Surfactant media

Generation of nanoparticles under Langmuir monolayers and within LB films arose from earlier efforts to form nanoparticles within reverse micelles, microemulsions, and vesicles [89]. Semiconductor nanoparticles formed in surfactant media have been explored as photocatalytic systems [90]. One motivation for placing nanoparticles within the organic matrix of a LB film is to construct a superlattice of nanoparticles such that the optical properties of the nanoparticles associated with quantum confinement are preserved. If mono-layers of capped nanoparticles are transferred, a nanoparticle superlattice can be con-... 

Zhang and Rusling [66] employed a stable, conductive, bicontinuous microemulsion of surfactant/oil/water as a medium for catalytic dechlorination of PCBs at about 1 mA cm-2 on Pb cathodes. The major products were biphenyl and its reduced alkylbenzene derivatives, which are much less toxic than PCBs. Zinc phthalocyanine provided better catalysis than nickel phthalocyanine tetrasulfonate. The current efficiency was about 20% for 4,4 -DCB and about 40% for the most heavily chlorinated PCB mixture. A nearly complete dechlorination of 100 mg of Aroclor 1260 with 60% Cl was achieved in 18 hr. Electrochemical dehalogenation was thus shown to be feasible in water-based surfactant media, providing a lower-cost, safer alternative to toxic organic solvents. 

Micellar-Enhanced Detection in Separation Science. In several instances, the use of appropriate surfactant media allows for enhanced and/or new modes for chromatographic detection. Most of the work has been in the area of spectroscopy. For example, it is well known that the presence of suitable surfactant micelles can significantly increase the absorbance of metal complexes (4,8,345). 

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). 

Lastly, it may be possible to recover some analytes from the micellar/surfactant media by distillation. Several patent reports claim that materials (mostly essential or edible oils) can be recovered from highly concentrated micelles in this manner (520.521). The abstracts are too vague to judge the relative merit of this procedure or whether it is applicable to actual separation science problems. Further work is obviously required in this area. 

M. Colladon, A. Scarso, G. Strukul, Towards a greener epoxidation method. Use of water-surfactant media and catalyst recycling in the platinum-catalyzed asymmetric epoxidation of terminal alkenes with hydrogen peroxide, Adv. Synth. Catal. 349 (2007) 797. 

AUtan, M. et al.. Zeta potentials of perlite samples in various electrolyte and surfactant media. Colloid.s Surf. A, 259, 155, 2005. 

De, S. and Girigoswami, A. 2004, Fluorescence resonance energy transfer-a spectroscopic probe for organized surfactant media. Journal of Colloidal Interface Science 271,485-495. 

In Sect. 2.7.3.7.1, appropriate control of polymer composition of a redox polymer (PVF) was shown to lead to the introduction of viscoelastic phenomena and to thermal sensitivity. For polypyrrole, deposition from micellar surfactant media (dodecylsulfate and dodecylbenzenesul-fonate) also leads to changes in film morphology and viscoelastic behavior [139]. 

Researches on the surfactant effect of Ru(bpy)3 ECL have attracted extensive interest. Soluble Ru(bpy)3 in aqueous nonionic surfactant solutions leads to significant and potentially useful changes in the ECL properties. For example, up to eight-fold increases in ECL efficiency were observed in surfactant media upon oxidation of Ru(bpy)3 and TPrA (TPrA = tri-n-propylamine). The precise mechanism of the surfactant effect is still under study, but it appears that the adsorption of surfactant on the electrode surface should be responsible for these surfactant effects. The dramatic increases in ECL intensity, coupled with work on more efficient ECL labels and co-reactants, may have profound impacts on the sensitivity of ECL for a variety of applications. 

Kirchhoff et al. [27] investigated the factors influencing electro-analytical measurements in aqueous surfactant media and found that anionic SDS, cationic CTAB and nonionic Triton X-100 possess a wide potential window with low background currents within which electrochemical measurements can be conducted. While surfactants adsorb onto electrode surface, electron transfer can still occur between solute and electrode surface. 

J.R. Kirchhoff, E. Deutsch and W.R. Heineman, Factors Influencing Electroanalytical Measurements in Aqueous Surfactant Media, Anal. Lett, 22 1323 (1989). 

Jain R, Dwivedi A, Mishra R (2009) Adsorptive stripping voltammetric behavior of nortriptyline hydrochloride and its determination in surfactant media. Laugmuir 25(17) 10364-10369 Roth KM, Lindsey JS, Bocian DF, Huhr WG (2002) Characterization of charge storage in redox-active self-assembled monolayers. Laugmuir 18(10) 4030 040... 

Ziyatdinova G, Ziganshina E, Budnikov H (2012) Surfactant media for constant-current coulometry. Application for the determination of antioxidants in pharmaceuticals. Analytica Chimica Acta 744 23-28... 

CoUadon, M., Scarso, A. and Strukul, G. (2007). Towards a Greener Epoxidation Method Use of Water-Surfactant Media and Catalyst Recycling in the Platinum-Catalyzed Asymmetric Epoxidation of Terminal Alkenes with Hydrogen Peroxide, Synth. Catal., 349, pp. 797-801. 

Brahman, P.K., et al., Voltammetric determination of anticancer drug flutamide in surfactant media at polymer film modified carbon paste electrode. Colloids Surf., A, 2012. 396 p. 8-15. 

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