Standard Free Energy Of Micellization Research Articles

Preparation of dibasic acid‐containing soy phospholipids by chemical and enzyme‐catalyzed transesterification and evaluation of their surface‐active properties

AbstractThe preparation of dibasic acid‐containing soy phospholipid was made by transesterification reaction with alkyl ester of diabasic acid with both lipase and alkoxide as a catalyst. The extent of incorporation of a dibasic acid varied with the molecular size of the dibasic acid. The extent of incorporation in soy phospholipids was 4–13% in the case of adipic acid and 9–20% in the case of sebacic acid. The surface‐active properties of these modified soy phospholipids were examined and were found to be different from those of the original (unmodified) soy phospholipid. The interfacial properties such as critical micelle concentration (CMC), γCMC, surface excess concentration Γmax, and minimum area per molecule (Å), and thermodynamic parameters such as standard free energy of micellization, were found to depend on the hydrophobic part of the dibasic acids.

Micellization behaviour of sodium dodecyl sulfate in different electrolyte media

Critical micelle concentrations (cmc) of sodium dodecyl sulfate (SDS) in the presence of sodium chloride, sodium acetate, sodium propionate and sodium butyrate were measured by surface tension (at 20, 25 and 30 °C), conductance (at 25 °C) and EMF (at 25 °C) methods. Values of surface excess, counter ion binding constant, surface area, and standard free energies of micellization and adsorption of SDS in the presence of these electrolytes were also determined. The co-ions are found to have no effect on the cmc of SDS contrary to the report made earlier, but have an influence on its surface activity behaviour. Aggregation numbers were measured by using the steady-state fluorescence quenching method, whereas surface potentials were computed by solving the non-linearized Poission–Boltzmann equation. With added electrolyte aggregation number of SDS increases whereas its surface potential decreases. Butyrate co-ion affects the aggregation number of SDS when its concentration is ≥0.035 mol kg −1. This work has addressed the effect of co-ion on the adsorption and micellization parameters of SDS and the results have utility in designing formulations consisting of ionic surfactants and electrolytes for various applications.

Effect of aromatic ring in the alkyl chain on surface properties of arylalkyl surfactant solutions

AbstractSurface properties of two series of anionic arylalkyl surfactants, containing different aromatic rings in the straight aliphatic chain, sodium N‐aryloleyl‐N‐methyl‐2‐aminoethanesulfonates and sodium N‐aryloleyl p‐methoxyanili‐nesulfonates, were investigated. An increase of the aromatic ring size in the alkyl chain increases the critical micelle concentration (CMC) and surface tension at CMC. However, this also decreases the efficiency and effectiveness in reducing water surface tension. The dominant factor of the decrease of efficiency and effectiveness is attributed to the function of the hydrophilic segment and hydrophobic segment for arylalkyl surfactants, respectively. The same results are found in the standard free energy of adsorption (ΔGoads) and the standard free energy of micellization (ΔGomic) values. Moreover, with the increase of the aromatic ring size, the adsorption and micellization of arylalkyl surfactants begin to weaken. The data indicate that some parts of surface properties for arylalkyl surfactants are affected by the bulkiness of the arylalkyl chain. The results provide opportunities for further detailed examination of surface properties of arylalkyl surfactants with other branched alkyl chains.

The adsorption at solution–air interface and volumetric properties of mixtures of cationic and nonionic surfactants

