Determining the Critical Micelle Concentration in O/W Emulsion Using the Rate Constant of Hydrolysis for Benzyl Acetate

An attempt to evaluate the kinetically effective critical micelle concentration CMC of sodium dodecyl sulfate (SDS) in micellar solutions and in O/W emulsions at 40°C and pH 9 utilizing the pseudo first order rate constant of benzyl acetate hydrolysis was implemented. The critical micelle concentration of SDS in micellar solutions was determined by both surface tension measurements utilizing Wilhelmy plate technique and by rate constant of hydrolysis. Hydrolysis reaction of benzyl acetate was monitored in surfactant solutions as well as in o/w emulsions as a function of time. Emulsion droplets were controlled using microfluidizer 110 T and oily droplets were separated from the emulsion by ultracentrifugation at (11,500 rpm or 9,800 g) prior to analysis by high performance liquid chromatography. The value of the critical micelle concentration (CMC) in micellar solutions in the presence of benzyl acetate as determined from the Wilhelmy plate technique was 7.8 × 10^?4 moles/L (CMC in micellar solution was 10 times lower than the value in literature due to use of buffer) while the CMC as determined from the kinetic study was 8.8 × 10^?4 moles/L. In emulsion systems, using 5% mineral oil, the CMC value was 8.6 × 10^?3 moles/L and at 10% oil, the value doubled to 1.73 × 10^?2 moles/L. The above results indicate that kinetics can be used to determine CMC in micellar solutions and in o/w emulsions.     

Boltzmann distributions and slow relaxation in systems with spherical and cylindrical micelles

Equilibrium and nonequilibrium distributions of molecular aggregates in a solution of a nonionic surfactant are investigated at the total surfactant concentration above the second critical micelle concentration (CMC2). The investigation is not limited by the choice of a specific micellar model. Expressions for the direct and reverse fluxes of molecular aggregates over the potential humps of the aggregation work are derived. These aggregation work humps set up activation barriers for the formation of spherical and cylindrical micelles. With the aid of the expressions for molecular aggregate fluxes, a set of two kinetic equations of micellization is derived. This set, along with the material balance equation, describes the molecular mechanism of the slow relaxation of micellar solution above the CMC2. A realistic situation has been analyzed when the CMC2 exceeds the first critical micelle concentration, CMC1, by an order of magnitude, and the total surfactant concentration varies within the range lying markedly above the CMC2 but not by more than 2 orders of magnitude. For such conditions, an equation relating the parameters of the aggregation work of a cylindrical micelle to the observable ratio of the total surfactant concentration and the monomer concentration is found for an equilibrium solution. For the same conditions, but in the nonequilibrium state of materially isolated surfactant solution, a closed set of linearized relaxation equations for total concentrations of spherical and cylindrical micelles is derived. These equations determine the time development of two modes of slow relaxation in micellar solutions markedly above the CMC2. Solving the set of equations yields two rates and two times of slow relaxation.     

Counter-current chromatography using hexane/surfactant-containing water solvent systems

We developed a n-hexane/surfactant-containing water solvent system in counter-current chromatography (CCC) in order to separate hydrophobic compounds. By using the upper phase as the mobile phase, we have separated steroid samples. Retention times of steroids progesterone and delta4-androstene-3,17-dione increased slightly by increasing the concentration below the critical micellar concentration (CMC) of surfactant sodium 1-heptanesulfonate. However, the retention times increased drastically while the SHS concentrations were above the CMC. The partition of these two steroids in the two phases was significantly dependent on the interaction with micelles. Aromatic hydrocarbons were not retained by the lower phase no matter what the surfactant concentrations were. Their hydrophobic interaction with n-hexane greatly exceeded that with the micellar solution. The retention times of esters, however, were only slightly affected by the surfactant addition even above the CMC. The weaker interaction between esters and the micellar solution was probably due to their higher polarity. The micellar solvent systems provide an alternative way for hydrophobic sample separations in CCC, but the performance is limited.     

