Microemulsion components

The microemulsion components, particularly the nature of the oil, has been shown to have a dramatic effect on the interaction of metal ions in the microdroplet Interfaclal region. In particular, the change from benzene to mineral oil causes a change in the quinoline dependence of the rate of metalloporphyrin formation and a 0.9 volt shift in copper(II) half- ave potential. The... 

Using the above principle, Lindman and coworkers [16-18] measured the selfdiffusion coeflBdents of all microemulsion components, with particular emphasis on the role of the cosurfactant. For microemulsions consisting of water, hydrocarbon, an anionic surfactant and a short-chain alcohol (C4 and C5), the setf-diffusion coefficient of water, hydrocarbon and cosurfactant was quite high (on the order of 10 s ), which was two orders of magnitude higher than the value expected... 

Lehmann et al. have demonstrated the in vivo potential of hydrocortisone-loaded microemulsions in comparison to the marketed product by comparing the blanching effect in humans produced by the various formulations [69]. It was observed that the o/w mi-croemulsion had significantly greater blanching effect than the w/o microemulsion and marketed cream. However, it also resulted in the significant skin irritation in the subjects as compared to the other formulations. This clearly shows the need to evaluate the effect of the microemulsions in terms of tolerability. However, it is noteworthy that the tolerability is mainly governed by the nature of the microemulsion components and by the careful selection of the components, this limitation can be overcome. 

As described earlier, poor permeability is also one of the major factors that limit oral bio availability of several drugs like atenolol and acyclovir because of which such drugs have to be administered at significantly higher doses than required. Several microemulsion components, for example, oil phases such as oleic acid, mono glycerides of caprylic acid... 

If large quantities are used for technical processes, e.g. for cleaning, the recovery and reuse of the microemulsion or at least of a considerable amount of the most expensive components is desired. Therefore, strategies are needed to separate contaminants from the organic microemulsion components. Separation is usually more complicated than from ordinary solvents and often requires several steps [39, 40]. In particular, the separation of waste materials from the surfactants is usually very difficult or often even impossible. The temperature-dependent phase behaviour of bicontinuous microemulsions, however, can sometimes be beneficially used for separation [41]. Easy separation, at least from the unpolar solvent, can be achieved from microemulsions with supercritical liquids [42]. 

As there are other less sophisticated and less expensive techniques available, surfactant-enhanced aquifer remediation will only be useful for decontamination of LNAPL sites in special cases. However, applicable techniques are still needed for DNAPL sites and microemulsion techniques are really promising. Therefore, most research has concentrated on this type of contaminant in recent years. Integrated concepts have been developed including aspects of soil properties [47, 48, 62, 63], density control [47, 48, 62-64], recovery and reuse of microemulsion components [47], biological degradation of residues of contaminants and injected compounds [48, 65] and costs [47, 48, 64, 65]. Two main approaches have been followed for developing effective surfactant systems which form microemulsions with DNAPL, but do not mobilise the liquid contaminant into deeper... 

Surfactant-enhanced aquifer remediation is relatively expensive. Thus, waste reduction or the reuse of at least a considerable part of the microemulsion components is interesting. 

Microemulsion-based gel showed greater retention of drug into skin layers than microemulsion and market preparation. Microemulsion-based gel was found to be significantly less irritating. Results indicated interaction of microemulsion components with skin, resulting in permeation enhancement and retention of drug into skin layers. 

Patel MR, Patel RB, Parikh JR, Solanki AB, and Patel BG. (2011). Investigating effect of microemulsion components In vitro permeation of ketoconazole. Pharmaceutical Development and Technology, 16, 250-258. 

