Properties of aqueous solutions for two binary mixed systems between two kinds of bile salts and nonionic surfactants

The micellar properties of aqueous binary mixed solutions for two systems consisting of sodium cholate (NaC)-octaoxyethylene glycol mono n-decyl ether (C₁₀E₈) and sodium glycocholate (NaGC)-C₁₀E₈ have been studied on the basis of surface tensions, polarity of the micelle interior and the mean aggregation number. Application of two theoretical treatments, based on regular solution and excess thermodynamic quantities for critical micellar concentration (CMC) data from surface tension curves of two mixed systems showed that the mole fraction of each bile salt in the mixed micelles near the CMC is lower than that of the corresponding prepared mole fraction in the mixed solution. The polarity of the interior suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of bile salt in the mixed solution and that the mixed micelles become dramatically more hydrophobic at a mole fraction of 0.68 for NaGC−C₁₀E₈ system and 0.75 for NaC−C₁₀E₈ system, respectively. This implies that the micelles become richer in the bile salt molecules and the tendency appears strongly for NaGC−C₁₀E₈ system due to the strong cohesion between the conjugated glycines in the NaGC molecules. The decrease of aggregation number with the increase of the mole fraction of bile salts shows that the micelles approach those of the single system of each bile salt. This supports the previously mentioned facts.     

Effects of sodium glycocholate and sodium taurocholate on the mixed micelles of bile salts and nonionic surfactant

Effects of sodium glycocholate (NaGC) and sodium taurocholate (NaTC) on the mixed micelles for two systems consisting of NaGC-octaoxyethylene glycol monon-decyl ether (C₁₀E₈) and NaTC-C₁₀E₈ have been studied as a function of the mixed micelles’ compositions, polarities of the micelles’ interior and mean aggregation numbers. The compositions of the mixed micelles are calculated from critical micelle concentration (CMC) data by using excess thermodynamic quantities. The polarities and mean aggregation numbers are determined from pyrene fluorescence in the mixed micelles. Both mixed systems were nonideal, and the mole fraction of NaGC or NaTC in a mixed micelle near the CMC was less than that in the aqueous mixed solution. However, the mixed micelle of the NaTC-C₁₀E₈ system contained more bile salt molecules than that of the NaGC-C₁₀E₈ system because of a good miscibility of NaTC and C₁₀E₈ molecules. The pyrene fluorescence results suggested that the mixed micelles changed from C₁₀E₈-rich micelles to NaGC- or NaTC-rich micelles, and mean aggregation numbers of the mixed micelles decreased abruptly with increasing mole fraction of bile salts. In the low mole fraction range of bile salts, however, both the polarities and the mean aggregation numbers for the NaTC-C₁₀E₈ system are lower than those for the NaGC-C₁₀E₈ system because of the high mole fraction of NaTC in a mixed micelle, and also because of the different effect of the conjugated group between NaTC and NaGC molecules in the mixed micelles.     

Mixed Micellization and Mixed Monolayer Formation of Sodium Cholate and Sodium Deoxycholate in Presence of Hydrophobic Salts Under Physiological Conditions

Mixed micellization and mixed monolayer formation of two bile salts namely sodium cholate (NaC) and sodium deoxycholate (NaDC), in the presence of sodium chloride (NaCl) and three hydrophobic salts including sodium acetate (NaAc), sodium butanoate (NaBu) and sodium hexanoate (NaHx) in 10 mM phosphate buffer (pH 6.5) at 37 °C were investigated by means of surface tension measurements. The experimental results were utilized to evaluate various parameters like critical micellar concentration (CMC), micellar and monolayer interaction parameter (β and β ^σ), micellar and monolayer mole fractions (X and Z), activity coefficients of two bile salts in mixed micelles and monolayer (f and f _(σ)), surface excess (Γ_max) and minimum surface area per molecule of bile salt (A _min). Mixed micelles and mixed monolayer were found to show slight non-ideality and both these phenomena have been found to be affected differently in the presence of various additive salts with NaHx showing larger effects. Higher efficiency of NaHx in affecting both phenomena has been attributed to its appreciable hydrophobicity and surface activity, thus showing stronger interactions with bile salt molecules.     

