Surfactants water-in-oil

Figure 11. Size- and shape-control of nanoparticles via salt reduction in (a) the hydrophobic core of a surfactant oil in water micelle and (b) the hydrophilic core of a water-in-oil reverse micelle.

Figure 8 Intraparticle preparation of colloidal metals in (a) surfactant oil in water micelles or (b) water-in-oil reverse micelles as microreactors. (Reproduced after [2b], Figs. 6-10, p. 481.)...

Figure 6-10. a) Surfactant oil in water micelles, b) water-in-oil reverse mieelles, and c) vesicles. Metal colloids can be generated in the intraparticle space. 

Emulsions. Aerosol emulsions (qv) may be oil in water (o/w), such as shaving creams, or water in oil (w/o), such as air fresheners and pohshes. These aerosols consist of active ingredients, an aqueous or nonaqueous vehicle, a surfactant, and a propellant, and can be emitted as a foam or as a spray. 

An a priori method for choosing a surfactant was attempted by several researchers (50) using the hydroph i1 e—1 ip oph i1 e balance or HLB system (51). In the HLB system a surfactant soluble in oil has a value of 1 and a surfactant soluble in water has a value of 20. Optimum HLB values have been reported for latices made from styrene, vinyl acetate, methyl methacrylate, ethyl acrylate, acrylonitrile, and their copolymers and range from 11 to 18. The HLB system has been criticized as being imprecise (52). 

Surfactants. Surfactants (qv) perform a variety of functions in a drilling fluid. Depending on the type of fluid, a surfactant may be added to emulsify oil in water (o/w) or water in a nonaqueous Hquid (w/o), to water-wet mud soHds or to maintain the soHds in a nonwater-wet state, to defoam muds, or to act as a foaming agent. 

Body washes are another more recent introduction into the marketplace. These products have become a mainstay in the European market and, in only a few years, have grown to be a significant fraction of the U.S. market. Body washes can be simple formulas similar to those used for Hquid handsoaps or complex 2-in-l oil-in-water emulsion, moisturizing formulations. These products contain a wide range of synthetic surfactants not typically found in bar... 

The pelobischofite-surfactant mixtures emulsifying ability was estimated by measurements of the phase immiscibility time for standard oil in water emulsion. The measurements of emulsion particles size were also carried out. The experiments showed the essential increase of phase immiscibility time with the pelobischofite contents increase. Some decrease in average particles size of standard emulsion was also registered. The emulsifiability of other magnesium containing preparations was at least twice worse. 

These characteristics are typically classified as a hydrophile-lipophile balance (HLB value). For example, hydrophilicity may be denoted within a range of 2 to 20, with true solutions being obtained at HLB values >14 and poor dispersibility occurring at HLB values <6. Oil-in-water emulsification requires a high HLB value surfactant, while water-in-oil emulsification needs a low HLB value surfactant. 

The ingredients are nonionic surfactants. It is their application as amine replacements in steam-condensate systems that is novel, not the raw materials. These products are commonly found in skin and hair products and in cosmetics because of their mildness and their excellence as water-in-oil emulsifiers and co-emulsifiers in oil-in-water emulsions. Raw material brands include Tween (ICI, PLC), Crill , and Crillet (Croda PLC). 

Besides the alkyl ether carboxylates the amidether carboxylates are used as mild surfactants in cosmetic formulations [35-37,68,69,71,80]. As described by Meijer [68,69], the ether carboxylate mixture derived from the monoethanol-amide of coconut oil is a mild product in shampoos and showerbaths, and the stearylmonoethanolamidether carboxylate an oil-in-water emulsifier for creams and lotions. The NDELA content of these products is below the detection level of 10 ppb because of the use of monoethanolamine and the further chemical reactions after amidation. 

In a multiphase formulation, such as an oil-in-water emulsion, preservative molecules will distribute themselves in an unstable equilibrium between the bulk aqueous phase and (i) the oil phase by partition, (ii) the surfactant micelles by solubilization, (iii) polymeric suspending agents and other solutes by competitive displacement of water of solvation, (iv) particulate and container surfaces by adsorption and, (v) any microorganisms present. Generally, the overall preservative efficiency can be related to the small proportion of preservative molecules remaining unbound in the bulk aqueous phase, although as this becomes depleted some slow re-equilibration between the components can be anticipated. The loss of neutral molecules into oil and micellar phases may be favoured over ionized species, although considerable variation in distribution is found between different systems. 

The rates of multiphase reactions are often controlled by mass tran.sfer across the interface. An enlargement of the interfacial surface area can then speed up reactions and also affect selectivity. Formation of micelles (these are aggregates of surfactants, typically 400-800 nm in size, which can solubilize large quantities of hydrophobic substance) can lead to an enormous increase of the interfacial area, even at low concentrations. A qualitatively similar effect can be reached if microemulsions or hydrotropes are created. Microemulsions are colloidal dispersions that consist of monodisperse droplets of water-in-oil or oil-in-water, which are thermodynamically stable. Typically, droplets are 10 to 100 pm in diameter. Hydrotropes are substances like toluene/xylene/cumene sulphonic acids or their Na/K salts, glycol.s, urea, etc. These. substances are highly soluble in water and enormously increase the solubility of sparingly. soluble solutes. 

