The aggregation of aqueous dodecylphosphonic acid in dodecyltrimethylammonium hydroxide mixtures

The aggregation of aqueous dodecylphosphonic acid (DPA) and dodecyltrimethylammonium hydroxide (DTAOH) mixtures was studied by several methods. The behavior of DPA-rich mixtures is close to that of pure DPA. This is probably due to the preservation of the hydrogen-bonded structure of the micellar headgroup layer. The behavior is almost ideal. Betweeny _DPA =0.5 and 0.33 (y _DPA being the mole fraction of DPA in the surfactant mixture), the hydrogen-bonded structure of the micellar headgroup layer is destroyed. A sort of micellar azeotrope is formed, and the maximum of non-ideal interaction between the two surfactants is attained aty _DPA =0.4. Fory _DPA <0.33 the system behaves as a common mixture of a cationic surfactant and a non-ionic one (DPA.2LTA). There is a phenomenon of counterion condensation on aggregates at concentrations over the CMC.     

The aggregation of sodium dehydrocholate in water

 We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10⁻⁴ mol dm⁻³ there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10⁻⁴ and (5.2 ± 2.2) × 10⁻³ mol dm⁻³, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10⁻² mol dm⁻³ the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10⁻² mol dm⁻³, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts. Received: 14 May 2001 Accepted: 10 August 2001     

The aggregation in dodecyltrimethylammonium hydroxide aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC _T=(2.51±0.10)×10^–4 mol · dm^–3 the surface excess becomes zero, atC _T=(1.300±0.041)×10^–3 mol · dm^–3 small aggregates from, which grow with concentration. AtC _T=(1.108±0.010)×10^–2 mol · dm^–3 true micelles form (CMC) and at (3.02±0.28)×10^–2 mol · dm^–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases.     

Low-concentration aqueous solutions of undecenoic acid and sodium undecenoate

The behaviors of low-concentration aqueous solutions of 10-undecenoic acid and its sodium salt were studied by several techniques. The acid does not have a critical micelle concentration, but gives an emulsion of very small droplets at (0.8–1) ×  10⁻⁴ mol dm⁻³. The emulsion was clearly visible by eye at 0.002 mol dm⁻³. The sodium salt has a stepwise aggregation process, giving premicellar aggregates at 0.023 ± 0.008 mol dm⁻³, which grow to form micelles at 0.117 ± 0.007 mol dm⁻³. The compositions of the solution and the micelles were also studied. Received: 25 February 1999 Accepted in revised form: 21 June 1999     

Efficiency of sildenafil encapsulation in poloxamer micelles

Abstract

The purpose of this study is to prepare and investigate the physicochemical and thermodynamic evidence of sildenafil (SIL) encapsulated poloxamer 188 (P188) micelles. The micelles were prepared by the thin-film hydration technique and investigated by pendant drop tensiometry and dynamic light scattering techniques. The closed association model was used to determine the micelle-monomer equilibrium parameters. The standard Gibbs free energy of the micelle formation was calculated from the partition coefficient. The change in the pattern of the surface tension, particle count rate, and particle size of the SIL encapsulated P188 micelles was observed. The corresponding critical micelle concentration (CMC) was approximately 0.04?mM. The hydrodynamic Z-average size of the micelles ranged from 6 to 9 d. nm. The encapsulation efficiency (EE) of SIL in the micelles was up to 54.3?±?0.2%. The obtained equilibrium constant was 0.67. The standard Gibbs free energy of the formation of SIL encapsulated micelles at 25?°C was ?32.9?kJ/mol. The formation of SIL encapsulated P188 micelles was confirmed by the change in the pattern of the surface tension, particle count rate and size of the micellar solution. The standard Gibbs free energy of the formation indicated the spontaneous partition process in the micellar systems.     

The effect of NaOH on dodecyltrimethylammonium hydroxide aggregation in aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) in aqueous NaOH solutions was studied as a function of NaOH concentration. As in NaOH-free DTAOH aqueous solutions, the surfactant underwent a stepwise aggregation mechanism. Changes in the structure of aggregates produced an increase of the concentration at which premicellar aggregates could solubilize hydrophobic dyes and also in the concentration at which hydroxide inons join the aggregates.     

A proton NMR study on aggregation of cationic surfactants in water: effects of the structure of the headgroup

 ¹H NMR chemical shifts of solutions of the following cationic surfactants in D₂O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride, CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δ_mon and the micelle δ_mic. ¹H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant solutions in H₂O, allowing for the difference in structure between D₂O and H₂O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH₂ group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol^-1. Values of (δ_mic–δ_mon) for the surfactant groups at the interface, e.g., CH₃–(CH₂)₁₅–N+(CH₃)₂ and within the micellar core, e.g., CH₃–(CH₂)₁₅–N⁺ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl, and CDPhPrACl. Received: 23 February 1996 Accepted: 29 August 1996     

Effect of compressed CO2 on the critical micelle concentration and aggregation number of AOT reverse micelles in isooctane

