The mobility of water in water/Aerosol OT (AOT)/isooctane reverse micelles has been investigated via polar solvation dynamics measurements using ultrafast, time-resolved fluorescence-upconversion spectroscopy. For the smallest reverse micelles studied, w0 = 1.1, no solvation dynamics are observed on the time scale of the instrument, suggesting that the water is essentially frozen. As w0 increases, the mobility of water increases, and the time-correlation functions exhibit multiexponential decays. A subpicosecond component is observed on a time scale similar to that of diffusive bulk-water motion.1 The other components decay on time scales of a few picoseconds to hundreds of picoseconds. The amplitude of the solvent response increases as w0 increases, which is attributed to increased mobility of the water inside the reverse micelles. Because the micellar interior is highly ionic, the solvation dynamics of coumarin 343 in a 1 M Na+ (Na2SO4) solution were also investigated to compare the dynamics of water in...

Water Immobilization at Surfactant Interfaces in Reverse Micelles

We report a systematic FTIR study of the perturbation of water "sorbed" into the polymers PET and PVC as a function of crystallinity (PET) or plasticizer content (PVC). Band shapes of the composite v(OH) band of H2O obtained by the ATR technique have been fitted to individual components,corresponding to those recently found for pure water itself. A detailed quantitative analysis of the frequency shifts and relative intensties has led to conclusion that these component bands show direct evidence for the breaking of the water network in the polymer matrix and that this process depends on the polymer chemical and/or physical properties, Evidence is also found for interactions of water with the polymer at the lower end of the hydrogen bond interaction scale. The component band relative intensities (compared with those of pure water) have been used to compute an intensity enhancement parameter, P, which is a measure of the perturbation of a particular water distribution due to dissolution in the polymer matrix. For PET, P varies systematically with density, reflecting the ability of water to penetrate the polymer microstructure. For PVC the plasticizer content (and hence T-g) has considerable influence on the sorption (and swelling) process and on the equilibrium content and state of water. Thus, ATR-FTIR has been used for the first time to demonstrate, via intensity enhancement, the extent of electronic perturbation at a polymer/water interface.

FTIR-ATR studies of the structure and dynamics of water molecules in polymeric matrixes. A comparison of PET and PVC

Polar solvation dynamics of water sequestered inside Aerosol OT (AOT) reverse micelles have been investigated as a function of the surfactant countercation, specifically replacing Na+ for K+ and Ca2+. For Ca-AOT reverse micelles, the solvation dynamics for the smallest micelles probed occurs on a subnanosecond time scale. The K-AOT reverse micelles display an additional ultrafast component that is attributable to bulklike water motion. As previously reported for Na-AOT reverse micelles [Riter, Willard, and Levinger, J. Phys. Chem. B 102, 2705 (1998)], solvent mobility increases with increasing micellar size for both Ca-AOT and K-AOT reverse micelles. The solvation dynamics in strongly ionic aqueous solutions of Ca2+ and K+ have also been investigated. The 10 M electrolyte solutions display water motion on significantly shorter time scales with substantial ultrafast components. These results show that the micellar interfacial structure plays a significant role in immobilizing intramicellar water and that solvent immobilization in the reverse micelles is not merely a result of solvent–ion interactions.

Influence of restricted environment and ionic interactions on water solvation dynamics

Analysis of Tween based microemulsion in the presence of TB drug rifampicin.

Purpose
The purpose of present study is to formulate microemulsion composed of oleic acid, phosphate buffer, Tween 80, ethanol and to investigate its potential as drug delivery system for an antitubercular drug isoniazid.

Incorporation of Antitubercular Drug Isoniazid in Pharmaceutically Accepted Microemulsion: Effect on Microstructure and Physical Parameters

FT-IR spectra in the hydroxyl region in reversed micelles where the sodium counterions of the surfactant Aerosol-OT have been replaced by Ca2+ and Zn2+ ions are presented. The IR spectra, taken as a function of the molar ratio R = [H2O]/[surfactant], are analzyed in the framework of a twostate model for the water molecules in which the O-H vibration can be split into two contributions: one originated by the water “tightly-bonded” to the surfactant ions, and the other induced by the “bulk” water of the micellar water pool. We also evaluate the percentage a(R) of the bond water in the micellar growth process. Furthermore, an explanation of the O-H stretching band features is suggested by comparison between our spectra and those simulated through an MD “experiment”.

V. Turco-Liveri

Papers

Local hydration effects in reversed micellar aggregates