Solubilization ternary systems

Addition of poly(styrene-block-butadiene) block copolymer to the polystyrene-polybutadiene-styrene ternary system first showed a characteristic decrease in interfacial tension followed by a leveling off. The leveling off is indicative of saturation of the interface by the solubilizing agent. 

The effect of adding a surfactant, (NaDDS), was also investigated. One such case only is shown in Fig. 6 where BE is replaced by a 5 1 mixture of BE-NaDDS. The main effect of NaDDS is to increase the miscibility range of the oil in water. Various ratios of BE-NaDDS were used and, as a first approximation, the change in the phase diagram is directly proportional to the concentration of NaDDS. The addition of a surfactant probably stabilizes the microstructures which were already present in the ternary system BE-DEC-H O and decreases the quantity of BE needed to solubilize DEC. Therefore the presence of a surfactant is useful but not essential to the stability of microemulsions. 

Bourrel M, Chambu C (1983) The Rules for Achieving High Solubilization of Brine and OU by AmphiphUic Molecules. Soc Petrol Eng J 23 327-338 Kunieda H, Shinoda K (1985) Evaluation of the hydrophile-lipophile balance (HLB) of nonionic surfactants I. Multisurfactant systems. J Colloid Interface Sci 107 107-121 Kahlweit M, Strey R, Eirman P (1986) Search for tricritical points in ternary systems Water-oil-nonionic amphiphile. J Phys Chem 90 671... 

It is sometimes argued that the reverse micelle terminology is an inappropriate comparison to aqueous micelles. Since water can be solubilized by these micelles, causing an increase in n, the reverse micelle model and vocabulary do seem useful for ternary systems. 

Rubino et al. [64-66] studied solubilization by cosolvents in binary and ternary systems. They determined that the solubility of poor water-soluble drugs was approximately described by the log-linear solubility equation as applied to multiple solvent systems ... 

CMC determinations as a function of temperature utilizing the change of the amount of solubilized water are inaccurate. This procedure has been frequently applied. In this way, for example, the effect of the temperature on the CMC of hexa-oxyethylene dodecylether in cyclohexane183) was determined. The CMC loses its well defined meaning in a ternary system, viz. to represent a thermodynamic property of the particular surfactant/solvent system (see Paragraph 2.2). 

Standard Nd-based catalysts comprise binary and ternary systems. Binary systems consist of Nd chloride and an aluminum alkyl or a magnesium alkyl compound. In ternary catalyst systems a halide free Nd-precursor such as a Nd-carboxylate is combined with an Al- or Mg-alkyl plus a halide donor. By the addition of halide donors to halide-free catalyst systems catalyst activities and cis- 1,4-contents are significantly increased. In quaternary catalyst systems a solubilizing agent for either the Nd-salt or for the halide donor is used in addition to the components used in ternary systems. There are even more complex catalyst systems which are described in the patent literature. These systems comprise up to eight different catalyst components. 

Solubilization can be defined as the preparation of a thermodynamically stable isotropic solution of a substance normally insoluble or very slightly soluble in a given solvent by the introduction of an additional amphiphilic component or components. The amphiphilic components (surfactants) must be introduced at a concentration at or above their critical micelle concentrations. Simple micellar systems (and reverse micellar) as well as liquid crystalline phases and vesicles referred to above are all capable of solubilization. In liquid crystalline phases and vesicles, a ternary system is formed on incorporation of the solubilizate and thus these anisotropic systems are not strictly in accordance with the definition given above. 

Solubilization, Microemulsions and Emulsions. - Micellar solutions with both normal (Li) and reverse (L2) curvature, e.g. o/w and w/o type systems, can be swollen by oil and water to obtain water/oil/amphiphile ternary or pseudoternary systems. These systems have been widely used as solubilizing media for structural investigations of the immobilized solubilizate (a protein for instance), for drug delivery systems, and also for reaction media, (micellar catalysis). Ternary systems based on water, oil, and amphiphile mixtures can form a variety of Li and L2 monophasic regions. When these systems form isotropic solutions spontaneously, they are termed microemulsions. The formation of a microemulsion is related mainly to a substantial decrease of the interfacial tension (Yo/w) at the oil-water interface, due to the amphiphilic molecules located at the polar-apolar interface. This occurs in agreement with the typical equation ... 

Specific roles of the so-called co-surfactants (commonly, but not necessarily alcohols) have been examined by various workers [122, 126, 136] some points are discussed here. For example, a critical thermodynamic analysis in conjunction with experimentations led Eicke [ 136] to the conclusion that a co-surfactant should decrease the interfacial free energy under isothermal conditions, while causing an uptake of water into the microemulsion and extension of its domain. The anionic surfactant AOT assists the formation of large reverse microemulsion domains (high water uptake) in different ternary systems without help from a co-surfactant (Section 2.2), but cationic surfactants do generally need this fourth component. In spite of this, enhanced solubilization by the addition of (small quantities of) a co-surfactant has been observed by various workers in AOT systems. Eicke [136] used cyclohexane, benzene, carbon tetrachloride and nitrobenzene in the system AOT/ isooctane/water and found considerable water uptake (the fraction of the oil phase, i.e. isooctane was 0.8 or more). With increasing polarizability or polarity of the CO-surfactant, the water uptake decreased. 