The effect of compressed CO2 on the critical micelle concentration (cmc) and aggregation number of sodium bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles in isooctane solution was studied by UV/Vis and fluorescence spectroscopy methods in the temperature range of 303.2-318.2 K and at different pressures or mole fractions of CO2 (X(CO2)). The capacity of the reverse micelles to solubilize water was also determined by direct observation. The standard Gibbs free energy (DeltaGo(m)), standard enthalpy (DeltaHo(m)), and standard entropy (DeltaSo(m)) for the formation of the reverse micelles were calculated by using the cmc data determined. It was discovered that the cmc versus X(CO2) curve and the DeltaGo(m) versus X(CO2) curve for a fixed temperature have a minimum, and the aggregation number and water-solubilization capacity of the reverse micelles reach a maximum at the X(CO2) value corresponding to that minimum. These results indicate that CO2 at a suitable concentration favors the formation of and can stabilize AOT reverse micelles. A detailed thermodynamic study showed that the driving force for the formation of the reverse micelles is entropy.     

Enthalpy-entropy compensation in micellization of sodium dodecyl sulphate in water/methanol,water/ethylene glycol and water/glycerol binary mixtures

The enthalpy-entropy compensation in micellization of sodium dodecyl sulphate (SDS) in binary mixtures of water/methanol (MeOH), water/ethylene glycol (EG) and water/glycerol (GL) over a temperature range of 10–60°C was examined. When the cosolvent concentration was low, the critical micelle concentration (CMC) depended only on the total amount of the hydroxyl group added. When the cosolvent concentration was high, the increase in CMC followed the sequence: MeOH>EG>GL. Enthalpy and entropy changes were evaluated from which the compensation temperature was determined. Both enthalpy and entropy changes decreased on the addition of the cosolvents, indicating a lowering of solution hydrophobicity. The compensation temperature was found as a constant over the cosolvent concentration range, as a result, was not a good index for characterizing the solute/solvent interactions. The two reference temperatures at which the enthalpy-entropy change respectively became zero were strongly influenced by the cosolvent addition, therefore could serve as a proper index for solution hydrophobicity.     

Reactivity of supramolecular systems based on calix[4]resorcinarene derivatives and surfactants in hydrolysis of phosphorus acid esters

The formation of mixed micelles of amphiphilic calix[4]resorcinarenes with aminomethyl (AMC, PAMC), tris(hydroxymethyl)amide (THAC) fragments and the cationic surfactant cetyl trimethylammonium bromide (CTAB) in water and aqueous DMF solutions (10-50% DMF) leads to the decrease of the critical micelle concentration of the systems and the increase of the size of the mixed micelles in comparison with CTAB micelles. The catalytic activity of the mixed systems in the hydrolysis of phosphorus acid esters is higher than those of CTAB micelle and AMC, PAMC or THAC aggregates.     

Micellization of polystyrene-graft-poly(ethylene oxide) and its mixtures with polystyrene homopolymer in ethanol

Micellization behaviors of polystyrene-graft-poly(ethylene oxide) (PS-graft-PEO) and its mixtures with PS homopolymer in ethanol were investigated by means of nuclear magnetic resonance (¹H NMR) spectroscopy, transmission electron microscopy (TEM), and viscometry. It was revealed that PS-graft-PEO could self-assemble to form polymeric micelles with a core-shell structure in the shape of spherical. Micelle formation of PS-graft-PEO in ethanol was strongly dependent on the concentration, temperature, and the PS chain contents in PS-graft-PEO. The introduction of PS homopolymer not only decreases the critical micelle concentration, but also changes the morphology of the micelles.     

Determination of critical micelle concentration of bile acid salts by micro-calorimetric titration

Critical micelle concentrations (CMC) of sodium salts of cholic, deoxycholic and chenodeoxycholic acids in phosphate buffer (pH 7.92) have been determined from microcalorimetric titration curves. The obtained values of 18.4±0.6, 5.3±0.2 and 7.0±0.2 mM, respectively, for Na cholate, Na deoxycholate and Na chenodeoxycholate are close to literature values obtained by other methods. CMC values for secondary micelles were also obtained. This microcalorimetric titration method gives highly reproducible results and rapid determination of CMC values of bile acid salts.     

Determination of the critical premicelle concentration, first critical micelle concentration and second critical micelle concentration of surfactants by resonance Rayleigh scattering method without any probe

The purpose of this work is to determine the values of critical premicelle concentration (CPMC), first critical micelle concentration (FCMC) and second critical micelle concentration (SCMC) of surfactants using a common spectrofluorophotometer by recording resonance Rayleigh scattering (RRS) signal without any probe. The plot of the RRS intensities at the maximum scattering wavelength (I(RRS)(max)) versus surfactant concentrations (c) was constructed to obtain the I(RRS)(max)-c curve. From the inflexions in I(RRS)(max)-c curve, the CPMC, FCMC and SCMC values of a surfactant can be obtained sensitively. The FCMC of some anionic, cationic and nonionic surfactants such as sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC), Tween-20, and Tween-80 were determined by RRS method and the values are in good agreement with those obtained from conductivity and surface tension measurements and literature values. The CPMC and SCMC of SDS and CTAB were also determined by RRS method respectively and the values conform to literature values too. Furthermore, RRS method can also be used to determine the FCMC of an amphiphilic macromolecule-hemoglobin, whose structure resembles a surfactant. From the experimental results, it is concluded that RRS method can be applied to the simultaneous determination of the CPMC, FCMC and SCMC values in a sensitive, accurate and no probe way.     