Surface tension, density and conductivity measurements were carried out for systems containing mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol), Triton X-100 (TX100). The obtained results of the surface tension measurements were compared with those calculated from the relations derived by Joos, Miller and co-workers. From the comparison it appeared that using the modified adsorption isotherm derived by Joos the adsorption behaviour of CTAB and TX100 mixture can be predicted satisfactorily; however, the values of the surface tension of aqueous solutions of these mixtures calculated on the basis of the simple relationships of Miller et al. are a little higher than those measured in contrast to many two component systems of surfactants studied earlier. On the basis of the results obtained from the measurements and calculations it was found that there is a linear relationship between the surface tension and composition of CTAB and TX100 mixtures at their low concentration; however, in the concentration range corresponding to that of the saturated monolayer at the interface a negative deviation from the linear relationship is observed. This fact and the values of the parameters of molecular interactions in the mixed monolayer suggest that there is synergism in the reduction of the surface tension of aqueous solutions of CTAB and TX100 mixture when saturation of the monolayer is achieved. The negative parameters of intermolecular interaction in the mixed micelle and calculations based on MT theory of Blankschtein indicate that there is also synergism in the micelle formation for CTAB and TX100 mixture. It was also found that the values of the standard free energy of micellization for the mixture of CTAB and TX100 are somewhat lower than for individual components and they can be predicted on the basis of Maeda equation and the mole fraction of surfactant and free enthalpy of mixing CTAB and TX100 in the micelle. Our measurements and calculations indicate that the volume both of the individual surfactants and mixture studied decreases during the micellization process; however, at the concentration of the surfactants higher than CMC an increase of this volume is observed.

Conductometric studies of hexadecyltrimethylammonium bromide in aqueous solutions of ethanol and ethylene glycol

The effect of cosolvent on micellization of hexadecyltrimethyl ammonium bromide (CTAB) in aqueous solutions was studied. The conductivity of a mixture (cosolvent + water) as function of CTAB concentration was measured at different temperatures. Ethylene glycol and ethanol were used as a cosolvent. The conductivity data were used to determine the critical micelle concentration (CMC) and the effective degree of counterion dissociation of micelle in the temperature range 303.2 to 313.2 K. In all the cases studied, a linear relationship between log([CMC]mix/mol dm−3) and the mass fraction of cosolvent in solvent mixture has been observed. The free energy (ΔG mic 0 ), enthalpy (ΔH mic 0 ), and entropy (ΔS mic 0 ) of micellization were determined using the temperature dependence of CMC. The dependence of these thermodynamic parameters on solvent composition was determined. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the cosolvent content increases. The enthalpy and entropy of micellization are independent of temperature in pure water, while ΔH mic 0 and ΔS mic 0 decrease dramatically with temperature in mixed cosolvents. Furthermore, the entropic contribution is larger than the enthalpic one in pure water, while in the mixed solvents, the enthalpic contribution predominates.

Micellization Behaviour of Sodium Dodecylsulfate and Dioctyl Sulfosuccinate in the presence of Sodium Salicylate

Critical micelle concentrations of sodium dodecylsulfate (SDS) and dioctyl sulfosuccinate (AOT) were determined at 25 °C in aqueous medium as a function of sodium salicylate (NaSa) concentration by surface tension and EMF methods. In the case of SDS, conductance method was also used. Salicylate ion is found to affect the critical micelle concentrations of SDS and AOT when the concentration of NaSa becomes > 0.03 and 0.02 mol kg -1 , respectively. In the presence of NaSa, the counter ion binding constant for AOT has a single value equal to 0.47 and that for SDS is equal to 0.56. The higher value of the counter ion binding constant equal to about 0.8 observed earlier for AOT in sodium chloride, sodium acetate, sodium propionate and sodium butyrate solutions above 0.015 mol kg -1 of salt concentration has not been observed in NaSa solution. The effect of salicylate ion on the critical micelle concentration of SDS and AOT and on the counter ion binding constant of AOT is attributed to mixed micelle formation of salicylate with the anionic surfactants. It is considered that the salicylate ions reside just outside the Stern layer of the anionic micelles and form ion - pairs with the sodium ions bound to the micelles. Salicylate ion does not seem to have significant influence on the surface activity of SDS and AOT. Standard free energies of micellization and adsorption of SDS and AOT in the presence of NaSa were also evaluated.

