Microemulsions characterisation

Agostiano A, Catalano M, Curri ML, Della Monica M, Manna L, Vasanelli L (2000) Synthesis and structural characterisation of CdS nanoparticles prepared in a four-components water-in-oil microemulsion. Micron 31 253-258... 

Different surfactants are usually characterised by the solubility behaviour of their hydrophilic and hydrophobic molecule fraction in polar solvents, expressed by the HLB-value (hydrophilic-lipophilic-balance) of the surfactant. The HLB-value of a specific surfactant is often listed by the producer or can be easily calculated from listed increments [67]. If the water in a microemulsion contains electrolytes, the solubility of the surfactant in the water changes. It can be increased or decreased, depending on the kind of electrolyte [68,69]. The effect of electrolytes is explained by the HSAB principle (hard-soft-acid-base). For example, salts of hard acids and hard bases reduce the solubility of the surfactant in water. The solubility is increased by salts of soft acids and hard bases or by salts of hard acids and soft bases. Correspondingly, the solubility of the surfactant in water is increased by sodium alkyl sulfonates and decreased by sodium chloride or sodium sulfate. In the meantime, the physical interactions of the surfactant molecules and other components in microemulsions is well understood and the HSAB-principle was verified. The salts in water mainly influence the curvature of the surfactant film in a microemulsion. The curvature of the surfactant film can be expressed, analogous to the HLB-value, by the packing parameter Sp. The packing parameter is the ratio between the hydrophilic and lipophilic surfactant molecule part [70] ... 

P. P. Constantinides and J. P. Scalart, Formulation and physical characterisation of water-in-oil microemulsions containing long-versus medium chain glycerides, Int. J. Pharm. 758 57-68 (1997). 

Alany, R. G. (2001), Microemulsions as vehicles for ocular drug delivery Formulation, Physical-chemical characterisation and biological evaluation, Ph. D. thesis, University of Otago, Otago. 

Burnett, G.R. Rees, G.D. Steytler, D.C. Robinson, B.H. Pluorescence correlation spectroscopy of water-in-oil microemulsions an application in specific characterisation... 

Aboofazeh, R. Lawrence, M.J. Investigations into the formation and characterisation of phosphohpid microemulsions. II. Pseudo-ternary phase diagrams of systems containing water-lecithin-isopropyl myristate. Int. J. Pharm. 1994, 111, 63-72. 

Baker, R.C. Florence, A.T. Ottewill, R.H. Tadros, T.F. Investigations into the formation and characterisation of microemulsions 2. Light scattering, conductivity and viscosity studies of microemulsions. J. Colloid Interf. Sci. 1984, 100, 332-349. 

The most common definition of a microemulsion characterises it as a thermodynamically stable, transparent, optically isotropic, freely flowing surfactant mixture, often containing co-surfactants (e.g. alcohol) and added salts [37]. We restrict the definition further to non-crystalline (disordered) aggregates, since crystalline isotropic phases are better considered as liquid crystalline mesophases. Indeed, the most succinct description of a microemulsion would involve its microstructure. However, this has proven to be a very equivocal issue. So much so that until very recently it was widely believed that microemulsions were devoid of microstructure hence the thermod)mamic definition. 

Kim C-K, Ryuu S-A, Park K-M. Preparation and physicochemical characterisation of phase inverted water/oil microemulsion containing cyclosporin A. Int J Pharm 1997 147 131-134. 

Our approach to the preparation of supported combustion catalysts is different We applied w/o microemulsion eontaining water-soluble Pt compound directly on a formed catalytic support of defined shape. As the complete characterisation of catalysts with low concentration of platinum is often difficult, we prepared a set of catalysts with 0.3 wt. % Pt. But in addition, we prepared another set of catalysts with 0.1 wt. % Pt. Such catalysts are especially interesting for combustion of VOC, because the price of the catalysts is not so high. 

Table 2 comprises important details concerning microemulsions preparation, characterisation of calcined catalysts and their activity in combustion of toluene expressed... 

A. Figoli, W. F. C. Sager, Polymerised bicontinuous microemulsion (PBM) membranes preparation, characterisation and application, presented at Prague Meetings on Maeromolecules (2001) ISBN 80-85009-41-2. 

Dunn, C.M., Robinson, B.H. and Leng, RJ. (1990) Photon-correlation spectroscopy applied to the size characterisation of water-in-oil microemulsion systems stabilised by Aerosol-OT effect of change in counterion. Spectrochim. Acta, 46A, 1017-1025. 

CuS has also been prepared [ 36 ] by using Cu-ammonia complex and thiourea in alkaline pH in a water/cyclohexane/Triton X100/methylpropane-l-ol microemulsion. Other nonionic surfactants as well as ionic sodium dodecylsulphate were also used. Biswas et al. [29] synthesised CuS nanoparticles in water/cyclohexanone/Triton X100/i-propanol w/o microemulsion. The band gap of the material and the particle growth were determined from spectral and DLS measurements along with their general characterisation. 

Kreilgaard, M., Pedersen, E.J. and Jaroszewski, J.W. (2000) NMR characterisation and transdermal drug delivery potential of microemulsion systems. /. Control. Release, 69, 421-433. 

Samples were also taken from the diluted and the long float. The characterisation of the phase behaviour resulted for both floats in a three-phase state, which, in contrast to the short float, is not located at T = 37°C, but at T = 60°C as shown in Fig. 10.7. At the degreasing temperature T = 30°C now a fat-in-water microemulsion coexists with a fat-excess phase, which is turned into a stable fat-in-water emulsion via shearing. 

The results obtained from the characterisation of the phase behaviour and in the beam house imply that Eusapon OD is a suitable alternative allowing for an eco-friendly degreasing of animal skins. However, the understanding of the so far unidentified degreasing mechanism is the key goal for a continuous development of the degreasing process itself. In order to clarify the role of microemulsions in degreasing additional phase behaviour and interfacial tension measurements were conducted. 

For all systems we characterise as physico-chemists, the fundamental issue we deal with is that of whether we have a thermodynamically stable system or not. However, in the case of microemulsions, looking back we can see that it were the spectacular properties of microemulsions that called attention, while issues of whether the system was kinetically or thermodynamically stable were not in focus. Therefore, in the early work, a phase diagram approach, already established for surfactant systems in general, was not applied. 

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