Micellar and Interfacial Behavior of Cationic Benzalkonium Chloride and Nonionic Polyoxyethylene Alkyl Ether Based Mixed Surfactant Systems

Micellar and interfacial properties of mixed surfactant systems comprising benzalkonium chloride, a cationic surfactant and nonionic polyoxyethylene alkyl ether surfactants (POE: C₁₀E₇, C₁₀E₈, C₁₀E₉, C₁₀E₁₀) have been investigated by surface tension, fluorescence and dynamic light scattering techniques. Critical micelle concentration (CMC) for different mixing mole fractions has been investigated by surface tension and fluorescence measurements. Ideal CMC, mixed micellar composition (X ₁ ^m , X ₁ ^σ ), interaction parameters for mixed micelles (β ^m) and adsorption monolayer (β ^σ ), surface excess concentration (Г_max), minimum area per molecule (A _min) and related thermodynamic properties have also been determined. Lowering of the CMC and negative interaction parameter values indicate synergism in the mixed micelle and monolayer formed, whereas, thermodynamic parameters evaluated for the proposed mixed systems indicate stability of the resulting micelles and monolayer. Micellar aggregation number (N _agg) and hydrodynamic diameter (D _h) computed from fluorescence and dynamic light scattering measurements respectively illustrate micellar growth in the mixed state. Results obtained for the proposed mixed systems can be helpful in designing smart materials for industrial surfactant based formulations.     

Solubilization of carotenoids from carrot juice and spinach in lipid phases: II. Modeling the duodenal environment

We have been investigating the factors determining the bioavailability of carotenoids from vegetables. The previous paper [Rich, G.T., Bailey, A.L., Faulks, R.M., Parker, M.L., Wickham, M.S.J., and Fillery-Travis, A. (2003) Solubilization of Carotenoids from Carrot Juice and Spinach in Lipid Phases: I. Modeling the Gastric Lumen, Lipids 38, 933–945] modeled the gastric lumen and studied the solubilization pathway of carotenes and lutein from carrot juice and homogenized spinach to oil. Using the same vegetable preparations, we have extended our investigations to solubilization pathways potentially available in the duodenum and looked at the ease of solubilization of carotenes and lutein within simplified lipid micellar and oil phases present within the duodenum during digestion. Micellar solubility of raw spinach carotenoids was low and was enhanced by freezing, which involved a blanching step. The efficiency of solubilization of carotenoids in glycodeoxycholate micelles decreased in the order lutein_carrot>lutein_{blanched-frozen spinach}>carotene_{blanched-frozen spinach}>carotene_carrot. Frozen spinach carotenoids were less soluble in simple micelles of taurocholate than of glycodeoxycholate. The results comparing the solubility of the carotenoids in mixed micelles (bile salt with lecithin) with simple bile salt micelles are explained by the relative stability of the carotenoid in the organelle compared to that in the micelle. The latter is largely determined by the polarity of the micelle. Below their critical micelle concentration (CMC), bile salts inhibit transfer of carotenoids from tissue to a lipid oil phase. Above their CMC, the bile salts that solubilize a carotenoid can provide an additional route to the oil from the tissue for that carotenoid by virtue of the equilibrium between micellar phases and the interfacial pathway. Mixed micellar phases inhibit transfer of both carotenoids from the tissue to the oil phase, thereby minimizing this futile pathway.     

Polycyclic hydrocarbon and polychlorinated biphenyl solubilization in aqueous solutions of mixed micelles

To determine the physiochemical behavior of xenobiotic hydrocarbons in simulated intestinal content, we examined the partition of 7,12-dimethylbenzanthracene (DMBA), 3-methyl cholanthrene (MC), benzo(a)pyrene, and a polychlorinated biphenyl compound (PCB, Aroclor 1242) between an emulsified oil phase and a mixed micellar solution. In a mixed lipid-bile salt system, negligible amounts of hydrocarbon were present in aqueous solution below the critical micellar concentration (CMC) of sodium taurocholate. Once the CMC was obtained, the 4 hydrocarbons exhibited nearly identical partitions from the lipid into the micellar system which was enhanced by increased concentrations of bile salt, reduction of triglyceride concentration and the formation of mixed rather than pure bile salt micelles. The partition of DMBA and MC into micelles was optimized by long-chain monounsaturated oleic acid and monooleoylglycerol as compared to their octanoic or linoleic counterparts. Linoleic acid and monolinoleoylglycerol maximized the partition of PCB from the oil into the micellar phase. In a mixed micellar system excluding an oil phase and an excess of DMBA, a molar saturation ratio (mol hydrocarbon:mol bile salt) was calculated by regression analysis to be 0.162. This indicates that more than one molecule of hydrocarbon is solubilized per mixed micelle and that the aqueous solubilization of hydrocarbon may be attributed to true micellar solubilization.     