Thermodynamics of aggregation of Tweens in the presence of diclofenac sodium

The effect of the addition of diclofenac sodium (DS) to the aqueous solution of non-ionic surfactants, polyoxyethylene sorbitan monolaurate, Tween-20 (T-20) and polyoxyethylene sorbitan monooleate, Tween-80 (T-80) has been investigated by means of conductivity and thermodynamic (density and speed of sound) studies at 25 °C. Studies have been carried out with variation in surfactant concentration at fixed [DS] = 5, 7, 9, 12 mM. The formulations have been characterized through the UV–vis spectroscopy. The spectra show a shift in λ max in the presence of Tweens. Critical micellization concentration, cmc, has been obtained from the conductivity–concentration plots. Conductivity results show an apparent change in curvature on addition of DS. Standard free energy of micellization, Δ G m ° , has been estimated based upon the mass–action model. Apparent molar properties, viz. V ϕ,s and K ϕ,s , have been computed from the density and ultrasonic velocity measurements. Limiting parameters of ϕ v ° and ϕ k ° have been used to explain the solvation of surfactant monomers in association with DS.

Alanine‐based surfactants: Synthesis and some surface properties

AbstractA homologous series of anionic surfactants, namely, sodium‐N‐(alkyloxycarbonyl) alanine (where alkyl=octyl‐, dodecyl‐, hexadecyl‐, and octadecyl‐) were synthesized having the formula: R‐OCO‐CH2NH‐CH2‐CH2‐COONa. Surface properties of their solutions, including surface tension, critical micelle concentration, effectiveness, maximum surface excess, and minimum surface area, were investigated for different concentrations at 25°C. The effects of these surfactants on the solubilization of a polar and a nonpolar solute were studied. Standard free energies of micellization and adsorption were calculated for the prepared surfactants in aqueous solution.

Surface and micellar properties of new nonionic gemini aldonamide-type surfactants

A new group of gemini aldonamide-type surfactants— N, N′-bisalkyl- N, N′-bis[(3-gluconylamide)propyl]ethylenediamines, N, N′-bisdodecyl- N, N′-bis[(3-glucoheptonylamide)propyl]ethylenediamine, and N, N′-bisalkyl- N, N′-bis[(3-lactobionylamide)propyl]ethylenediamines, (alkyl: n-C 8H 17, n-C 12H 25), were synthesized and characterized. The surface properties, such as surface excess concentration, Γ cmc, surface area demand per molecule, A min, efficiency in surface tension reduction, p C 20, the effectiveness of surface tension reduction, γ cmc, critical micelle concentration, cmc, and a measure of the tendency of the surfactant to adsorb at the aqueous/air interface relative to its tendency to form micelles in the bulk surfactant solution, cmc/ C 20, and standard free energy of micellization, Δ G mic 0, have been obtained by means of surface tension measurements. The standard fluorescence shift technique using PRODAN as a probe provide confirmation of the cmc values by an alternative method. Additionally, the micellar properties for the concentration near above the cmc have been characterized by the aggregation number, N agg. The presence of the dimeric segments with the aldonamide hydrophilic units in the surfactant molecule is found to be the source of their unusual physicochemical behavior. They are very efficient at adsorbing at the free surface and at forming micelles in water. Their critical micelle concentration values are remarkably low. They reveal remarkably low A min values in relation to conventional nonionic surfactants, which is unexpected from the molecular dimensions for the molecule but which is possible if one assumes some type of multilayer structure or a coherent interfacial film.

Thermodynamics and Micellar Properties of Tetradecyltrimethylammonium Bromide in Formamide–Water Mixtures

The effect of formamide on the micellization of tetradecyltrimethylammonium bromide has been investigated by conductance and fluorescence probe experiments. The critical micelle concentration and the degree of counterion dissociation of micelles were obtained from conductance measurements in the temperature range of 20 to 40°C. It was found that these two parameters increase with both temperature and formamide content in the solvent system. The thermodynamic parameters of micellization were estimated using the equilibrium model of micelle formation. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the formamide content in the mixed solvent increases, but it is roughly independent of temperature. Although the entropic contribution was found to be larger than the enthalpy one, in particular at lower temperatures, an enthalpy–entropy compensation effect was observed for all systems. Micellar aggregation numbers were determined by the static quenching method, using pyrene as a probe and cetylpyridinium chloride as a quencher. The observed decrease in the micelle aggregation number, which is controlled by the increase in the surface area per headgroup, was attributed to an enhanced solvation in formamide rich solvent mixtures. Changes in the pyrene 1:3 ratio index, indicating a more polar environment, are consistent with an increased micellar solvation. Fluorescence polarization of both coumarin 6 and fluorescein are indicative of a decrease in microviscosity with cosolvent addition. The data on fluorescence anisotropy of coumarin 6 were analyzed using the wobbling in cone model. Data indicated the formation of micelles with a less ordered structure as the formamide increases in the solvent system.