Mesoscopic simulation of self-assembly in surfactant oligomers by dissipative particle dynamics

Self-assembling properties of surfactant oligomers in an aqueous medium is simulated by dissipative particle dynamics (DPD). The critical micellar concentration (CMC) of dimeric (oligomerization = 2) and trimeric (oligomerization = 3) surfactant is much lower than their single-chain counterpart. All surfactants form spherical micelles at the concentration not far above their CMC. The transition from spherical to cylindrical micelles exhibits with increasing surfactant concentration. Lamellar micelles will appear with further increasing the surfactant concentration. For dimeric and trimeric surfactants, cylindrical micelles transform into extremely long “wormlike” or “threadlike” micelles before the transition to lamellar micelles. These results are in qualitative agreement with laboratory experiment. Average aggregation numbers (AN) of micelles increase with a power law of AN  c when the surfactant concentration c CMC. The self-diffusion coefficients will drop with a power law of D  c⁻ when wormlike micelles are formed.     

Determination of critical micelle concentrations of ionic and nonionic surfactants based on relative viscosity measurements by capillary electrophoresis

The critical micelle concentration (CMC) can be obtained by measuring the distinct physical properties of surfactant molecules in the monomeric and micellar states. In this study, two linear increments of relative viscosity with distinct slopes were obtained when increasing surfactant concentrations from dilute solution to above the CMC, which was then determined by the intersection of the two linear extrapolations. Using a capillary electrophoresis (CE) instrument and Poiseuille’s law, the viscosities of surfactants at a series of concentrations covering the monomeric and micellar regions could be obtained by measuring the hydrodynamic flow rates of the corresponding surfactant solutions. We applied this method to determine the CMC values of various types of surfactants including anionic, cationic, zwitterionic, and nonionic surfactants. The resulting CMC values were all in good agreement with those reported in literature. Using this method, the multiple-stage micellization process of a short-chain surfactant was revealed. We have also demonstrated that the CE-based viscometer was applicable to the study of CMC variation caused by organic or electrolyte additives.     

A photophysical study of the urea effect on micellar properties of sodium dodecylsulfate aqueous solutions

With the aim of studying the effect of urea on micellar properties of aqueous solutions of sodium dodecylsulfate (SDS), steadystate fluorescence experiments were carried out with different luminescence probes incorporated into the micellar phase. The increase of critical micelle concentration (CMC) of the surfactant with urea addition was followed by changes in the relative intensities of the vibrational fine structure of the pyrene fluorescence spectra. Micellar aggregation numbers were obtained from the analysis of fluorescence quenching data using ruthenium tris(bipyridyl) chloride and 9-mehylanthracene as a donorquencher pair. It was found that the decrease in the aggregation number is mainly controlled by rise in the surface area per headgroup of the surfactant. From fluorescence measurements, using several ionic probes (8-anilino-1-naphthalen-sulfonic acid, rhodamine B, and auramine O), it was found that urea decreases the polarity and increases the microviscosity of the micellar interface. These effects, which are dependent on the concentration of urea, can be explained according to a direct interaction of urea at the micellar surface.     

Determination of the Critical Micelle Concentration of Cationic Surfactants by Capillary Electrophoresis

The determination of the critical micelle concentration (CMC) of cationic surfactants by capillary electrophoresis was demonstrated. In this study, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DoTAB) were selected as cationic surfactants and propazine was chosen as test solute. In the evolution of the effective electrophoretic mobility of propazine as a function of surfactant concentration, a dramatic change in slope at a particular concentration is a good indication of the CMC of this surfactant. The CMC values determined experimentally were further confirmed by a curve-fitting approach. Simulation of the electrophoretic mobility curves as a function of surfactant concentration in both micellar electrokinetic chromatography and capillary zone electrophoresis using cationic surfactants as an electrolyte modifier was performed for propazine, and the intersection of these two mobility curves allowed us to precisely predict the CMC of the surfactant. The CMC values determined for TTAB and DoTAB are 1.6 ± 0.1 and 11.0 ± 0.1 mM, respectively, in the case of an electrolytic solution consisting of 70 mM phosphate buffer at pH 6.0. Moreover, the applicability of the electroosmotic mobility as a parameter for the determination of the CMC was examined.     