α-Sulfonato palmitic acid methyl ester-hexaoxyethylene monododecyl ether mixed surfactant system: Interfacial,thermodynamic, and performance property study

Interfacial, thermodynamic, and performance properties of aqueous binary mixtures of α-sulfonato palmitic acid methyl ester, C₁₄H₂₉CH(SO₃Na)COOCH₃(PES), and hexaoxyethylene monododecyl ether, CH₃(CH₂)₁₁(OCH₂CH₂)₆OH (C₁₂E₆), were investigated with tensiometric, conductometric, fluorimetric, and viscometric techniques. The critical micelle concentration (CMC), maximum surface excess, minimum area per molecule of surfactant at the air/water interface, and the thermodynamics of micellization and adsorption were determined. The CMC was very low for mixed systems, indicating probable use as a detergent with less effect on the environment because of surfactant biodegradability and less amount in the environment. The interaction parameter β^m, computed by using the theory of Rubingh and Maeda, indicated an attractive interaction (synergism) between the surfactant molecules, which was also confirmed by proton nuclear magnetic resonance studies in the mixed micelle. The micellar aggregation number (N _agg), determined by using a steady-state fluorescence quenching method at a total surfactant concentration of about ∼10 mM at 25°C, was almost independent of the surfactant mixture composition. The micropolarity and the binding constant (K _sv) for the C₁₂E₆/PES mixed system were determined by the ratio of the intensities (I ₁/I ₃) of the pyrene fluorescence emission spectrum, and the local microenvironment inside the micelle was found to be polar. The viscosity of the mixed system at all mole fractions suggested that mixed micelles are nonspherical in nature. The cloud point of oxyethylene group-containing surfactants was increased by the addition of PES. Foaming was temperature dependent, and a 1∶1 mixed system showed minimum foaming. All performance properties were composition dependent.     

An octaethylene glycol monododecyl ether-based mixed micellar assay for determining the lipid acyl hydrolase activity of patatin

Patatin was extracted from potato tubers (Solanum tuberosum L. cv. Spunta) and purified to homogeneity by ammonium sulfate salt fractionation and one sole chromatographic step. A spectrophotometric mixed micellar assay for patatin lipid acyl hydrolase (LAH) activity was designed with the detergent octaethylene glycol monododecyl ether (C₁₂E₈). Patatin LAH used p-nitrophenyl butyrate (PNP-butyrate) as substrate when solubilized in (C₁₂E₈) micelles. In the mixed micellar system, patatin LAH responds to the PNP-butyrate surface concentration expressed as mol% (=[PNP-butyrate]·100/([detergent]-critical micellar concentration)) and not to the molarity of PNP-butyrate. The kinetic parameters were determinined; V _max was independent of the mixed micelle concentration, as was K _m, when expressed as mol%. However, K _m was dependent on C₁₂E₈ concentration when expressed in molar concentration. C₁₂E₈/PNP-butyrate proved to be a reliable system for assaying patatin LAH activity and is superior to the commonly used Triton X-100 and SDS methods. It permits investigation of the substrate requirements of patatin LAH activity because the concentration-independent K _m can be determined both in mol% and as the absolute number of substrate molecules per micelle. In addition, the detergent did not affect the enzyme activity.     