Surface Tensions, Critical Micelle Concentrations, and Standard Free Energies of Micellization of C8−Lecithin at Different pHs and Electrolyte Concentrations

The micellization of the amphiphilic zwitterionic dioctanoylphosphatidylcholine (diC8PC) in aqueous solution has been studied as a function of pH and electrolyte concentration. Critical micelle concentration (cmc) determined by surface tension measurements at pH 1.2, 3.2, 5.8, 7.4, and 10.0 indicated an increase with pH. To analyze the influence of electrolyte on the cmc, measurements of surface tension were performed at pH 1.2 and KCl concentrations in the range 0.1 M to 2.0 M. Here, the cmc decreased with increase of KCl concentration. Areas per molecule at the interface decrease from (86.8 to 65.1) Å2 molecule-1 with increase of pH. Standard Gibbs energies of micellization were calculated from the surface tension data and are in the range of approximately (−30 to −34) kJ mol-1. Data for the hydrocarbon volume of lipids, the effective area per headgroup, and the length of hydrocarbon chain have been used to estimate the shape factor of diC8PC micelles. The value for the shape factor indicates a gradual change from nonspherical (shape factor 0.49) to bilayers (shape factor 0.59).

Interfacial Solubilization of (5,10,15,20-Tetraphenylporphyrinato)zinc(II) in Cetyltrimethylammonium Chloride Reversed Micellar Solutions

Abstract The interaction between the zinc(II) complex of 5,10,15,20-tetraphenylporphyrin (Zn(tpp)) and cetyltrimethylammonium chloride (CTAC) at the interface of a CTAC reverse micelle in chloroform and 6 : 5 (v/v) chloroform–cyclohexane has been investigated spectrophotometrically. The spectra of Zn(tpp) in the CTAC reversed micellar solutions provide evidence of formation of the associated species Zn(tpp)CTAC; its Soret band is not influenced by solvent polarity. At a fixed molar ratio of water to surfactant (Rw = [H2O]/[CTAC]), the absorbance at the maximum of the Zn(tpp)CTAC band increases with an increase in the CTAC concentration. In the slope of the plot a discontinuity was found, due to formation of reverse micelles at this CTAC concentration, taken as the critical micelle concentration (cmc). The variations of the spectral data were interpreted quantitatively by applying the pseudophase model. Increasing Rw causes a decrease in the Zn(tpp)-solubilizing ability of reverse micelles, implying that the nucleophilicity of Cl- ion to the central zinc of the complex is dropped by the Cl- hydration at the interface. Furthermore, the standard free energy of micellization, calculated from the cmc data, indicates that the micellization is promoted by the Cl- hydration and by decreasing the chloroform fraction in the bulk organic phase.

Thermodynamic investigation of surfactant aggregation in 2-pyrrolidinone

The partial molal volume ( V φ,s) of several surfactants viz. sodium dodecylsulphate (SDS) and sodium tetradecylsulfate (STS), tetraethylammonium bromide (Tea-Br), Span-80, 60, 40, 20 in 2-pyrrolidinone have been determined at concentration below 0.80 mol kg −1 at 30 and 40 °C. The partial molal isentropic compressibility ( K φ,s) of micellar solutions of surfactants SDS, STS, Span-80, 60, 40, 20 have been calculated from ultrasonic velocity measurements at 30 °C. The infinite dilution values of V φ,s and K φ,s of the solubilizates in 2-pyrrolidinone are also estimated. The critical micellization concentration (cmc) values for the systems are taken at a concentration where a clear and well defined break is observed in the concentration dependence of the ultrasonic velocity. The cmc data has been utilized to compute standard free energy of micellization (Δ G m o). The results have been interpreted in terms of transfer of surfactant monomer from dispersed to aggregated state. Limiting parameters have been used to explain the solvation of surfactant molecules.