The electrochemical oxidation of ferrocene and amphiphilic ferrocenes, 2- and 5-(ferrocenylcarboxy)dodecyltrimethylammonium nitrates (2-Fc and 5-Fc, respectively), were investigated in a bicontinuous microemulsion containing CTAC, -tetradecane, pentanol, and water [83]. The electron transfer rates for ferrocene, 2-Fc, and 5-Fc in microemulsions were an order of magnitude slower than in acetonitrile, possibly due to partial inhibition by microemulsion components adsorbed on the electrode [5,6]. The rates of electron transfer of 2-Fc and 5-Fc were only two-fold smaller than that of ferrocene, in contrast to 10-fold (2-Fc) and 100-fold (5-Fc) smaller in CTAB micelles [84]. These results indicate an increased disorder and mobility at the electrode/fluid interface in the CTAC microemulsion compared to CTAB micellar system [83]. 

In this chapter we surveyed the use of SZT-DSC in recent investigations of microemulsions. Two factors combine to militate against the more frequent use of this technique in microemulsion research. First, a great deal of careful work is required to obtain insight into the nature of interactions between microemulsion components and, especially, into the role of water in such interactions. Second,... 

An interesting application of ionic liquids (ILs) concerns their use in combination with classical surfactants [1,2]. Indeed, they can suitably replace each of the microemulsion components (aqueous phase, apolar phase, and surfactants) conferring peculiar features to self-assembled systems. Indeed, ILs are salts and as such have affinity for water, but they also typically possess a lipophilic moiety, and this means affinity for oils. Depending on their chemical structure, ILs can act as cosolvent either for water or for oil. In addition, when their hydrophilic and hydrophobic nature are both strong enough, a fraction of ILs will reside preferentially at the interface formed by the surfactant, and this can impact dramatically the interfacial physics, drastically changing the microemulsion structure and dynamics. 

The surface activity of ibuprofen is raising the possibility that on solubilization in microemulsions it wiU not only remain in oil phase but also be incorporated in surfactant film where it may act as a cosurfactant and consequently interact with other microemulsion components that could affect the release. 

The results are in agreement with the recent release study of nonsteroidal drug ketoprofen [6]. Despite the fact that the ketoprofen release was studied by different techniques and therefore the release rate values are not comparable directly, the same tendency was observed. Additionally, it has been shown [34] that incorporation of ketoprofen does not alter the microemulsion system significantly however, its presence prevents the formation of stronger interaction and formation of gel-like structure in water rich region. It was also found out that stronger interactions between microemulsion components in W/O as well in the bicontinuous phase lead to slower ketoprofen release. Because of similar molecule structure of ibuprofen the same could be assumed also for it. We can conclude that release behavior of ibuprofen is influenced with the microstructure and can be predicted to a certain extent, using a combination of several tested methods for physical characterization of microemulsions. 

The same authors used DDCV in combination with the co-surfactants 1-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, cyclopentanol, and cyclohexanol for the analysis of N-methyl ephedrine, atenolol, metoprolol, ephedrine, pseudoephedrine, and synephrine. Ethyl acetate was applied as the microemulsion oil core, and as BGE, a 50-mM phosphate buffer with pH 7.0 was used. Cyclopentanol yielded the best enantioselectivity for three out of six compounds, 1-butanol for two, and 2-pentanol for one analyte. The most limited enantioselectivities for all compounds were observed with 1-pentanol and 1-hexanol. In a subsequent study," the simultaneous use of a chiral surfactant and chiral oil for MEEKC is discussed. Six combinations of DDVC (R, S, or racemic, 2.00% w/v), co-surfactant racemic 2-hexanol (1.65% v/v), and chiral oil dibutyl tartrate (d, L,or racemic, 1.23% v/v) were examined for the separation of the compounds mentioned above. Dual-chiral-ity microemulsions (emulsions in which the surfactant and oil are in opposite stereochemical configurations) provided both the largest and smallest enantioselectivities, as a result of small positive and negative synergies between the chiral microemulsion components. / -DDVC, 2-hexanol, and 5-dibutyl tartrate provided the highest enantioselectivity for all compounds except for metoprolol. 5-DDVC, 2-hexanol, and 5-dibutyl tartrate ranked lowest for all three ephedrine derivatives, while 5-DDVC, 2-hexanol, and R-dibutyl tartrate gave the lowest values for metoprolol and synephrine. 

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