Synthesis and surface-active properties of trimeric-type anionic surfactants derived from tris(2-aminoethyl)amine

Trimeric-type anionic surfactants (3C_ntaAm, where n is a hydrocarbon chain length of 8, 10, or 12) with three hydrocarbon chains and three carboxylate headgroups were synthesized from tris(2-aminoethyl)amine, and their properties were investigated by surface tension, electrical conductivity, dynamic and static light-scattering, fluorescence of pyrene, and emulsification power techniques. The critical micelle concentrations (CMC) of 3C_ntaAm were 0.00092–0.00834 mmol dm⁻³, and the surface tensions at the CMC were 33.3–39.9 mN m⁻¹. The areas per molecule occupied by 3C₁₀taAm and 3C₁₂taAm were extremely small, showing they were highly compact at the air/water interface. In addition, adsorption or micellization behavior of 3C_ntaAm was estimated by parameters such as pC ₂₀ (the efficiency of surface adsorption), CMC/C ₂₀ (the ease of adsorption relative to the ease of micellization), and ΔG _M ^o (Gibbs energy of micellization). Dynamic and static light-scattering mesurements of 3C_ntaAm showed a hydrodynamic radius of 45–61 nm above the CMC and aggregation numbers of 10–82 at the CMC, respectively. The fluorescence intensity ratio of the first to the third band in the emission spectra of pyrene started to lower from far above the CMC for 3C₈taAm and 3C₁₀taAm, and below the CMC for 3C₁₂taAm. This suggests that loose micelles or premicellar aggregates are formed in solutions. Mixtures of aqueous solutions of 3C_ntaAm and toluene formed oil-in-water-type emulsions, and the stabilizing abilities were in the order of 3C₈taAm>3C₁₀taAm>3C₁₂taAm. The degree of emulsification of 3C₈taAm remained at 69% after 24 h of standing. Thus, 3C_ntaAm exhibited unique properties superior to monomeric or dimeric surfactants that were significantly influenced by their hydrocarbon chain lengths.     

Characteristics of solubilization and encapsulation of fullerene C60 in non-ionic Triton X-100 micelles

The solubilization and encapsulation of monomeric C₆₀ in Triton X-100 micelles were investigated. Characteristic hydrophobic interactions of the type π-π and CH-π between the Triton X-100 micelle and C₆₀ resulted in stable aqueous dispersions of C₆₀ in the micellar medium, as evidenced from UV-vis, fluorescence emission and micro-Raman spectroscopy. Cyclic voltammetry of C₆₀ encapsulated Triton X-100 in aqueous 5 mM LiClO₄ solution revealed a quasi-reversible one-electron reduction peak with E_1/2 = −0.61 V and a reversible reduction peak at E_1/2 = −1.11 V vs. Ag/AgCl reference electrode at a scan rate of 10 mV s⁻¹, a redox behaviour drifting substantially from that of pure C₆₀. An onset concentration of ∼0.025 mM for C₆₀ aggregation in the micellar core was substantiated from the characteristic absorption spectral broadening and quenching of pyrene fluorescence. The molar solubilization capacity of C₆₀ in aqueous Triton X-100 micellar solution was estimated spectrophotometrically to be 0.22.     

The incorporation of fatty acids of different chain length into liver and biliary lipids in the perfused rat liver

In an attempt to correlate the incorporation of fatty acids (FA) of different chain length into liver and biliary lipids’ isolated rat livers were perfused for 2 h with Krebs-Ringer bicarbonate containing 1% albumin and 10 μmol of [1-¹⁴C]-labeled FA: C₂’ C₈’ C₁₀’ C₁₂’ C₁₆’ and C_18∶1. One to 1.36 μmol of medium-chain fatty acids (MCFA’ C₈’ C₁₀’ and C₁₂) and 6.6 μmol of long-chain FA (LCFA) were incorporated into liver lipids’ 40% of the latter into phosphatidylcholine (PC). ¹⁴C-acetate (13 nmol) was incorporated into biliary cholesterol; ¹⁴C-MCFA contributed only 3.2–5 nmol; LCFA did not lead to newly synthesized cholesterol. Newly synthesized liver PC (2.75 to 3.25%) and newly synthesized liver cholesterol (6.5 to 10%) were secreted into bile. The specific radioactivity of biliary PC after infusion of all-saturated FA was 3.8–6.8 times higher than that of liver PC; for C_18∶1 it was only 1.7-fold. The specific radioactivity of biliary cholesterol’ as compared to liver cholesterol’ was 12 times higher for C₂ and five times higher for MCFA. This indicates that a considerable proportion of the newly synthesized lipids was secreted into bile prior to significant mixing with preexisting liver PC and cholesterol pools. liver PC contained 8% of unchanged ¹⁴C−C₁₂; while ¹⁴C−C₁₀ was not detected. Biliary PC’ in contrast’ contained 18% of unchanged ¹⁴C−C₁₂ and 3% ¹⁴C−C₁₀. These results suggest that after prolonged infusion of medium-chain triacylglycerols/longchain triacylglycerols to patients’ biliary PC may become enriched with MCFA. In addition’ the oxidation of these FA may provide C-2 units which increase cholesterol synthesis.     