Micellar properties of long-chain alkyldimethylbenzylammonium chlorides in aqueous solutions

The temperature dependence of critical micelle concentration (cmc), micellar degree of ionization, β, and standard free energy of micellization, Δ G m o, of tetradecyl- and hexadecyldimethylbenzylammonium chlorides in aqueous solutions has been determined from conductivity data collected in the temperature range of 10–35 °C at 5 °C intervals. The occurrence of a second break on the specific conductivity against molality plots at about three times the cmc has been confirmed. From density measurements carried out at 15, 25 and 35 °C, the change of the apparent molar volume upon micellization of the surfactants was estimated. Density data for the tetradecyl homologue suggest the existence of an additional transition of the micelles at molalities about 15 times the cmc.

The Behavior of Sorbitan Surfactants at the Water–Oil Interface: Straight-Chained Hydrocarbons from Pentane to Dodecane as an Oil Phase

The interfacial tension of four sorbitan surfactants (Span 20, sorbitan monolaurate; Span 40, sorbitan monopalmitate; Span 60, sorbitan monostearate; and Span 80, sorbitan monooleate) was determined at the water–oil interface. Seven straight-chained hydrocarbons from pentane to dodecane were used as an oil phase. From the interfacial tension measurements the following values were calculated: critical micelle concentration (cmc), the interfacial tension at the cmc (γcmc), surface pressure at the cmc (πcmc), area per molecule at the cmc (Acmc), standard free energy of micellization (ΔG°mic), and standard free energy of adsorption (ΔG°ad). The shorter chained Span 20 and unsaturated Span 80 had higher cmc values and Span 80 had a larger molecular area than the other surfactants. With the same oil phase, differences between πcmc values of the four sorbitan monoesters were small, but the γcmc was slightly lowered as the hydrophobicity of the surfactant was increased. ΔG°mic was less negative for Span 20 and the ΔG°ad value was slightly more negative for Span 80. The effect of the oil phase was obvious. Increasing the hydrocarbon chain length of the oil phase increased γcmc and cmc values while πcmc and Acmc were decreased. As the length of the hydrocarbon chain of the oil phase was increased, ΔG°mic and ΔG°ad became less negative, which means a less spontaneous reaction.

Temperature Dependence of Equilibrium and Transport Properties of Decyldimethylbenzylammonium Chloride in Aqueous Solutions

Apparent and partial molar volumes of decyldimethylbenzylammonium chloride (C10DBACl) at (15, 25, and 35) °C have been calculated from results of density measurements. The specific conductivities of the solutions have been determined at the same temperatures. The results served for the estimation of critical micelle concentration, cmc, ionization degree, β, and standard free energy of micellization, , of the surfactant. From equivalent conductivity measured at 25 °C in the low concentration range, the transport number of the C10DBA+ cation has been estimated. The aggregation number, n, of the micelles has been estimated from the conductivity data.

Preparation and properties of new lactose‐based surfactants

AbstractA new group of nonionic saccharide‐based surfactants, N‐alkanoyl‐N‐methyllactitolamines (alkanoyl: decanoyl, lauroyl, myristoyl, palmitoyl, stearoyl), were synthesized and characterized. Surface properties such as critical micelle concentration, standard free energy of adsorption, standard free energy of micellization, surface tension reduction efficiency, effectiveness of surface tension reduction, surface excess concentration, and surface area demand per molecule as well as foaming properties (i.e., foam volume and foam stability), contact angle, antiraicrobial activity, and biodegradability were determined. The selected performance properties were evaluated in relation to commercially available alkyl polyglucosides (Glukopon 600 EC(HH)‐a Henkel product), and oligooxyethylenated decyl (C10E4) and dodecyl (E12E5) alcohols. The foaming‐stabilizing effect and contact angle suggest that the lactose‐derived surfactants that were studied share some common properties with alkyl polyglucosides that are different from those with an oligooxyethylene grouping. All tested N‐alkanoyl‐N‐methyllactitolamines were practically nontoxic to bacteria and yeasts. These compounds are readily biodegradable in the Closed Bottle test inoculated with activated sludge. N‐Alkanoyl‐N‐methyllactitolamines with lower chain lengths (C10–C14) biodegraded at a slightly faster rate. Biological properties showed that this class of compounds fulfills all requirements needed for environmental acceptance.

