Solubilization surfactant systems

Surface activity is not limited to aqueous systems, however. AH of the combiaations of aqueous and nonaqueous phases are known to occur, but because water is present as the solvent phase in the overwhelming proportion of commercially important surfactant systems, its presence is assumed in much of the common terminology of industry. Thus, the water-soluble amphipathic groups are often referred to as solubilizing groups. 

Ci2-Ci3 ether carboxylic acid with 4.5-6 mol EO and Ci2-C15 ether carboxylic acid with 9 mol EO as cosurfactant improve the use of alkyl-o-xylene-sulfonate as primary surfactant at different salinity while maintaining good oil solubilization [189]. It is possible to optimize the surfactant system in relation to the crude oil reservoir characteristics. 

A. T. Florence, Drug Solubilization in Surfactant Systems, in Techniques of Solubilization of Drugs (S. H. Yalkowsky, ed.), Marcel Dekker, New York, 1981, pp. 15-89. 

This overview will outline surfactant mixture properties and behavior in selected phenomena. Because of space limitations, not all of the many physical processes involving surfactant mixtures can be considered here, but some which are important and illustrative will be discussed these are micelle formation, monolayer formation, solubilization, surfactant precipitation, surfactant adsorption on solids, and cloud point Mechanisms of surfactant interaction will be as well as mathematical models which have been be useful in describing these systems,... 

In this paper, we report the solution properties of sodium dodecyl sulfate (SDS)-alkyl poly(oxyethylene) ether (CjjPOEjj) mixed systems with addition of azo oil dyes (4-NH2, 4-OH). The 4-NH2 dye interacts with anionic surfactants such as SDS (11,12), while 4-OH dye Interacts with nonionic surfactants such as C jPOEn (13). However, 4-NH2 is dependent on the molecular characteristics of the nonionic surfactant in the anlonlc-nonlonic mixed surfactant systems, while in the case of 4-OH, the fading phenomena of the dye is observed in the solubilized solution. This fading rate is dependent on the molecular characteristics of nonionic surfactant as well as mixed micelle formation. We discuss the differences in solution properles of azo oil dyes in the different mixed surfactant systems. 

Micellar and pre-micellar solutions of methanol in triolein were studied with three different surfactant systems using 2-octanol as a co-surfactant. Surfactants evaluated by viscosity, conductivity, density, refractive index and particle size data along with polarizing microscopic examinations were bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate. Data show phase equilibria regions of liquid crystalline phases as well as micellar solutions. All systems were effective for solubilizing methanol in triolein. The order of effectiveness for water tolerance is Tetradecyldimethylammonium linoleate>... 

Micelles are often present in surfactant systems. In some processes, such as solubilization, they are directly involved. Micelles indirectly affect many other processes because monomer concentrations or activities of the surfactant components are dictated by the monomer— micelle equilibrium at total surfactant concentrations above the CMC. Therefore, interest in mixed micelle formation will continue to grow. 

In the real world, soluble organic materials may be present in the aqueous surfactant system. As with micelles, it is important to know how these affect mixed admicelle formation and how well these organics are solubilized in the admicelle (adsolubi1ized). 

This product is an aqueous solution of water-soluble vitamins with oily vitamin A palmitate and cholecalceferol solubilized in water using the surfactant system of Tween 80 and Cetomacrogol. This syrup is a solubilized oil surfactant system and is liable to heat and rate of mixing. The temperature of solution must not exceed 30°C at the time of final mixing. The final mixing must be in continuous manner without any interruption. For the preparation of oily phase, the container must be dry. 

In this study it is the homogeneous micellar phases that comprise the microemulsions. For this 5% surfactant system it is only over a relatively narrow range of temperatures that it is possible to have fairly extensive solubilization of either oil or water in the micellar solutions. 

Florence (1983) provide a comprehensive reference for the use of surfactants in drug formulation development. The treatment by Florence (1981) of drug solubilization in surfactant systems is more focused on the question at hand and provides a clear description of surfactant behavior and solubilization in conventional hydrocarbon-based surfactants, especially nonionic surfactants. This chapter will discuss the conventional surfactant micelles in general as well as update the reader on recent practical/commercial solubilization applications utilizing surfactants. Other uses of surfactants as wetting agents, emulsiLers, and surface modiLers, and for other pharmaceutical applications are nc emphasized. Readers can refer to other chapters in this book for details on these uses of surfactant Polymeric surfactant micelles will be discussed in Chapter 13, Micellization and Drug Solubility Enhancement Part II Polymeric Micelles. 

It has been well documented that surfactants self-associate in aqueous solution to minimize the are of contact between their hydrophobictails and the aqueous solution (Mukerjee, 1979 Tanford, 1980). This phenomenon occurs at a critical concentration of surfactant, the critical micelle concentration or CMC (see Figure 12.4) above where the surfactant molecules exist predominantly as monomeric units and above which micelles exist. The CMC can be measured by a variety of techniques, for example, surface tension, light scattering, osmometry, each of which shows a characteristic break point in the plot of the operative property as a function of concentration. Knowing the CMC of the particular surfactant system and understanding the conditions that may raise or lower that critical concentration is important to the design of a formulation based on micellar solubilization. 

