Hydrophilicity surfactants

Ethoxylated Anhydrosorbitol Esters. Ethoxylation of sorbitan fatty acid esters leads to a series of more hydrophilic surfactants (Table 19). All hydroxyl groups of sorbitan can react with ethylene oxide. The stmcture of the principal component of a nominal polyoxyethylene (20) sorbitan monostearate illustrates the composition of these products, where w x y z = 20. 

Monoa.lka.nola.mine Condensates. Coco, lauric, oleic, and stearic monoethanolamides and monoisopropanolamides are the principal surfactants ia the monoalkano1 amide group (Table 24). Monoalkanolamides are generally water-iasoluble soHds that are easily solubilized by hydrophilic surfactants. Except for solubiUty and viscosity, properties and uses are similar to the diethanolamides. Manufacturing processes and yields have been described (96). 

Microemulsions or solubilized or transparent systems are very important ia the marketing of cosmetic products to enhance consumer appeal (32,41). As a rule, large quantities of hydrophilic surfactants are required to effect solubilization. Alternatively, a combination of a solvent and a surfactant can provide a practical solution. In modem clear mouthwash preparations, for example, the flavoring oils are solubilized in part by the solvent (alcohol) and in part by the surfactants. The nature of solubilized systems is not clear. Under normal circumstances, microemulsions are stable and form spontaneously. Formation of a microemulsion requires Httle or no agitation. Microemulsions may become cloudy on beating or cooling, but clarity at intermediate temperatures is restored automatically. 

The common concentration of a surfactant used in a formulation varies from 0.05 to 0.5% and depends on the surfactant type and the solids content of the dispersion. In practice, very often combinations of surfactants rather than single agents are used to prepare and stabilize disperse systems. The combination of a more hydrophilic surfactant with a more hydrophobic surfactant leads to the formation of a complex film at the interface. A good example for such a surfactant pair is the Tween-Span system of Atlas-ICI [71]. 

In both cases, overall adsorption and especially that of sulfonate (or "primary surfactant in the composition of most micellar systems used for EOR) are considerably reduced by simply adding a second product having low adsorption characteristics (NP 30 EO in the above example). This is why we have called this strongly hydrophilic surfactant a desorbent. 

Surface-active agents may be added during the processing of films (internal addition) or by surface treatment of the film (external addition). These tend to reduce the surface energy of the film/water droplet interface promoting a continuous film of water thus enhancing transparency. Examples include hydrophilic surfactants, such as sorbitol or glycerol fatty acid mono- or di-esters. 

A synthetic alternative to this is the chemical reduction of metal salts in the presence of extremely hydrophilic surfactants have yielded isolable nanometal colloids having at least 100 mg of metal per litre of water [105], The wide range of surfactants conveniently used to prepare hydrosols with very good redispersibility properties include amphiphilic betaines A1-A4, cationic, anionic, nonionic and even environmentally benign sugar soaps. Table 3.1 presents the list of hydrophilic stabilizers used for the preparation of nanostructured colloidal metal particles, and Table 3.2 shows the wide variety of transition metal mono- and bi-metallic hydrosols formed by this method [105,120],... 

Floras J, Hoover RR (1998) Genetics of the hydrophilic surfactant proteins A and D. Biochim Biophys Acta 1408(2-3) 312-322... 

The procedure chosen for the preparation of lipid complexes of AmB was nanoprecipitation. This procedure has been developed in our laboratory for a number of years and can be applied to the formulation of a number of different colloidal systems liposomes, microemulsions, polymeric nanoparticles (nanospheres and nanocapsules), complexes, and pure drug particles (14-16). Briefly, the substances of interest are dissolved in a solvent A and this solution is poured into a nonsolvent B of the substance that is miscible with the solvent A. As the solvent diffuses, the dissolved material is stranded as small particles, typically 100 to 400 nm in diameter. The solvent is usually an alcohol, acetone, or tetrahydrofuran and the nonsolvent A is usually water or aqueous buffer, with or without a hydrophilic surfactant to improve colloid stability after formation. Solvent A can be removed by evaporation under vacuum, which can also be used to concentrate the suspension. The concentration of the substance of interest in the organic solvent and the proportions of the two solvents are the main parameters influencing the final size of the particles. For liposomes, this method is similar to the ethanol injection technique proposed by Batzii and Korn in 1973 (17), which is however limited to 40 mM of lipids in ethanol and 10% of ethanol in final aqueous suspension. 

The preparation of a ferrofluid emulsions is quite similar to that described for double emulsions. The starting material is a ferrofluid oil made of small iron oxide grains (Fe203) of typical size equal to 10 nm, dispersed in oil in the presence of an oil-soluble surfactant. The preparation of ferrofluid oils was initially described in a US patent [169]. Once fabricated, the ferrofluid oil is emulsifled in a water phase containing a hydrophilic surfactant. The viscosity ratio between the dispersed and continuous phases is adjusted to lie in the range in which monodisperse fragmentation occurs (0.01-2). The emulsification leads to direct emulsions with a typical diameter around 200 nm and a very narrow size distribution, as can be observed in Fig. 1.33. 

D.J. Miller, T. Henning, and W. Grtibein Phase Inversion of W/O Emulsions by Adding Hydrophilic Surfactant—a Technique for Making Cosmetics Products. ... 

Ch = initial concentration of the hydrophilic surfactant in the external water phase... 

In Fig. 6.15b,c, the effect of varying the hydrophilic surfactant concentration from 3 CMC to 10 CMC is illustrated. It is clear from the graph that increasing the hydrophilic surfactant concentration has the effect of accelerating the salt release. 

Figure 7 indicates the phase behavior of SOW systems containing ternary nonionic surfactant mixtures that in turn contain a very hydrophilic surfactant (Tween 60 Sorbitan -i- 20 EO stearate), a very hpophihc surfactant (Span 20 Sorbitan monolaurate), and an intermediate (Tween 85 Sorbitan 20 EO trioleate or Nonylphenol with an average of 5 EO groups). The two intermediate surfactants correspond exactly to an optimum formulation in the physicochemical conditions, i.e., they exhibit three-phase behavior with the system 1 wt. % NaCl brine-heptane-2-butanol. As the intermediate hy-drophihcity surfactant is replaced by an equivalent mixture of the extreme ... 

Salt Negative with increasing salt concentration Effective shielding of the hydrophilic surfactant part reduces Uq... 

Exploiting the properties of aqueous surfactant solutions in which the surfactants aggregate to form micelles consisting of apolar cores comprised of the hydrophobic tail groups stabilized by coronae formed by the hydrophilic surfactant heads (Fendler and Fendler, 1975 Bunton, 1991). The apolar core plays the role of the organic solvent, whereas the palisade layer can provide a medium of intermediate polarity. 

---