiency of the lamellar liquid crystal exceeds that of the hexagonal liquid crystal in the SDS/n‐C₅H₁₁OH/H₂SO₄(aq) system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2388–2394, 2006     

FLUORESCENCE PROBE STUDIES ON THE SECOND CRITICAL MICELLE CONCENTRATION OF SEVERAL KINDS OF SURFACTANTS

The fluorescence intenstiy ratios (F₂/F₁) of excimer (F₂) to monomer (F₁) of probe (pyrene) were measured as a function of the concentration of the surfactant in several systems, which consist of sodium hexadecyl sulfonate (C₁₆As)-anionic surfactant, cetyltrimethylammonium bromide (CTAB)-cationic surfactant and pentaoxyethylene decyl ether (C₁₀E₅)-nonionic surfactant. The second CMC values were obtained according to F₂/F₁ ~ surfactant concentration curve break. In addition, we also studied the variation of second CMC vs NaCl concentration. It was found that the second CMC values of C₁₆A₅ and CTAB decreased with the increase of NaCl concentration. But the present of NaCl had no influence on the second CMC value of C₁₀E₅. Results showed that sphere-shaped micelles turn into rod-like micelle at the second CMC. The results were interpreted in terms of diffusion of pyrene molecules and the distribution of pyrene among micelles.     

Study on Binding Properties of Poorly Soluble Drug Trimethoprim in Anionic Micellar Solutions

Binding and distribution properties of trimethoprim (TMP) in the presence of various anionic surfactants; sodium octyl sulfate (C₈SO₄Na), sodium decyl sulfate (C₁₀SO₄Na), sodium lauryl sulfate (C₁₂SO₄Na), and sodium tetradecyl sulfate (C₁₄SO₄Na) has been studied by conductivity, spectrophotometry and surface tension measurements. The surface properties of anionic surfactants, that is, maximum surface excess concentration (Γ _max ) and minimum area per surfactant molecule (A _min ) at the air/water interface have been evaluated in the absence and presence of TMP using Gibbs adsorption isotherm. From conductivity data the ionization degree and counterion binding parameter have been obtained. Spectrophotometric experiments were used to determine binding constants of TMP to anionic micelles. With the increasing alkyl chain of surfactants, the interaction becomes stronger, which shows the importance of hydrophobic forces and incorporation of TMP molecules to the pure micelles of anionic surfactants increased. The results obtained from the surface tension and conductometric studies have been correlated with those obtained from the spectroscopic studies and binding tendency of TMP to anionic micelles followed the order as: C₁₄SO₄Na > C₁₂SO₄Na > C₁₀SO₄Na > C₈SO₄Na. From these results, the study of the interaction TMP in different anionic micellar solutions provided information about the characteristics of binding properties of poorly soluble drugs.     

The Inhibition of the Hydrolysis of Cephanone by CTAB/n‐C5H11OH/H2O Microemulsion

Abstract

The hydrolysis of cephanone in water, cetyl trimethyl ammonium bromide (CTAB) micelle, and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion was studied through UV‐VIS absorption spectroscopy. The mechanism of the hydrolysis and the effects of both the acidity of the media and the composition of O/W microemulsion on the hydrolysis were studied. The results show that the hydrolysis rate of cephanone increases with the acidity. Compared with water, CTAB micelle and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion suppress this hydrolysis. The inhibition of the hydrolysis of cephanone by CTAB micelle and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion is related to the location of cephanone in the interphases of CTAB micelles and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion droplets.     

Liquid–liquid equilibria of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate and sodium citrate/tartrate/acetate aqueous two-phase systems at 298.15 K: Experiment and correlation

Binodal curves of the aqueous 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄) + sodium citrate (Na₃C₆H₅O₇), [Bmim]BF₄ + sodium tartrate (Na₂C₄H₄O₆) and [Bmim]BF₄ + sodium acetate (NaC₂H₃O₂) systems have been determined experimentally at 298.15 K. The Merchuk equation was used to correlate the binodal data. The effective excluded volume (EEV) values obtained from the binodal model for these three systems were determined. The binodal curves and EEV both indicate that the salting-out abilities of the three salts follow the order: Na₃C₆H₅O₇ > Na₂C₄H₄O₆ > NaC₂H₃O₂. The liquid–liquid equilibrium (LLE) data were obtained by density determination and binodal curves correlation of these systems. Othmer–Tobias and Bancraft, and Setschenow equations were used for the correlation of the tie-line data. Good agreement was obtained with the experimental tie-line data with both models.     

