Surfactants emulsion formation

One of the main problems associated with developing a parenteral or any other solution formulation of a compound is its aqueous solubility. For poorly soluble drug candidates, there are several strategies for enhancing their solubility. These include pH manipulation, cosolvents, surfactants, emulsion formation and complexing agents. More sophisticated delivery systems, e.g., liposomes, can also be used in this way. 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

In-situ emulsion formation, as proposed by Kamath et al(19), with DAS surfactants may cause higher pressure drops across the core. This is because of the blocking tendency of the emulsion which has lower mobility. This could explain the earlier plugging of the core compared to other runs. Effluent pH and viscosity showed behavior similar to the previous runs. It is worthwhile noting here that such pressure drops were not manifested by face plugging of the core near the entrance. This was confirmed by simultaneously monitoring the pressure at the inlet end of the core as well as the differential pressure across the two pressure taps located about 1 cm. from each end of the core. The inlet end pressure transducer showed reasonably low pressures throughout the run for each experiment. 

Izquierdo, P., Feng, J., Esquena, J.,Tadros, T.F., Dederen, J.C., Garcia, M.J., Azemar, N. and Solans, C. (2005) The influence of surfactant mixing ratio on nano-emulsion formation by the PIT method. Journal of Colloid and Interface Science, 285 (1), 388-394. 

However, oil and water can be dispersed with the help of suitable emulsifiers (surfactants) to give emulsions (Sjoblom et al., 2008 Birdi, 2008). This is a well-known fact with emulsions found in the home, such as mayonnaise, the basic reason being that the interfacial tension (IFT) between oil and water is around 50 mN/m, which is high, and which leads to the formation of large oil drops. On the other hand, the addition of suitable emulsifiers reduces IFT to very low values (even much less than 1 mN/m). Emulsion formation means that oil drops remain dispersed for a given length of time (even up to many years). The stability and the characteristics of these emulsions are related to the areas of their applications. 

One advantage of using a cleavable acetal surfactant instead of a conventional amphiphile has been elegantly demonstrated in a work by Bieniecki and WUk [51]. A cationic 1,3-dioxolane derivative was used as surfactant in a microemulsion formulation that was employed as a reaction medium for an organic synthesis. When the reaction was complete, the surfactant was decomposed by addition of acid and the reaction product easily recovered from the resulting two phase system. Through this procedure the problems of foaming and emulsion formation, frequently encountered with conventional surfactants, could be avoided. 

This brief review has attempted to discuss some of the important phenomena in which surfactant mixtures can be involved. Mechanistic aspects of surfactant interactions and some mathematical models to describe the processes have been outlined. The application of these principles to practical problems has been considered. For example, enhancement of solubilization or surface tension depression using mixtures has been discussed. However, in many cases, the various processes in which surfactants interact generally cannot be considered by themselves, because they occur simultaneously. The surfactant technologist can use this to advantage to accomplish certain objectives. For example, the enhancement of mixed micelle formation can lead to a reduced tendency for surfactant precipitation, reduced adsorption, and a reduced tendency for coacervate formation. The solution to a particular practical problem involving surfactants is rarely obvious because often the surfactants are involved in multiple steps in a process and optimization of a number of simultaneous properties may be involved. An example of this is detergency, where adsorption, solubilization, foaming, emulsion formation, and other phenomena are all important. In enhanced oil recovery. 

There are a number o-f processes which have not been discussed (because o-f space) in which mixture o-f sur-f actants are important. Among these are foaming, emulsion formation, liquid crystal formation, microemulsion formation, adsorption as 1iquid—1iquid interfaces, and phase partitioning of surfactants between immiscible liquid phases. These areas will also see increased interest in the use of surfactant mixtures. 

Heat can be used to break some emulsions Changing the pH of the water can often break an emulsion The presence of acid-forming and sulfate-reducing microorganisms may enhance the formation of emulsions treat the fuel with a microbiocide Formulate fuels with a demulsifier to inhibit emulsion formation Ensure that surfactant compounds and additives... 

Dynamic processes are prominent among potential applications of lyotropic liquid crystals. It is known, for example, that emulsion stability is greatly enhanced when liquid crystal forms at the surfaces of the drops (4). However, emulsion formation is invariably a dynamic process, involving fluid flow and transport of the surfactant from one liquid to the drop surfaces and the other liquid. Since the time required to reach equilibrium in systems containing liquid crystals can sometimes be quite long—weeks or months—the need for knowledge about dynamics of the process is evident. 

The interfacial tension is a key property for describing the formation of emulsions and microemulsions (Aveyard et al., 1990), including those in supercritical fluids (da Rocha et al., 1999), as shown in Figure 8.3, where the v-axis represents a variety of formulation variables. A minimum in y is observed at the phase inversion point where the system is balanced with respect to the partitioning of the surfactant between the phases. Here, a middle-phase emulsion is present in equilibrium with excess C02-rich (top) and aqueous-rich (bottom) phases. Upon changing any of the formulation variables away from this point—for example, the hydrophilie/C02-philic balance (HCB) in the surfactant structure—the surfactant will migrate toward one of the phases. This phase usually becomes the external phase, according to the Bancroft rule. For example, a surfactant with a low HCB, such as PFPE COO NH4+ (2500 g/mol), favors the upper C02 phase and forms w/c microemulsions with an excess water phase. Likewise, a shift in formulation variable to the left would drive the surfactant toward water to form a c/w emulsion. Studies of y versus HCB for block copolymers of propylene oxide, and ethylene oxide, and polydimethylsiloxane (PDMS) and ethylene oxide, have been used to understand microemulsion and emulsion formation, curvature, and stability (da Rocha et al., 1999). 