Second CMC in surfactant micellar systems

Experimental reports of surfactant systems displaying a second critical micelle concentration (second CMC) have been surveyed. It turns out that surfactant micelles usually show a growth behavior with some typical features. (i) Micelles grow weakly at low surfactant concentrations but may switch to a much stronger growth behavior at higher concentrations. The second CMC is defined as the point of transition from weakly to strongly growing micelles. (ii) Micelles are found to be non-spherically shaped below the second CMC. (iii) At the second CMC micelles are found to be much smaller, with aggregation numbers typically 100–200, than expected for flexible micelles. (iv) Micelles of intermediate size are present in a narrow concentration regime close to the second CMC. (v) Micelles grow much stronger above the second CMC than expected from a sphere-to-rod transition. The conventional spherocylindrical micelle model predicts a smooth growth behavior that contradicts the appearance of a second CMC. Modifying the model by means of including swollen end caps neither account for the presence of micelles with intermediate size, nor the strong growth behavior above the second CMC. Taking into account micelle flexibility is not consistent with the rather low micelle aggregation numbers observed at the second CMC. On the other hand, a recently proposed alternative theoretical approach, the general micelle model, have been demonstrated to take into account basically all features that are typical of experimentally observed micellar growth behaviors.     

Adsorption of nonionic surfactants on cellulose surfaces: adsorbed amounts and kinetics

Kinetic and equilibrium aspects of three different poly(ethylene oxide) alkylethers (C12E5, C12E7, C14E7) near a flat cellulose surface are studied. The equilibrium adsorption isotherms look very similar for these surfactants, each showing three different regions with increasing surfactant concentration. At low surfactant content both the headgroup and the tail contribute to the adsorption. At higher surface concentrations, lateral attraction becomes prominent and leads to the formation of aggregates on the surface. The general shape of the isotherms and the magnitude of the adsorption resemble mostly those for hydrophilic surfaces, but both the ethylene oxide and the aliphatic segments determine affinity for the surface. The adsorption and desorption kinetics are strongly dependent on surfactant composition. At bulk concentrations below the CMC, the initial adsorption rate is attachment-controlled. Above the CMC, the micellar diffusion coefficient and the micellar dissociation rate play a crucial role. For the most hydrophilic surfactant, C12E7, both parameters are relatively large. In this case, the initial adsorption rate increases with increasing surfactant concentration, also above the CMC. For C12E5 and C14E7 there is no micellar contribution to the initial adsorption rate. The initial desorption kinetics are governed by monomer detachment from the surface aggregates. The desorption rate constants scale with the CMC, indicating an analogy between the surface aggregates and those formed in solution.     

Rapid dissolution of vitamin E by using sodium N-lauroylsarcosinate ionic surfactant

Vitamin E is widely used in pharmaceutical, food and cosmetic preparations. This paper discusses methods of preparing a vitamin E emulsion by using sodium N-lauroylsarcosinate (SNLS) ionic surfactant. The amount of vitamin E dissolved in water was analyzed by turbidity and UV absorption measurements. The emulsion droplet size was determined by laser light scattering. Microemulsions with small particle size and high resistance to oxidation in air can be obtained by solubilizing vitamin E in SNLS solution. The dissolution is rapid and the surfactant solution has high solubilization power. At 0.7% surfactant concentration, the saturation value is 1 g vitamin E per gram of surfactant. The micellar dissociation concentration (MDC) of the surfactant can be estimated from a vitamin saturation—surfactant concentration curve. Dissolution mechanisms at different surfactant concentrations are interpreted by use of the MDC and CMC (critical micellar concentration) concepts.     

Sugar latexes as a new type of binder for water-based paint and coating

Sugar latexes based on saccharid derivatives, such as 3-MDG, 1- or 3-MDF and ITDF, have been synthesized in batch and semi-continuous emulsion polymerization. The polymerizations were carried out at 60 or 70°C, initiated by potassium peroxodisulfate, (KPS), in the presence of either ionic or non-ionic surfactant. The effect of the type and concentration of the surfactant and the type of polymerization process on the colloidal and rheological properties was studied. It was found that the particles size increased with using a non-ionic surfactant. Monodisperse particles were obtained by using SDS below its CMC, and smaller polydisperse latexes were observed when the SDS conc. was above the CMC. The latexes exhibit different non-Newtonian flows depending on the solid content and on the additives.     

