Microemulsion studies

For Cu(ll) in water adsorbed on silica gels it was reported 5 that in gels with small pores isolated hydrated ions are detected at 77 K5 in pores larger than -4 nm a broad signal is superimposed on the spectrum of isolated ions. The appearance of the broad signal indicates aggregation of cations and the presence of bulk or freezable water. In a recent publication the Cu(ll) probe was used to test the possibility of ice formation in microemulsions, jce formation was detected in one of the microemulsions studied for very slow cooling rates from -300 K to 77 K. 

B. Lindman and U. Olsson. Structure of microemulsions studied by NMR. Berichte Der Bunsen-Gesellschaft-Phys. Chem. Chem. Phys., 100(3) 344—363, 1996. 

The microemulsions studied show a single resonance for the alpha-carbon appearing midway between those of its expected model environments. The diffusion of cosurfactant within microemulsions is very rapid on an NMR time scale as has been confirmed in a series of studies (27,28,29). In this case, the observed chemical shift is a weighted average of those of the different environments in which the cosurfactant is located. For our system, the observed shift could be represented as... 

Eastoe J, Cazelles BMH, Ste5Tler DC, Holmes JD, Pitt AR, Wear TJ, Heenan RK. Water-in-C02 microemulsions studied by small-angle neutron scattering. Langmuir 1997 13 6980-6984. 

Arleth, L. and Pedersen, J.S. (2001) Droplet polydispersity and shape fluctuations in AOT [bis(2-ethylhexyl)sulfosuccinate sodium salt] microemulsions studied by contrast variation small-angle neutron scattering. Phys. Rev. E, 63, 61406-61423. 

Bagger-Jorgensen, H., Olsson, U. and Mortensen, K. (1997) Microstructure in a ternary microemulsion studied by small angle neutron scattering. Langmuir, 13, 1413-1421. 

Eastoe, Julian Gazelles, Beatrice M. H. Steytler, David C. Holmes, Justin D. Pitt, Alan R. Wear, Trevor J. Heenan, Richard K. Water-in-C02 Microemulsions Studied by Small-Angle Neutron Scattering. Langmuir 1997, 13(26), 6980-6984. 

Three of the microemulsions studied were characterized by conductivity measurements AOT-heptane-water, Triton X-lOO-decanol-water, and CTAB-hexanol-water. The last two were also characterized by cryofracture measurements. 

For all the microemulsions studied, the presence of only one resonance line for each carbon atom is characteristic of a rapid exchange of molecules between several sites (interface, organic phase, vicinity of the paramagnetic ion, etc.) [2-4]. Figure 3 illustrates the variation of the chemical shifts (A5 = dm — b, where 6m and b are the chemical shifts in the presence and absence of paramagnetic ions, respectively). 

For example, SK F-106760 and SK F-l 10679, both water-woluble RGD fibrinogen receptor antagonists, were formulated in microemulsions at pharmaceutically relevant levels, and their uptake after intraduodenal administration was investigated [39-41]. It was found that the presence of the SK F-l 10679 peptide in varying concentrations did not influence the structure of the W/O microemulsion studied. Furthermore, the bioavailability of SK F-106760 was increased dramatically for the microemulsion formulations compared to that of the aqueous solutions, as can be seen in Fig. 5. 

J. Georges and J. W. Chen. Microemulsion studies correlation between viscosity, electrical conductivity and electrochemical and fluorescent probe measurements. Colloid Potym, Sci 264 896-902, 1986. 

Of the parameters entering Eqs (5)-(7) we have a knowledge of Hq and K from the microemulsion studies, while K is irrelevant when considering changes in Gp. Surface tensions have been extensively studied for microemulsions and it has been demonstrated that y has a deep minimum at balanced conditions and that its value is dependent on the spontaneous cmvatme of the film. Under droplet microemulsion conditions ... 

Obviously, all of the proposed relationships discussed so far are linear. However, there are also very clear examples where a strong linear relationship was not so obvious, at least not for the total range of w values of the microemulsions studied by different workers. Zulauf and Eicke [76] clearly showed from photon correlation spectroscopy curvilinear relationships between w (up to 50) and the Stokes radius of the water pool in the system AOT/isooctane /H2O (Fig. 3.11). The curves, however, could be divided into linear parts with different slopes. Similarly, acoustic spectroscopic studies of the system A0T/heptane/H20 by Wines et al. [ 152] exhibited a non-linear relationship between the mean diameter of water droplets (from about 8 nm to 17 nm) and the w value (10 to 60) there was no appreciable change from w = 10 to w = 20, but this part of the curve could be taken as linear with a very gentle slope (Fig. 3.12). In the system AOT/isooctane/ H2O, Chen et al. [153] found a linear relationship only up to w = 10. 

Water-in-C02 microemulsions studied by small-angle neutron scattering, Langmuir 13,6980-6984 (1997). 

J.P. Le Pesant, R. Ober and M. Lagiies for their kind collaboration in the microemulsions study. 

Shukla, A. and Neubert, R.H.H. 2006 Diffusion behavior of pharmaceutical o/w microemulsions studied by dynamic light scattering. Colloid Polym. Sci. 284 568-573. 

Yaghmur, A., Aserin, A., Antalek, B., and Garti, N. 2003 Microstructure considerations of new five-component Winsor IV food-grade microemulsions studied by pulsed gradient spin-Echo NMR, conductivity, and viscosity, Langmuir 19 1063-1068. 

Garti, N.,Anserin, A., Ezrahi, S., Tiunova, L, and Berkovic, B. 1996. Water behaviour in nonionic surfactant systems I Subzero temperature behavior of water in nonionic microemulsions studied by DSC. J. Colloid Interface Sci., 178, 60-68. 

Fletcher, P.D.I., Rees, G.D., Robinson, B.H., Freedman, R.B. 1985. Kinetic properties of a-chymotrypsin in water-in-oU microemulsions Studies with a variety of substrates and microemulsion systems. Biochem. Biophys. Acta 832, 204-214. 

To study the optical and photophysical properties of in microemulsion we have used Ti02 NPs which are synthesized by solgel method as described earlier. The microemulsion was prepared using the following composition (2g NaLS/1.8cc water/ 46.5 cc cyclohexane/9.5 cc 1-butanol). The diameter of this water pool is around 4-5 nm. Pileni et al. [22] have shown an empirical relation between Wg and r as r = 1.5 Wq (where r is the radius of the water pool for microemulsion). According to Adhikari et al. [23], the water droplet size is 4.2nm in the present microemulsion studied. T1O2 NPs in this study can just fit in the water pool (Figure 18.1). 

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