Sometimes the surfactants used for cleaning in manufacturing processes create undesirable O/W emulsions. This can be difficult to deal with since emulsification is usually an important aspect of a cleaning process. If the process or the detergent formulation cannot be adjusted to prevent the undesirable emulsion formation then a separate demulsification/separation step may be needed. In some cases these emulsions can be broken by separating out and concentrating the dispersed phase, such as by membrane ultrafiltration [454],... 

Forster. T. Principles of Emulsion Formation in Surfactants in Cosmetics, Rieger, M.M. Rhein, L.D. (Eds.), Marcel Dekker New York,... 

Additives are usually amphiphilic in nature, and thus are either ionic or neutral surfactants or even polymers. The role of surfactants in solvent extraction is ambiguous. Usually, they should be avoided as they lower the interfacial tension, which may lead to emulsion formation in an agitated extractor. However, every metal-loaded ion exchanger is amphiphilic, and can adsorb at the interface or aggregate in the bulk phase. This occurrence is well known with sodium or other metals [17], and above a critical surfactant concentration (cmc, critical micelle concentration) micellar aggregates are formed. A dimensionless geometric parameter is decisive for the structure of the associates, according to Fig. 10.6 ... 

The most significant problem with the utilization of surfactant media in different separation schemes (particularly those at the preparative or process scales) concerns the recovery of the analyte from the surfactant media and subsequent recovery of the surfactant for re-use. Attempts to use extraction schemes with conventional organic solvents typically results in troublesome emulsion formation during the recovery steps. There are, however, several means available by which analytes can be recovered free of surfactant. These include the following (1) Several quick, gentle methods for the recovery of some analytes (usually proteins) from surfactant media (i.e. micellar NaLS, Triton X-100, CHAPS, deoxycholate, Brij-35) via use of column chromatography have been developed (509-515). Most of the stationary phase materials for this approach are available commercially (510,513). 

A similar study was performed on the formation of nano crystalline HA in nonionic surfactant emulsions [163]. Instead of using NP-5/NP-9 surfactant, KB6ZA (nonionic surfactant which is a lauryl alcohol condensed with an average of 6 mol of oxyethylene oxide) was used together with petroleum ether as the oil phase to prepare HA powder in an 0/W emulsion system. One of the very apparent advantages of using 0/W emulsion over W/0 microemulsion is... 

Many surfactants have been suggested as candidates for CO2 foam. However, at high salinity and temperature in the presence of oil, most surfactants foam poorly due to partitioning and emulsion formation and fail to control mobility during CO2 injection. This behavior is analogous to that observed in chemical (microemulsion) oil recovery (5-1). As the salinity, hardness and temperature increase, surfactants form water/oil emulsions, precipitate surfactant-rich coacervate phases, and partition into the oleic phase. CO2 decreases further the solubility of surfactant in the aqueous phase. 

To be a promising candidate for CO2 foam, the surfactant loss by adsorption, partitioning and emulsion formation must be low. In general, anionic surfactants have low adsorption on sandstones and high adsorption on carbonates, whereas the reverse is true for nonionics ( ). Cationic surfactants are not considered because of their high adsorption on many surfaces. 

Emulsion Formation. Oil-in-water emulsions can be produced by agitating oil with an aqueous solution of emulsifier (agent-in-water method) or by utilizing the naturally occurring surfactants already present in some oils (agent-in-oil method). Either method is suitable for creation of the emulsion above ground and injection of that emulsion into the reservoir. 

Certain compounds, because of their chemical structure, have a tendency to accumulate at the boundary between two phases. Such compounds are termed amphiphiles, surface-active agents, or surfactants. The adsorption at the various interfaces between solids, liquids and gases results in changes in the nature of the interface which are of considerable importance in pharmacy. For example, the lowering of the interfacial tension between oil and water phases facilitates emulsion formation the adsorption of surfactants on the insoluble particles enables these particles to be dispersed in the form of a suspension and the incorporation of insoluble compounds within micelles of the surfactant can lead to the production of clear solutions. 

The droplet deformation increases with increases in the Weber number which means that, in order to produce small droplets, high stresses (i.e., high shear rates) are require. In other words, the production of nanoemulsions costs more energy than does the production of macroemulsions [4]. The role of surfactants in emulsion formation has been described in detail in Chapter 10, and the same principles apply to the formation of nanoemulsions. Thus, it is important to consider the effects of surfactants on the interfacial tension, interfacial elasticity, and interfacial tension gradients. 

Another consequence of the addition of fatty alcohols to cationic surfactants is the formation, under the right conditions, of liquid crystal and gel networks [41-45] that can greatly increase viscosity and confer stability upon the emulsion. Formation of such liquid crystals has been observed even at low concentrations [44,45] the ready formation of these structures, along with low cost, improved stability, and compatibility with cosmetic ingredients are important reasons why long-chain alcohols are so ubiquitous in conditioning formulations. 

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