Solutions of alkali soaps and water in fatty acids. XII. Correlations between the acid sodium octanoates in the isotropic liquidL 2-phase at water contents from 82% down to 10% and those in adjacent liquid crystalline phases

A close connection exists between the isotropic L₂-phase and the liquid crystalline lamellar D-phase. This connection is evidenced both with respect to similar compositions of their acid sodium octanoates and concerning the structure of the phases.The two-phase zone between these phases is very narrow, from 82 % down to about 55 % of water, it then widens slowly to about 40 % and thereafter very rapidly to 22 % of water; below the latter value it remains broad. The border of the L₂-phase is in the whole region from 82 % to 22 % of water located at molar ratios between octanoic acid and sodium octanoate of somewhat above 2.0; the border of the D-phase lies at the same values down to a water content of 40 %. The acid octanoate 1 NaC₈ 2 HC₈ x H₂O plays thus a considerable role in the phase transition all the way down to a water content of 22 %. As long as free bulk-water exists in both phases the structures in them remain alike; this similarity is greatest as long as the amount of bulk-water is so large that it suffices to form coherent domains. At contents of water below 40 %, that is after the disappearance of the bulk-water and when a decrease in the content of water begins to affect the hydration of the acid octanoates, the structural similarity between the phases disappears rapidly.     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

Light scattering and electrophoretic studies of mixed micelles of ionic and nonionic surfactants

Summary Light scattering and electrophoretic studies have been made of the mixed micelles formed in the systems ofn-dodecyl nonaoxyethylene ether/sodium dodecyl sulfate (NaC₁₂S), andi-octylphenyl nonaoxyethylene ether/NaC₁₂S as a function of the mole ratio of nonionic/ionic surfactants. In the former system the micellar molecular weight increases simply with increasing nonionic content, while in the latter system it rises abruptly when the nonionic content exceeds about 50% by mole. This behaviour would be interpreted by a difference in hydrocarbon-chain attraction between these two systems. The degree of ionic dissociation, , of NaC₁₂S in the mixed micelles increases as the content of the nonionic surfactant increases. This tendency is in accordance with the previous result obtained by pNa and vapor pressure depression data. The value of is closely related to the charge density, , on the surface of the micelle; increasing with decreasing . The micellar charge for NaC₁₂S alone, estimated from electrophoretic data, is much larger than that calculated from light scattering data by using the equation derived byMysels. For this discrepancy, a plausible explanation would be made by the different surfaces of the micelle measured by these two techniques.With 1 figure and 2 tables     

Effects of 2‐hydroxyalkyl methacrylates on the styrene miniemulsion polymerizations stabilized by SDS and alkyl methacrylates

The effects of 2‐hydroxyalkyl methacrylates (HEMA and HPMA) on the styrene miniemulsion polymerizations stabilized by SDS/lauryl methacrylate (LMA) or SDS/stearyl methacrylate (SMA) were investigated. A mixed mode of particle nucleation (monomer droplet nucleation and homogeneous nucleation) is operative during polymerization. Homogeneous nucleation plays a crucial role in the polymerizations stabilized by SDS/LMA, whereas monomer droplet nucleation becomes more important in the polymerizations stabilized by SDS/SMA. The polymerization kinetics is insensitive to the type of 2‐hydroxyalkyl methacrylates, but the difference in the relative importance of monomer droplet nucleation and homogeneous nucleation is detected. Incorporation of 1‐pentanol (C₅OH) into the reaction mixture also shows a significant influence on the polymerizations stabilized by SDS/LMA or SDS/SMA. This is attributed to the formation of a close‐packed structure of SDS and C₅OH on the droplet surface, which acts as a barrier to the incoming oligomeric radicals. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3188–3199, 2000