支链烷基苯磺酸钠聚集性质的实验与理论研究

以芘为探针、二苯酮为猝灭剂,用稳态荧光法测定了合成的4种链长分别为10、12、14、16碳,苯环均在β位取代的对烷基苯磺酸钠的临界胶团浓度、胶团聚集数和微极性.研究了链长对支链烷基苯磺酸钠聚集性质的影响.分析了支链烷基苯磺酸钠疏水、亲水基团对聚集性质的影响.用量子化学从头算Hartree Fock方法取6 31G 基组计算了支链烷基苯磺酸根离子气相中的电荷分布.     

聚肽-壳聚糖复合体系的自组装行为研究

以聚肽、壳聚糖为原料,制备复合纳米粒子,采用透射电镜、动态激光散射仪及Zeta电位分析仪、荧光光谱仪对制备成的聚肽-壳聚糖复合体系纳米粒子的形貌、粒径、Zeta电位及临界胶束浓度等自组装行为进行表征,结果表明:聚肽-壳聚糖复合体系纳米粒子是具有壳-核结构的球型粒子;纳米粒子平均粒径为240nm,粒径分布较均匀,稳定性较好;复合体系中聚肽的临界胶束浓度为4.55×10-4mg/mL.     

Comparison of block-copolymer with soap in micelle formation

Simple equations for the micelle formation of block-copolymers are derived from the concept of Leibler-Orland-Wheeler. The size of micelle, core, and corona are expressed in terms of chain length of block-copolymers and homopolymers and the interaction parameters of the components based on the balance between the interface energy and the strain energy of the polymer chains. These equations are extended to the soap micelle by taking the electric repulsion of soap ions into consideration. Various data on the micelle size, the solubility, the critical micelle concentration, the critical solution temperature, and the salt effect can be explained quantitatively by the theory. The solubilization ability is also discussed.     

Determination of critical micelle concentrations and aggregation numbers by fluorescence correlation spectroscopy: aggregation of a lipopolysaccharide

Fluorescence correlation spectroscopy (FCS) is often used to determine the mass or radius of a particle by using the dependence of the diffusion coefficient on the mass and shape. In this article we discuss how the particle size of aggregates can be measured by using the concentration dependence of the amplitude of the autocorrelation function (ACF) instead of the temporal decay. We titrate a solution of aggregates or micelles with a fluorescent label that possesses a high affinity for these structures and measure the changes in the amplitude of the ACF. We develop the theory describing the change of the ACF amplitude with increasing concentrations of labels and use it to fit experimental data. It is shown how this method can determine the aggregation number and critical micelle concentration of a standard detergent nonaethylene glycol monododecyl ether (C₁₂E₉) and a lipopolysaccharide (LPS: Escherichia coli 0111:B4).     

稳态荧光探针法研究Ca2+与十二烷基苯磺酸钠的相互作用

用稳态荧光探针法研究了Ca2+与十二烷基苯磺酸钠(SDBS)的相互作用.研究发现,Ca2+与SDBS在一定条件下产生沉淀.将芘探针溶在有沉淀体系中所测得的第一峰荧光强度I1与第三峰荧光强度I3之比(I1/I3)的大小随表面活性剂浓度变化的突变点与用透光率法测得的沉淀点相对应;将沉淀体系离心,把芘溶在离心后所得的上清液中,此时所测得的I1/I3值随表面活性剂浓度变化的突变点则与透光率法测得的沉淀开始溶解的点相对应.且随着盐的加入及盐浓度的增加,芘的I1/I3值减小.在相同盐浓度下,二价金属盐比一价金属盐对芘的I1/I3值影响大.     

Role of a Surface Active Agent in the Sol-Emulsion-Gel Synthesis of Spherical Alumina Powders

Spheroidal alumina particles of tailor-made size were prepared by the sol-emulsion-gel method under simultaneous mechanical agitation and sonication and by systematic variation of the concentration of a non-ionic surfactant in the organic solvent (oil phase) above or below the critical micelle concentration (CMC). The CMC of the surfactant in the organic solvent of low dielectric constant was determined from discernible breaks in surface tension, viscosity, optical absorption and dye fluorescence vs. concentration curves. The CMC of the surfactant played an important role in controlling the sol droplet size and accordingly, the size of the alumina particles obtained therefrom. Transmission electron microscopy (TEM) revealed that near (but below) CMC the nanospheroids (10–50 m) were in the state of chain-like agglomerates. Beyond CMC, spheroidal particles of larger dimensions were obtained. Particle size analysis showed a sharp decrease in mean size with increasing concentration of the surfactant up to CMC, above which a gentle upward trend was noticed.