Determination of pK a Values of Oxocholanoic Acids by Potentiometric Titration

The pK _a and the maximum solubility values of cholic, deoxycholic salts and their oxo-derivatives have been measured by the method of potentiometric titration. In the monomer phase (under the critical micellar concentration, CMC), the bile salts have different pK _a values, as a result of their structural differences (the number of hydroxyl and oxo groups in the steroid skeleton) and different hydration properties of the acid anions. In the micellar phase (above the CMC), the bile salts have higher pK _a values than in the monomer phase (under the CMC). This increase in the pK _a values is greater in more hydrophobic bile salts (cholate and deoxycholate), than in less hydrophobic oxo derivatives, which can be explained by the different aggregation numbers of these bile salts. The oxo-derivatives are more likely to form dimeric micelles, where the carboxylic groups are situated on the two sides of the micelle, not causing any electrostatic repulsion. In the more hydrophobic bile salts, aggregation numbers are higher, which causes electrostatic repulsion of the nearby situated carboxylic anions and consequential protonation of these anions (which leads to the stabilization of the micelle). The maximum solubility values are higher for the oxo-derivatives. If the steroid skeleton of the bile salt is more hydrophobic, the capacity to solubilize the unionized bile acid is higher, i.e. a smaller amount of the bile acid anion is needed for the solubilization of the bile acid monomer. The oxo-derivatives are less hydrophobic, but alongside their hydrophobicity, the structure of the micelle determines the solubilization capacities.     

Conductometric Probe Analysis of the Effect of Benzyldimethylhexadecylammonium Chloride on the Micellization Behavior of Dodecyltrimethylammonium Bromide in Aqueous/Urea Solution: Investigation of Concentration and Temperature Effect

Surfactant mixtures are used in many different industrial formulations. In this study, the mixed micelle formation behavior of 2 different cationic surfactants, namely dodecyltrimethylammonium bromide (DTAB) and benzyldimethylhexadecylammonium chloride (BDHAC), in the absence and presence of urea at various temperatures (298.15–318.15 K) was studied using the conductometric method. The attractive interaction between DTAB and BDHAC was estimated from the values of critical micelle concentration (CMC) and the CMC for ideal mixing (CMC^id). Urea increases the CMC value as a result of the enrichment in the surface charge of the micelles/mixed micelles. The values of micellar mole fraction (X₁^Rub [Rubingh], X₁^M [Motomura], X₁^Rod [Rodenas]) and ideal micellar (X₁^id) of surfactant BDHAC were obtained by different models and are shown to exhibit the high contribution or effective involvement of BDHAC in mixed micelles and increase with increasing BDHAC mole fraction (α₁). Activity coefficients (f₁ and f₂) were also evaluated from the relevant formula given in the literature. The negative values of the interaction parameters (β) show the attractive interaction among the studied components. Excess Gibbs free energy (?G_ex) of micellization revealed that the stability of mixed micelles is higher in aqueous solution than in urea solution. The thermodynamic parameters, namely the Gibbs free energy change, enthalpy change, and entropy change (?G^o_m, ΔH^o_m, and ?S^o_m, respectively), were also calculated from the conventional standard equations.     

Mixed micelles of cationic surfactants and bile acid salts in aqueous media

Critical micelle concentrations of cetyltrimethylammonium-p-toluene sulfonate (CTAT) and cetylpyridinium chloride (CPC) with sodium cholate (NaC) and sodium deoxycholate (NaDC) were determined in aqueous solutions by surface tension measurements. Interaction parameters and mole fraction of the components in mixed micelles were estimated using Rubingh's theory. Strong interaction was observed for each mixed system, a common feature shown by anionic-cationic mixtures. Dramatic effects on the viscosities of these cationic surfactant-bile salt mixtures were seen, and were markedly dependent upon the counterion of the cationic surfactant and the nature of bile salts. Micelles are small and spherical for cationic surfactants in the presence of NaC. Micelle growth was seen for CPC in the presence of NaDC by an increase in viscosity, but a CTAT solution showed an opposite effect on addition of NaDC. Conductance results supported this view. Different behavior of the two bile salts is explained on the basis of their orientation in cationic micelles.     