In ord to optimize the applications of SSI technique different problems should be solved with the help of experimental determinations coupled widi some theoretical analysis. It is obvious that the polymer in contact with the supercritical fluid swells (the CO2 dissolves in the polymer) and the extent of swelling depends from the pressure. When the polymer is in contact with the supercritical fluid saturated with the pharmaceutical the solvent again diffuses in the polymer, it swells the polymer and in this way the solubilization of the drug in the polymer is fricilitated. As a consequence in addition to the kinetic problems (diffusion in the polymer matrix) the thermodynamic description of the ternary systems, supa critical fluid, pharmaceutical and polymer, is essential. 

A typical phase diagram of a ternary system of water, ionic surfactant and long-chain alcohol (co-surfactant) is shown in Figure 15.5. The aqueous micellar solution A solubilizes some alcohol (spherical normal micelles), whereas the alcohol solution dissolves huge amounts of water, forming inverse micelles, B. These two phases are not in equilibrium, but are separated by a third region, namely the lamellar liquid crystalline phase. These lamellar structures and their equilibrium with the aqueous micellar solution (A) and the inverse micellar solution (B) are the essential elements for both microemulsion and emulsion stability [3]. 

A common problem in the evaluation of binary and ternary systems to which a solute has been added is the basic distinction between the mean area per molecule and the partial molecular surface. When areas per molecules are measured, the link between total area and molar fraction may be highly nonlinear, in particular for the case of solutes denominated as cosurfactants which are solubilized in the palisade layer. The partial molar area is the increase of surface per surfactant due to the addition of a solute at a constant density of surfactant, while the area is the observed average. This problem has been discussed in detail by Boden et al. (5). 

In this section, we will focus on the solubilization of a substance in water-oil-surfactant samples containing initially three components. These ternary systems include microemulsions (w/o, o/w and bicontinous), lamellar phases and other liquid crystal mesophases. On a microscopic scale, oil microdomains are separated from water microdomains by a surfactant interface. A microdomain is here understood to be an aggregate of at least the order of a hundred self-assembled molecules, although being too small to be considered as a microphase-separated sample. A sample contains separated microphases when domains of micron size of two thermodynamically stable different phases co-exist and do not de-mix even after centrifugation, due to kinetic stability. The solute can then be located at the interface or in the oil or water microdomain (cf. Figure 9.9). Since three environments are available in ternary systems, the interface can be considered as a pseudo-phase or as a surfactant monolayer (37). 

Many surfactant solutions are known which contain spherical micelles up to high surfactant concentrations and behave as Newtonian liquids with a low viscosity. This is especially the case for ternary systems of surfactant, hydrocarbon and water where the spheres are stabilized by the solubilization of the non-polar hydrocarbon. 

Ternary systems are encountered in pharmacy mainly as emulsifier-oil-water systems in emulsions or as surfactant-solubilizate-water systems in the formulation of solubilized systems. Phase equilibria within ternary systems are most conveniently represented by a triangular phase diagram which delineates the phase regions enabling the formulator to select suitable combinations of the three components to produce stable emulsions or clear isotropic solubilized systems. 

As discussed in Chapter 2, liquid crystalline regions such as the neat and middle phases formed in concentrated surfactant solutions are capable of incorporation of solubilizates. The ternary systems so formed represent a type of solubilized system although such systems, being anisotropic, are not strictly in accordance with the definition of a solubilized system proposed above. Relatively few studies of these systems have been reported and we shall in this chapter concentrate exclusively on solubilization within the micellar, L, and the reverse micellar, L2, isotropic regions. 

Lawrence [10-12] extended this work, suggesting that the increased solubility of a solubilizate in a surfactant solution was due to some form of attachment of the solubilizate to the exterior of the micelle or solution in it. He also pointed out a difference in behaviour when polar and non-polar molecules were solubilized, and the increased solubility of the soap itself with the addition of a polar solubilizate. Hartley [13] made the further contribution that solubilization occurred only above the CMC above this, the amount of substance solubilized increased with soap concentration. This work in turn evolved a widely used technique for determining the CMC, but great care must be taken in evaluating results from this technique, as it involves the use of ternary systems to investigate a binary one. 

Other aspects of formulation such as the nature of the binary or ternary vehicle (oil-surfactant, water-surfactant or oil-water-surfactant, respectively) have been considered recently [151], Addition of polysorbate 80 to the aqueous phase has no significant effect on the epidermal transport of ethanol, but a significant reduction in the transport of the less soluble octanol results, in line with the arguments presented above in isopropyl myristate, octanol transport is not affected by the solubilizer while that of ethanol is decreased. In the ternary systems identified in Fig. 7.35, the results in Table 7.14 were obtained indicating a general decrease in permeability constants for ethanol, butanol and octanol. The viscosity of the vehicles was not a factor although this varied from 1 to 39 X 10 cP. In the ternary systems a surfactant will distribute itself between the aqueous and non-aqueous phase quantitative prediction of permeation is made difficult even with data on the transport properties of the permeants in the individual phase. The results indicate that the percutaneous absorption of the... 

---