The rotating diffusion cell is used to study the release of H+ from a water-in-oil microemulsion, stabilised with Aerosol-OT (AOT), into a coexisting aqueous phase. By measuring the release of H+ as a function of the rotation speed, the effects of mass transport can be separated, and rate constants for the kinetics of the transfer at the interface can be determined. With increasing concentration of droplets the rate reaches a limiting value. Measurements of the drop size, using photon correlation spectroscopy, allow the geometry of and the number of protons carried by each droplet to be found. The kinetic results are explained by a model in which the droplets first adsorb on the interface according to a Langmuir isotherm, and then in the rate-limiting step merge with the aqueous phase. A simple theoretical model is presented which compares this heterogeneous process with the equivalent homogeneous reaction, in which H+ is transferred between two droplets in the same phase. Again the process is separated into an association step, followed by a rate-limiting fusion of the droplets. In either case the association pre-equilibrium is found to be larger than the statistical value, and the rate-limiting fusion has a first-order rate constant in the range 3 x 102 to 103 s-1.

The self-assembly of nanoparticles into higher organizations in a controlled manner has critical importance for the utility of the unique properties of nanoparticles. The behavior of magnetic Fe(3)O(4) nanoparticles (MNPs) with an average size of 6 nm under an enhanced magnetic force is reported. Upon evaporation of the solvent where the MNPs are suspended, formation of unique micrometer-sized structures is achieved only when there is a patterned surface constructed from sub-micrometer size magnetic beads in between the applied magnetic field and the MNPs. The preliminary results indicate that the combined effect of magnetic field and evaporation rate might help the control of nanoparticle behavior on surfaces and interfaces in constructing higher structures.

Unilamellar liposomes, prepared from synthetic lipid mixture of DMPC and DMPG either by sonication or extrusion, were used to entrap water soluble and water insoluble molecules to investigate the efficacy of encapsulation by different liposome preparation methods. In the case of entrapment of hydrophilic protein cytochrome-C, the solutions were subjected to a series of ultrafiltration steps to eliminate any free protein outside the vesicles. It was observed that the protein could be encapsulated by the vesicles only if cholesterol was present in the bilayer. The release of cytochrome-C was observed spectrophotometrically upon vesicle-breakdown. The amount of protein encapsulated depended on the method of preparation and was found to be 10 times greater in extruded liposomes compared to those produced by sonication. Hydrophobic Vitamin E, on the other hand, could be encapsulated in the liposome bilayer, independently of the presence of cholesterol and the method of preparation. These fundamental results can be used to develop more efficient drug encapsulations and to have better understanding about their release.

We report the photophysical properties of 3,3 0 -diethyl-5,5 0 -dichloro-9-phenylthiacarbocyanine (DDPT) in methanolin-oil (m/o) reverse micellar systems which form methanol droplets stabilized with anionic surfactant aerosol-OT (AOT) in n-heptane. The fluorescence quantum yield of DDPT is enhanced by a factor of 17 in the methanol droplet in comparison with bulk methanol. The fluorescence lifetimes of DDPT in m/o reverse micelles are prolonged up to 2.2 ns with increasing molar ratio of methanol to surfactant (w 0 =[MeOH]/[AOT]), whereas the fluorescence lifetime of DDPT in bulk methanol is 75 ps. The non-radiative rate constants of DDPT in the droplets are decreased by a factor of 40, resulting in a remarkable enhancement in quantum yields, indicating that internal motions of DDPT in the droplets are significantly reduced due to strong electrostatic interactions between the positively charged DDPT and the negatively charged sulfonate head-groups of AOT and the spatial confinement induced by the reverse micellar structure. r

The forward transfer kinetics of a water-soluble cationic dye (dimidium) across the planar interface from a conjugate aqueous phase to a water-in-oil (w/o) microemulsion phase (formed using the anionic surfactant Aerosol-OT) have been investigated by means of a rotating diffusion cell. By measurement of the solute flux as a function of rotation speed of the diffusion cell membrane, the influence of mass transport effects to and from the interface could be controlled and eliminated by extrapolation to infinite rotation speed. The rate of forward transfer was linearly proportional to the concentration of solute in the aqueous phase; i.e., it was not possible to saturate the aqueous side of the interface. The rate, however, was found to reach a limiting value on increasing the concentration of nano water droplets in the microemulsion phase. This is explained by a transport model in which the dye initially partitions to the aqueous side of the interface; it then enters the organic phase inside a forming water droplet. The rate of back transfer of H + from a microemulsion droplet phase into a coexisting water phase has also been studied as a function of droplet concentration and temperature. These results extend previous measurements on the same system. It is shown that enthalpy-entropy compensation effects operate for the rate-determining step. In our proposed model for defining dynamics of interface transfer from or to an aqueous phase in Winsor-II systems, the rate-determining step is the same for forward and back transfer and is concerned with droplet coalescence with the interface.