Mixed monolayer and mixed micelle formation in binary mixture of surfactants—Systems for trioxyethylenated dodecyl sulfonate and some polyoxyethylenated fatty alcohol ether nonionic surfactants

The interaction and synergism of some polyoxyethylenated fatty alcohol ether (POE) nonionic surfactants (C₁₂E₂, C₁₂E₃, C₁₀E₅, C₁₀E₇, where C_x indicates number of carbon atoms in the chain and E_y indicates number of oxyethylene glycol ethers) with trioxyethylenated dodecyl sulfonate (C₁₂E₃S) in mixed monolayer formation at the surface and in mixed micelle formation in aqueous solutions were studied at 25 and 40°C by calculating interaction parameters (β_α, β_M) from surface tension-concentration data by use of Rosen's equations based on the nonideal solution theory. All the systems investigated adapt reasonably well to the nonideal model, with negative values of β_σ and β_M (where M means micelle and σ refers to the air-liquid interface) indicating a favorable interaction between the mixed surfactants. Either at a monolayer or in a mixed micelle, the attractive interaction becomes stronger when the alkyl chain in the POE surfactant is longer, i.e., when the POE becomes more hydrophobic. The interaction increases in the order C₁₀E₇<C₁₀E₅<C₁₂E₃, C₁₂E₂. For the two C₁₀E _n (n= 5,7)/C₁₂E₃S systems, as temperature increases from 25 to 40°C, the interaction increases in a mixed micelle, but it decreases in a mixed monolayer. Synergism in mixed micelle formation exists for C₁₂E₃S/C₁₀E _n mixtures when X₁ ^M , the mole fraction of POE in a mixed micelle, is ≈0.4–0.8, whereas synergism does not occur in the systems of C₁₂E₃S/C₁₂E _m due to the large difference between CMC₁ and CMC₂, i.e., large |In(C ₁ ^M /C ₂ ^M )| value (where CMC=critical micelle concentration). The degree of synergism in mixed micelle formation is temperature independent and is 0.23, 0.18, and close to zero for C₁₀E₅/C₁₂E₃S, C₁₀E₇/C₁₂E₃S, and C₁₂E _m (m=2,3)/C₁₂E₃S systems, respectively. Synergism in surface tension reduction effectiveness occurs in C₁₂E₃S/C₁₂E₂ and C₁₂E₃S/C₁₂E₃ systems. The mole fractions of POE in the solution phase are 0.302 and 0.333 for the two mixtures at the point of maximum synergism.     

Interactions Between an Anionic Fluorosurfactant and a PEO-PPO-PEO Triblock Copolymer in Aqueous Solutions

Surface tensions were determined for a mixture of an anionic fluorinated surfactant and a PEO-PPO-PEO triblock copolymer. The interactions between the two surfactant molecules in the mixed monolayer and the mixed micelle were studied through molecular interaction parameters (β ^σ, β ^M) and the molecule exchange energy (ε, ε _m). It was noted that synergism and strong attractive interactions took place between the anionic fluorinated surfactant and the triblock copolymer molecules in both mixed micelles and mixed monolayers, reflected by the interaction parameter values of between −10 and −18 for all mixtures investigated. Moreover, it can be seen from the value of (ε − ε _m) that when the mixture has a small amount of triblock copolymer, the formation of mixed micelle results in a greater decrease in energy than does the formation of a mixed monolayer. With an increase in the mole fraction of the triblock copolymer in the mixture, in order to obtain the lowest surface energy, surfactants tend to form mixed monolayers first, and then form mixed micelles.     