Micellar Solubilization and Other Physicochemical Parameters for Binary Mixed Surfactant Systems... 

Treiner, C., M. Nortz, C. Vaution, and F. Puisieux. 1988. Micellar solubilization in aqueous binary surfactant systems Barbituric acids in mixed anionjcnonionic or cationiGf nonionic mixturesJ. Coll. Interf. 

R. Leung and D. O. Shah. Solubilization and phase-equilibria of water-in-oil microemulsions. 2. Effects of alcohols, oils, and salinity on single-chain surfactant systems. J. Colloid Interface Sci., 120(2) 330-344, 1987. 

Enhanced HOC solubility in surfactant systems generally has been quantified by a distribution coefficient that only considers HOC partitioning to surfactant micelles that exist above the critical micelle concentration (CMC). Although surfactants can form a mobile micellar pseudophase that leads to the facilitated transport of solubilized HOCs, they also can be adsorbed by the solid matrix and thereby lead to HOC partitioning to immobile sorbed surfactants and, thus, enhanced HOC retardation. Therefore, the effectiveness of a remediation scheme utilizing surfactants depends on the distribution of an HOC between immobile compartments (e.g., subsurface solids, sorbed surfactants) and mobile compartments (e.g., water, micelles). 

Peters and Luthy (1993, 1994) performed a detailed analysis of the equilibrium behavior of solvent coal tar water mixtures in work that was complementary to column studies performed by Roy, et. al. (1995). Peters and Luthy successfully modeled ternary phase diagrams of coal tar/n-butylamine/water systems. In addition, Peters and Luthy identified n-butylamine as the leading solvent for coal tar extraction. Pennell and Abriola (1993) report the solubilization of residual dodecane in Ottawa sand using a nonionic surfactant, polyoxyethylene sorbitan monooleate, which achieved a 5 order of magnitude increase over the aqueous solubility, but is still 7 times less than the equilibrium batch solubility with the same surfactant system. 

Figure 7. Plots of hexadecane removal percentage as micellarly solubilized, middle phase microemulsified. and free phase against the number of flushed surfactant system pore volumes. Also plotted is the effluent concentration of micellarly solubilized oil.

We began the batch squalane extraction studies by mixing 30 mis of the middle phase from the surfactant system 10% SDBS/17% IPA/12.4% NaCl/dodecane (Figure 6) with 30 mis. of squalane. The solutions were mixed for 10 minutes on a wrist action shaker and allowed to separate. Coalescence was rapid and complete in 5 minutes. The squalane rich phase was separated, and both phases were analyzed for dodecane and SDBS by the methods described previously. These results are summarized in Table V. The batch study was encouraging since 98% of the original solubilized dodecane from Figure 6 (12.4% NaCl ) partitioned into squalane. All the surfactant remained in the aqueous phase, as expected. 

The surfactant system AOT/TWEEN 80 removed 99.4% of residual hexadecane from glass beads in 4.7 pore volumes with a total of 49.6% recovered as free phase, 31.1% recovered as micellarly solubilized, and 18.7% recovered as microemulsified in the middle phase. These results demonstrate the potential efficiency of supersolubilization (i.e., enhanced solubilization as the type I-III boundary is approached), and mobilization (even if just into the type III system but not yet optimal) in expediting extraction of hydrophobic NAPLs. 

For many simple surfactant systems, the methods of electron and fluorescence spectroscopy are not directly applicable, but in quite a few cases either the surfactant or a solubilized molecule displays useful light absorbing and/or fluorescing properties. However, it is more frequently so that measurements are made on a spectroscopic probe added in small amounts to the system of interest. 

The solubilization phenomenon, which refers to the dissolution of normally insoluble or only slightly soluble compounds in water caused by the addition of surfactants, is one of the most striking effects encountered for surfactant systems. Solubilization is of considerable physico-chemical interst, such as in discussion of the structure and dynamics of micelles and of the mechanism of enzyme catalysis, and has numerous practical applications, such as in detergency, in pharmaceutical preparations and in micellar catalysis. In biology, solubilization phenomena are most significant, e.g., cholesterol solubilization in phospholipid bilayers and fat solubilization in fat digestion and transport. 

The very complex variation of the amount solubilized, as well as physico-chemical properties, with chemical structure of solubilizate and surfactant as well as with surfactant concentration cannot be adequately discussed solely in terms of the energetical conditions of the solubilizate in the micelles. Thus one should also consider the conditions in the phase which separates out at the solubilization limit this is in most cases a liquid crystalline phase. A fundamental basis for a proper understanding of solubilization in surfactant systems is, therefore, a detailed information on phase equilibria in three-component systems surfactant-solubilizate-water. Due in particular... 

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