Micellar solution surfactants

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

One of trends of development of thin-layer chromatography implies that replacement of aqueous-organic eluents by micellar surfactants solution. This is reduces the toxicity, flammability, environmental contamination and cost of the mobile phases, reduce sample prepar ation in some cases. 

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

This technique of MEUF has also been successfully employed for the recovery of thuringiensin [258], removal of cresols [262], extraction of chromate anion [257], removal of dissolved organic pollutants [256], removal of -alcohols [263],preconcentration and removal of iron [260], and preconcentration of aniline derivatives [261].Kandori and Schechter [264] have given a detailed account of selecting surfactants for MEUF. The design characteristics of micellar enhanced utrafilters and cross-flow ultrafiltration of micellar surfactant solutions have been described by Markets et al. [265]. 

The utility of FTIR spectroscopy in studies of phase transitions involving micellar surfactant solutions has been increasingly demonstrated in recent years (1-7). The familiar concentration-dependent monomer to micelle transition (cmc), the thermally induced hydrated solid to micelle transition (cmt), and the micelle to coagel transition achieved at high pressure (ccp) have all been investigated (Figure 1). These transitions can be monitored by shifts in frequency (= 5 cm"1) of the CH2 stretching bands which appear in the spectra. 

Only relatively small shifts of these bands ( > 1 cm 1) as a function of concentration or temperature are observed in the spectra of micellar surfactant solutions in the absence of the transitions mentioned above. It has therefore been... 

The model outlined predicts the equilibrium distribution of HOC in a closed system of soil and micellar surfactant solution as a function of surfactant dose. The model requires values for the parameters Km, /., CMC, Kd,... 

The depletion interaction is present always when a film is formed from micellar surfactant solution the micelles play the role of the smaller particles. At higher micellar concentrations, the volume exclusion interaction becomes more complicated it follows the oscillatory curve depicted in Figure 5.26. In this case only, the first minimum (that at ft —> 0) corresponds to the conventional depletion force. 

Danov, K.D., Adsorption from micellar surfactant solutions nonlinear theory and experiment, J. Colloid Interface ScL, 183, 223, 1996. 

Based on these studies, the utilization for surfactants as a soil-washing agent appears to be a promising strategy for many future site remediations. Figure 3 illustrates three conceptual systems that will aid the description of the physicochemical concepts of CAD partitioning in the systems of soil and micellar surfactant solution. 

The amount of substance present in the micellar state, cmjc = mnmic / NA may exceed the concentration of it in the molecular solution by several orders of magnitude. The micelles thus play a role of a reservoir (a depot) which allows one to keep the surfactant concentration (and chemical potential) in solution constant, in cases when surfactant is consumed, e.g. in the processes of sol, emulsion and suspension stabilization in detergent formulations, etc. (see Chapter VIII). A combination of high surface activity with the possibility for one to prepare micellar surfactant solutions with high substance content (despite the low true solubility of surfactants) allows for a the broad use of micelle-forming surfactants in various applications. 

At high surfactant concentrations (i.e., much above the CMC), thin foam films were observed (48—53) to become thinner in a stepwise fashion that is, thinning foam films formed from micellar surfactant solutions exhibit a number of metastable states before attaining an equilibrium film thickness. This process can be followed in Figure 13, which shows a photocurrent (film thickness)—time interferogram of a horizontal flat film... 

Polymer Synthesis. Copolymers of alkylacrylamide (R) and acrylamide (AM), which we called RAM, were prepared with a micellar polymerization technique (4). A micellar surfactant solution was used to disperse the hydrophobic alkylacrylamide monomer into an aqueous phase that contained acrylamide. The monomers were polymerized with a standard free-radical initiator (e.g., potassium persulfate) or a redox initiator to yield the desired random copolymer. Varied temperature and initiator concentrations were used to provide polymers of different molecular weights. Polymerizations were taken to essentially complete conversion. Compositions, in terms of hydrophobe level reported in this chapter, were based on amounts charged to the reactor. Further details on the synthesis and structure of these RAM polymers... 

The equilibrium and dynamics of adsorption processes from micellar surfactant solutions are considered in Chapter 5. Different approaches (quasichemical and pseudophase) used to describe the micelle formation in equilibrium conditions are analysed. From this analysis relations are derived for the description of the micelle characteristics and equilibrium surface and interfacial tension of micellar solutions. Large attention is paid to the complicated problem, the micellation in surfactant mixtures. It is shown that in the transcritical concentration region the behaviour of surface tension can be quite diverse. The adsorption process in micellar systems is accompanied by the dissolution or formation of micelles. Therefore the kinetics of micelle formation and dissociation is analysed in detail. The considered models assume a fast process of monomer exchange and a slow variation of the micelle size. Examples of experimental dynamic surface tension and interface elasticity studies of micellar solutions are presented. It is shown that from these results one can conclude about the kinetics of dissociation of micelles. The problems and goals of capillary wave spectroscopy of micellar solutions are extensively discussed. This method is very efficient in the analysis of micellar systems, because the characteristic micellisation frequency is quite close to the frequency of capillary waves. 