Adsorption and electrokinetic phenomena in the system solid — micellar solution of a surface-active substance

Summary It has been found that adsorption isotherms describing the adsorption of sodium 4-hexadecyl-oxytolyl2-sulfonate and sodium dodecyl-benzene-4-sulfonate at different solid surfaces revealed maxima at the range of CMC. Similar maxima also occurred on the curves χ/c. Adsorption of the mentioned surface-active substances from micellar solutions at a solid did not lead to establishment of an equilibrium which would result in an adsorption film containing micelles. The decrease in adsorption at a solid in the range of CMC and above it is discussed on the basis of adsorption equilibrium, established between the micelle, the monomer, and the adsorption film. Postmicellar association of the surfactant can result in a minimum on the adsorption isotherm. During adsorption of a surfactant from micellar solutions, solubilization can take place of reaction products of the surfactant and polyvalent inorganic cations or weakly dissociated molecules, in the rangec _eq≧ CMC.

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Zusammenfassung Die Adsorptionsisothermen von Na-HexadecylOxytolyl-2-Sulfonat und Na-Dodecyl-Benzol-4-Sulfonat an verschiedenen festen Oberfl?chen haben im Bereich der CMC ein Maximum. Dieses Maximum wurde auch bei den Abh?ngigkeiten χ/c gefunden. Die Adsorption der untersuchten grenzfl?chenaktiven Stoffe aus ihren mizellaren L?sungen führt nicht zur Bildung eines Adsorptionsfilmes mit eingelagerten Mizellen. Der Abfall der Adsorption der Tensidmoleküle im Bereich der CMC und darüber hinaus wurde aufgrund der Einstellung des Adsorptionsgleichgewichtes zwischen der Mizelle, dem Monomer und dem Adsorptionsfilm diskutiert. Die postmizellare Assoziation der Tensidmoleküle kann die Entstehung eines Minimums auf der Adsorptionsisotherme zur Folge haben. W?hrend der Adsorption des Tensids aus seinen mizellaren L?sungen k?nnen in Bereichenc _eq ≥ CMC wenig dissoziierte Moleküle oder ein Reaktionsprodukt des Tensids mit den mehrwertigen anorganischen Kationen solubilisiert werden.

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With 13 figures and 1 table     

System peaks in micellar electrophoresis: I. Utilization of system peaks for determination of critical micelle concentration

A new way to determine the critical micelle concentration (CMC) based on the mobilities of system peaks is presented. A general approach for the CMC determination is based on the change of the slope or on finding the inflection point in the plot of a physical property of solution as a function of surfactant concentration. The determination of CMC by system peaks in CE utilizes a "jump" instead of a continuous change in the measured quantity. This phenomenon was predicted by the program PeakMaster, which was modified for simulation of micellar systems. The simulation of the steep change in mobilities of the anionic system peaks showing the CMC value was verified experimentally in a set of measurements, where the concentration of the surfactant was varied while the ionic strength was kept constant. The experimental work fully proved our model. A comparative electric current measurement was carried out. The proposed method seems to offer easier CMC determination as compared to the standard methods.     

Binding of sodium dodecyl sulfate and hexaethylene glycol mono-n-dodecyl ether to the block copolymer L64: electromotive force, microcalorimetry, surface tension, and small angle neutron scattering investigations of mixed micelles and polymer/micellar surfactant complexes

The interactions of sodium dodecyl sulfate (SDS) with the triblock copolymer L64 (EO13-PO30-EO13) and hexaethylene glycol mono-n-dodecyl ether (C12EO6) were studied using electromotive force, isothermal titration microcalorimetry, differential scanning microcalorimetry, and surface tension measurements. In certain regions of binding, mixed micelles are formed, and here we could evaluate an interaction parameter using regular solution theory. The mixed micelles of L64 with both SDS and C12EO6 exhibit synergy. When L64 is present in its nonassociated state, it forms polymer/micellar SDS complexes at SDS concentrations above the critical aggregation concentration (cac). The cac is well below the critical micellar concentration (cmc) of pure SDS, and a model suggesting how bound micelles are formed at the cac in the presence of a polymer is described. The interaction of nonassociated L64 with C12EO6 is a very rare example of strong binding between a nonionic surfactant and a nonionic polymer, and C12EO6/L64 mixed micelles are formed. We also carried out small angle neutron scattering measurement to determine the structure of the monomeric polymer/micellar SDS complex, as well as the mixed L64/C12EO6 aggregates. In these experiments, contrast matching was achieved by using the h and d forms of SDS, as well as C12EO6. During the early stages of the formation of polymer-bound SDS micelles, SDS aggregates with aggregation numbers of approximately 20 were found and such complexes contain 4-6 bound L64 monomers. The L64/C12EO6 data confirmed the existence of mixed micelles, and structural information involving the composition of the mixed micelle and the aggregation numbers were evaluated.     