Oil-in-water emulsions provide a cost-effective alternative to the methods mentioned previously, namely, heating or diluting. A typical transport emulsion is composed of 70% crude oil, 30% aqueous phase, and 500 to 2000 ppm of a stabilizing surfactant formulation [1497]. Nonionic surfactants are relatively insensitive to the salt content of the aqueous phase ethoxylated alkylphenols have been used successfully for the formation of stable emulsions that resist inversion. 

Water-in-oil macroemulsions have been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, the use of water-in-oil and oil-in-water macroemulsions have been evaluated as drive fluids to improve oil recovery of viscous oils. Such emulsions have been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. In this study, the emulsions were stabilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil emulsion. It is well known, therefore, that the stability of such emulsions substantially depends on the use of sodium hydroxide (i.e., caustic) for producing a soap film to reduce the oil/water interfacial tension. 

Modem oil spill-dispersant formulations are concentrated blends of surface-active agents (surfactants) in a solvent carrier system. Surfactants are effective for lowering the interfacial tension of the oil slick and promoting and stabilizing oil-in-water dispersions. The solvent system has two key functions (1) to reduce the viscosity of the surfactant blend to allow efficient dispersant application and (2) to promote mixing and diffusion of the surfactant blend into the oil film [601]. 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

The anhydrous petrolatum base may be made more miscible with water through the use of an anhydrous liquid lanolin derivative. Drugs can be incorporated into such a base in aqueous solution if desired. Poly-oxyl 40 stearate and polyethylene glycol 300 are used in an anti-infective ointment to solubilize the active principle in the base so that the ointment can be sterilized by aseptic filtration. The cosmetic-type bases, such as the oil-in-water (o/w) emulsion bases popular in dermatology, should not be used in the eye, nor should liquid emulsions, owing to the ocular irritation produced by the soaps and surfactants used to form the emulsion. 

Phase Inversion The phase inversion of brine/oil/surfactant systems was established routinely by measuring solution conductivity employing a Jenway FWA 1 meter and cell. The process identifies the range over which a large decrease in conductivity occurs as the sytem under test is converted from an oil in water emulsion to a water in oil emulsion. Phase... 

Surfactant molecules can be considered as building blocks for certain forms of geometry in colloidal chemistry. Various forms of association molecules can be obtained as the concentration of surfactant in water is increased and/or physicochemical conditions are changed (e.g. CMC, Craft-point, etc.). Figure 2 schematically shows the most likely structural configurations and assemblages of surfactants association in an aqueous system (26). Upon addition of oil and a short-chain alcohol, for example, one can convert the oil-in-water micelles into water-in-oil microemulsions. It is therefore possible to induce a transition from one structure to another by changing the physicochemical conditions such as temperature, pH and addition of mono or di-valent cations to the surfactant solution. It should be also noted that the sur-... 

Continuous aqueous phase emulsion polymerization is one of the most widely used procedures to make nanoparticles for drug delivery purposes, especially those prepared from the alkylcyanoacrylate monomers. An oil-in-water emulsion system is employed where the monomer is emulsified in a continuous aqueous phase containing soluble initiator and surfactant [39, 40]. Under these conditions, the monomer is partly solubilized in micelles (5-10 nm), emulsified as large... 

The most widely studied deformable systems are emulsions. These can come in many forms, with oil in water (O/W) and water in oil (W/O) the most commonly encountered. However, there are multiple emulsions where oil or water droplets become trapped inside another drop such that they are W/O/W or O/W/O. Silicone oils can become incompatible at certain molecular weights and with different chemical substitutions and this can lead to oil in oil emulsions O/O. At high concentrations, typical of some pharmaceutical creams, cosmetics and foodstuffs the droplets are in contact and deform. Volume fractions in excess of 0.90 can be achieved. The drops are separated by thin surfactant films. Selfbodied systems are multicomponent systems in which the dispersion is a mixture of droplets and precipitated organic species such as a long chain alcohol. The solids can form part of the stabilising layer - these are called Pickering emulsions. 

Similar investigations have been carried out on water in oil microemulsions. A microemulsion is a clear, transparent, and stable system consisting of essentially monodisperse oil in water (OAV) or water in oU (W/O) droplets with diameters generally in the range of 10-200 nm. Microemulsions are transparent because of their small particle size, they are spherical aggregates of oil or water dispersed in the other liquid, and they are stabilized by an interfacial film of one or more surfactants. 

The influence of surfactant structure on the nature of the microemulsion formed can also be predicted from the thermodynamic theory by Overbeek (17,18). According to this theory, the most stable microemulsion would be that in which the phase with the smaller volume fraction forms the droplets, since the osmotic term increases with increasing i. For w/o microemulsion prepared using an ionic surfactant, the hard sphere volume is only slightly larger than the water volume, since the hydrocarbon tails of the surfactant may interpenetrate to a certain extent, when two droplets come close together. For an oil in water microemulsion, on the other hand, the double layer may extend to a considerable extent, depending on the electrolyte concentration... 

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