Recently a new field, mesoscopic physics, has emerged. It is interesting to understand the physical properties of systems that are not as small as a single atom, but small enough that the properties can be dramatically different from those in a larger assembly. All these new mesoscopic phenomena can easily be observed in the dielectric properties of colloid systems. Their properties strictly depend on the dimensional scale and the time scale of observation. Self-assembling systems such as micellar surfactant solutions, micro emulsions, emulsions, aqueous solutions of biopolymers, and cell and lidposome suspensions all to-... 

Emulsions are often prepared from micellar surfactant solutions. As known, above a given critical micelle concentration (cmc) siufactant aggregates (micelles) appear inside the surfactant solutions. At rest the micelles exist in equilibrium with the surfactants monomers in the solution. If the concentration of the monomers in the solution is suddenly decreased, the micelles release monomers until the equilibrium concentration, equal to cmc, is restored at the cost of disassembly of a part of the micelles (63, 64). 

In the case of small Brownian deformable droplets the interaction energy, when the continuous phase is a micellar surfactant solution of sodium nonylphenol polyoxy-ethylene-25 (SNP-25S), is illustrated in Fig. 8 as a function of the thickness, A, and film radius, R (see Fig. 3 for the definition of the geometry). The parameters of the micro-emulsion system are R = 2 im, d = 9.8 nm, (j> = 0.38, Ah = 5x10" J, <7= 7.5 mN/m, % = -135 mV, r = 1.91 nm, the electrolyte concentration 25 mM. The points on the contour plot (Fig. 8) correspond to tree local minima of -406 AbT, -140 k T and -37 k T corresponding to film containing 0, 1 and 2 micellar layers, respectively (Ivanov et al. 1999). These three possible films are thermodynamically stable and they act like barriers against the closer approach and flocculation (or coalescence) of the droplets in emulsions. 

Surfactant adsorption on the thin layer support cannot be avoided. It is the cause of a micellar gradient concentration between the solvent front and the mobile phase reservoir. Adsorption up to saturation of the sorbent depletes the surfactant concentration in the mobile phase. A double solvent front was observed, the upper one was a dilute non micellar surfactant solution, the lower second front corresponded to the micellar front [22-25, 27]. The problem is that this phenomenon introduces potential error in the identification of the exact Rf parameters of the solutes, inducing accuracy concerns of the K coefficients [28]. This adsorption-induced micellar concentration gradient was used to separate the polar solutes in the nonmicellar region (between the two solvent fronts) from the hydrophobic solutes separated by the slow moving micellar phase [22,27]. 

Kriegel, C., Kit, K.M., McClements, D.J., and Weiss, J. (2009) Electrospinning of chitosan-poly (ethylene oxide) blend nanofibers in the presence of micellar surfactant solutions. Polymer, 50, 189-200. 

Vlahovska, PM., Horozov, T., Dushkin, CD., Kralchevsky, P.A., Mehreteab, A., and Broze, G., Adsorption from micellar surfactant solutions nonlinear theory and experiment, J. Colloid Interface Sci., 183, 223, 1997. 

This involved the use of a micellar surfactant solution to disperse the hydrophobic alkylacrylamide monomer into an aqueous phase containing acrylamide. The monomers were polymerized using a standard free radical initiator such as potassium persulfate or a redox initiator to yield the desired random copolymer. Further details on the synthesis and structure of these RAM polymers can be found elsewhere. 

A traditional property of micellar surfactant solutions is their ability to dissolve water-insoluble, oil-soluble materials such as hydrocarbons, esters, and certain dyes and perfumes. This property, in fact, gave early support to the concept that micelles do indeed exist in aqueous solutions of surfactants, the core of the micelles in effect providing microdroplets of liquid hydrocarbon in solution with solvent properties. 

Dynamics of Adsorption from Micellar Surfactant Solutions.276... 

Differential interferometry in reflected light allows for the measurement of the shape of the upper reflecting snrface. This method was nsed by Nikolov et al. [253,273-275] to determine the contact angle, film, and line tension of foam films formed at the top of small bubbles floating at the surface of ionic and nonionic surfactant solntions. An alternative method is the holographic interferometry applied by Picard et al. [276,277] to study the properties of bilayer lipid membranes in solution. Film contact angles can also be determined from the Newton rings of liquid lenses, which spontaneously form in films from micellar surfactant solutions [217],... 

Bergeron, Langevin, and coworkers [52, 75, 76, 83-85] have made an extensive study of the spreading of PDMS oils on the surfaces of micellar surfactant solutions but have mainly confined their observations to two oils with respective molecular weights of 10 and 2.5 x 10 . Surfactants included AOT and homologues of alkyl trimethylammonium bromides. It is noteworthy that the spreading pressure of... 

Spreading Pressures, Entry, and Spreading Coefficients for Polydimethylsiloxane Oils on Aqueous Micellar Surfactant Solutions... 

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