Synthesis and surface active properties of a gemini-type surfactant linked by a quaternary ammonium group

In this study, cationic surfactants having multi-hydroxyl groups were synthesized by the condensation reaction of octadec-9-enyl glycidyl ether and methyl amine followed by the quaternization with dimethyl sulfate. The structure of the product was elucidated by ¹H-NMR and FT-IR. The minimum critical micelle concentration (CMC) and surface tension achieved using C18:1-BHDM surfactant were 1.24?×?10^?4?mol/L and 43.36 mN/m, respectively. The interfacial tensions measured between 1 wt% surfactant solution and n-decane were found to be in the same order of magnitude as those exhibited between micellar solutions and nonpolar hydrocarbon oils. The contact angle measurement result suggests that C18:1-BADM is the best wetting agent among the surfactants tested during this study. It has been observed that the results for foam stability measurement are consistent with those of CMC and contact angle. That is, the percentage of foam volume decrease has been observed to increase with an increase in number of hydroxyl group.     

Effects of Added Surfactant on the Dynamic Interfacial Tension Behavior of Acidic Oil/Alkaline Systems

The effects of a ready-made surfactant (sodium dodecyl sulfate) on the dynamic interfacial tension between a model acidic oil (linoleic acid dissolved in paraffin oil) and various aqueous alkaline (NaOH) systems have been studied using pendant drop tensiometry at surfactant concentrations both below and above the critical micelle concentration (CMC). Below the CMC the added surfactant contributes significantly to a further reduction of interfacial tension of the reacting acid/alkaline system, whereas above the CMC the added surfactant plays an important role in damping the dynamic trends observed for the reactive system alone. Copyright 2001 Academic Press.     

Studies on micelles

Summary It is shown by the absorption intensity that the micellar volume increases continuously from the CMC in wider surfactant concentration range. Considering many experimental results reported, is presented the model of constant particle concentration above the CMC for the aqueous micellar solutions as the first approximation. The qualitative reasons to present this model are mentioned.

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Zusammenfassung Die Absorption weist darauf hin, da? das Mizellvolumen von der CMC in weitem Konzentrationsbereich grenzfl?chenaktiver Substanzen ansteigt. Aus vielen gegebenen Versuchsdaten wird ein Modell konstanter Partikelkonzentration oberhalb der CMC in gleichmizellaren L?sungen als erste N?herung gefolgert. Die qualitativen Gründe für ein solches Modell sind genannt.

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Series IV.Sata, N. andH. Sasaki, Kolloid-Z.153, 41 (1957).

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The author wishes to thank Prof.N. Sata for his encouragement and discussion and Dr.H. Okuyama for general discussion and also the author is indebted to Mr.S. Saito for the purification of octadecyl trimethyl ammonium chloride and to Mr.S. Fukushima for the discussion about stray light.     

Effect of surfactants on the polymerization of acrylamide in aqueous solutions

The polymerization of acrylamide in aqueous surfactant solutions, initiated by potassium persulfate, has been investigated, dilatometry being used to follow the conversion. It has been shown that below the critical micellar concentration (CMC), cationic, anionic and non-ionic surfactants have no effect, while above the CMC only cationic soaps have an effect, lowering both the rate of polymerization and the molecular weight of the resultant polymer.     

Role of the nonionic surfactant Triton X-405 in emulsion polymerization. I. Homopolymerization of styrene

The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813–3825, 1997     

Ceramic membrane ultrafiltration of anionic and nonionic surfactant solutions

The ultrafiltration of two types of surfactants, sodium dodecyl sulfate (SDS, anionic) and Tergitol NP-9 (nonylphenol polyethylene glycol ether, nonionic), using a 20 nm ZrO₂ tubular membrane was investigated. The influence of crossflow velocity, temperature, pressure, and surfactant concentration on the permeate flux, close to and above the critical micelle concentration (CMC), is reported. Permeate flux and surfactant retention were measured in order to evaluate concentration polarization and fouling phenomena, and also the variation of these parameters due to surfactant/membrane interactions. High surfactant retentions (60–70%) were achieved depending on the feed concentration.