Effect of solubilized amines on the structural transition of cetyltrimethylammonium bromide micelles in aqueous potassium bromide

Rod-shaped micelles were produced by mixing 0.1 M cetyltrimethylammonium bromide (CTAB) and 0.1 M KBr in aqueous solution. The effects of the addition of aliphaticn-amines (C₄, C₆, C₇ and C₈) and temperature on the shape of micelles were studied by viscosity measurements. The viscosity data show that transition of rod-shaped micelles to larger aggregates is induced by addition of higher amines (≥C₆) up to a certain concentration; a further increase in concentration produced the opposite effect. Addition of C₄-amine induces only a rod-to-sphere transition. The data were interpreted in terms of solubilization/incorporation (decrease of micellar surface charge density) of amines inside the micelles and the nature of the effective solvent (water+amine). The latter effect dominated the change from larger aggregates to smaller micelles at higher concentrations of the added amine. Increasing the temperature produced effects similar to C₄-amine addition, namely, rod-to-sphere transition. Activation free energy (ΔG^*) and enthalpy (ΔH^*) were also computed from the temperature dependence of the viscosity. ΔG^* and ΔH^* values were higher for larger aggregates (long rods) than for smaller ones (spherical micelles) and ΔH^* covered almost the total contribution to ΔG^*.     

Synthesis and properties of N-(α-carboxyalkyl)acrylamide telomer-type surfactants having multihydrocarbon chains

N-(α-Carboxyalkyl)acrylamide telomer-type surfactants (xC _n−1 AmAc where n is alkyl chain length=6, 8, 10, 12; and x is degree of polymerization=3.3–13.1) were synthesized by the telomerization of monomer (C _n−1 AmAc) in the presence of the corresponding alkanethiol as a chain transfer agent and then investigated for their surface-active properties. xC _n−1 AmAc telomers lowered the surface tension of aqueous solutions that were at pH 9–10. The critical micelle concentrations (CMC) of the telomers were lower than those of the monomers with the same alkyl chain length, and the CMC values shifted to lower concentrations with both increasing alkyl chain length and polymerization degree. xC₉AmAc with x=3.3–6.3 gave the highest efficiencies in lowering the surface tension. The cross-sectional molecular areas per molecule of xC _n−1 AmAc telomers were smaller than the values estimated on the assumption that they are assemblies of C _n−1 AmAc monomer units. The foaming abilities and the foam stabilities were both in the orders of xC₇AmAc>xC₉AmAc>xC₅AmAc>xC₁₁AmAc. Mixtures of aqueous solutions of xC _n−1 AmAc telomers and toluene formed oil-in-water emulsions. The emulsion-stabilizing abilities were in the orders of xC₇AmAc>xC₅AmAc>xC₉AmAc=xC₁₁AmAc. The addition of Ca²⁺ to the mixed solutions of telomers and toluene resulted in formation of water-in-oil type emulsions. Thus, the surface-active properties of the telomers were influenced significantly by the alkyl chain length and the polymerization degree of the telomers. In addition, these properties could be correlated with the hydrophilic-lipophilic balance (HLB); the highest surface activities were observed by using xC _n−1 AmAc with HLB of 14–18.     

Mixed micelles of hexadecylpyridinium bromide + tetradecyltrimethylammonium bromide in aqueous glycol oligomers

Conductances of hexadecylpyridinium bromide (HPyBr) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyBr (α_HPyBr) were measured in pure water as well as in the presence of various aqueous ethylene glycol oligomers containing 10 and 30 wt% of each additive in their respective binary mixtures at 30°C. Each conductivity curve shows two breaks corresponding to two critical micelle concentrations (cmc; C₁ and C₂ over the whole mole fraction range of HPyBr + TTAB mixtures except in the presence of pure HPyBr and TTAB, where a single break was observed. From the conductivity data, various micellar paramelers in the absence and presence of glycol additives were computed. A variation in the micellar parameters in the presence of additive showed that additive introduction mainly influence the medium properties and therefore the micellar properties. However, no significant micelle-glycol interactions were observed even with an increase in the number of repeating units from ethylene glycol to polyethylene glycol 600. The mixing behavior of HPyBr + TTAB is close to nonideal and is identical in pure water and in the presence of various glycols. This has been attributed to the presence of synergistic interactions between unlike monomers at C₁ that are not influenced even by the presence of additives. The appearance of the second cmc is mainly attributed to structural transitions of the mixed micelles at C₁ with a further increase in surfactant concentration.