Conductivity, Density, and Adiabatic Compressibility of Dodecyldimethylbenzylammonium Chloride in Aqueous Solutions

Conductivities of dodecyldimethylbenzylammonium chloride in aqueous solutions were studied in the 15−35 °C temperature range at 5 °C intervals. Densities of the solutions were studied at 15, 20, and 25 °C. Adiabatic compressibility of the aqueous solutions of the surfactant has been determined from measurements of ultrasound velocity and density at 25 °C. The methods yielded identical critical micelle concentration (cmc) values. Conductivity results show a shallow minimum of the cmc values at around 25 °C. The ionization degree of micelles, β, increases, whereas the standard free energy of micellization, decreases upon growth of temperature. From density data for the surfactant, the change of the apparent molar volume upon micellization was calculated. The apparent adiabatic compressibility for the micelle of the surfactant at 25 °C was estimated. For comparative purposes we have measured additionally the conductivity of the decyl homologue at 30 °C to estimate the cmc and β values, and at 25 °C to estima...

Synthesis, Surface Properties, and Hydrolysis of Chemodegradable Anionic Surfactants: Diastereomeric Sodium Carboxylates Derived from 1,3-Dioxane

Mixtures of cis- and trans-2-n-alkyl-5-carboxy-5-methyl-1,3-dioxanes, 3a–3e, were obtained in the reaction of aliphatic aldehydes 1a–1e (from n-octanal to n-dodecanal) with 2,2-bis(hydro-xymethyl)propionic acid (DMPA), 2, carried out in boiling n-hexane or in the isomerization reaction of an appropriate cis-3a–3e. Pure trans-3a–3e were isolated from the above mixtures by selective crystallization and then converted into surface-active sodium salts, trans-4a–4e, by neutralization with sodium hydroxide or sodium methoxide. Surface properties of these surfactants, i.e., critical micelle concentration (CMC), surface excess concentration (ΓCMC), surface area demand per molecule (ACMC), effectiveness of surface tension reduction (γCMC), and standard free energy of micellization (ΔG°mic) were determined and compared with the appropriate surface properties of isomeric cis-4a–4e. It was shown that the properties of surfactants under study are dependent both on the length of a hydrophobic n-alkyl substituent at the C2 carbon atom of the 1,3-dioxane ring and on the configuration of a polar sodium carboxylate group at C5. The acids 3 undergo hydrolysis/isomerization reactions in acidic D2/d6-DMSO media. The cis isomers are hydrolyzed faster than trans isomers probably due to the steric hindrance of the axial methyl group at C5 of the latter ones.

Synthesis and surface properties of new dicephalic saccharide‐derived surfactants

AbstractA new group of nonionic dicephalic saccharide amides, N‐dodecyl‐N,N‐bis[(3‐d‐gluconylamido)propyl]‐amine, N‐dodecyl‐N,N‐bis[(3‐d‐glucoheptonylamido)propyl]‐amine, and N‐alkyl‐N,N‐bis[(3‐lactobionylamido)propyl]amines (alkyl: n‐C12H25′n‐C16H33′, n‐C18H37) were synthesized and characterized. Their structure and purity were confirmed by means of 1H and 13C nuclear magnetic resonance analysis and electrospray ionization mass spectrometry. Carbon spectra were verified using a DEPT experiment. The surface and interfacial properties such as critical micelle concentration (CMC), standard free energy of micellization, ΔGCMC, surface excess concentration, ΓCMC, and surface area demand per molecule, ACMC, were determined. The tertiary nitrogen atom seems to have a surprising effect on surfactnat packing at the interface.