Temperature effects microemulsions

Minimizing the temperature effects discussed above could be obtained with the use of polymer micelles or polymer surfactants [81-83], whose CMC is zero, and even in nonaqueous solvent, the micelle is stable. Although several polymer surfactants are commercially available, no such surfactant is widely accepted, probably because SDS, CTAB, or CTAC, and bile salts are superior to polymer surfactants as the pseudostationary phase in MEKC. Although microemulsion electrokinetic chromatography (MEEKC) is not discussed in this chapter but covered in Chapter 4 by Altria and colleagues, a similar optimization strategy to that in MEKC applies to MEEKC [84-86]. Since... 

Rozman B, Zvonar A, Faison F, and Gasperlin M. (2009). Temperature-sensitive microemulsion gel An effective topical delivery system for simultaneous delivery of vitamins C and E. AAPS PharmSciTech, 10, 54-61. 

It is evident from the DLS measurements that the microemulsions are monodis-perse and the size of aggregates in all the microemulsions decreases with increasing temperature. This indicates the noninteracting hard sphere nature of the aggregates in RTILs/[C mim][AOT]/benzene microemulsions at R = 1.0 without droplet coalescing [62, 92, 96]. The microemulsions retain their structural integrity aeross the temperature range used in the study. The temperature effect on the... 

Saidi, Z., Boned, C., and Peyrelasse, J., Viscosity-percolation behavior of waterless Microemulsions a curious temperature effect, In Trends in Colloid and Interface Science VI (C. Hehn, M. Losche, H. Mohwaldt, Eds.) Springer, The Netherlands, 1992, pp. 301-316. 

This provides for interesting applications because, in contrast to fatty alcohol ethoxylates, temperature-stable microemulsions can be formed with alkyl polyglycosides. By varying the surfactant content, the type of surfactant used, and the oil/water ratio, microemulsions can be produced with custom-made performance properties, such as transparency, viscosity, refatting effect, and foaming behavior. In mixed systems of, say, alkyl ether sulfates and nonionic coemulsifiers (alkyl polyglycoside), extended microemulsion areas... 

FIG. 27 Temperature effect on the microemulsion phase of a system of decylglucoside (APG), glycerol monooleate (GMO), lauryltetraglycolether (laureth-4), dioctyl cyclohexane, and water at a water concentration of 90 % weight [79]. 

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 addition of linear chained alkyl alcohols shifts the percolation of AOT microemulsions to higher temperature, whereas the opposite effect is obtained by adding polyoxyethylene alkyl ethers [261]. 

Another example of chemical-potential-driven percolation is in the recent report on the use of simple poly(oxyethylene)alkyl ethers, C, ), as cosurfactants in reverse water, alkane, and AOT microemulsions [27]. While studying temperature-driven percolation, Nazario et al. also examined the effects of added C, ) as cosurfactants, and found that these cosurfactants decreased the temperature threshold for percolation. Based on these collective observations one can conclude that linear alcohols as cosurfactants tend to stiffen the surfactant interface, and that amides and poly(oxyethylene) alkyl ethers as cosurfactants tend to make this interface more flexible and enhance clustering, leading to more facile percolation. 

---