Properties and Applications of Microemulsions

Abstract

Microemulsions are thermodynamically stable, fluid, optically clear dispersions of two immiscible liquids. Recent interest in microemulsion systems has resulted from their utility in a broad range of applications including enhanced oil recovery, consumer and pharmaceutical formulations, nanoparticle synthesis, and chemical reaction media. However, the high levels typically required to ensure complete microemulsification and formulation stability often result in unacceptably high residue, contaminant levels, and formulation cost. One way to reduce surfactant requirements in microemulsion systems is through the use of efficient surfactants and interfacially active cosurfactants. We have explored and developed microemulsion systems based on efficient anionic surfactants and glycol ether cosurfactants that are stable to temperature and compositional changes and yet employ low levels of non‐volatile surfactants. These microemulsion systems are finding utility in a range of applications, including consumer and industrial cleaning formulations, chemical reaction media, polymerization, and active ingredient delivery.

Water in soybean oil microemulsions as medium for electrochemical measurements

“…Considering that water droplets are surrounded by a film of nonpolar tails of dodecyl sulfate anions and amyl or isoamyl chains, 14 its diffusion through the continuous oil medium must be slower than the one for Fc molecules. On the other hand, the net positive charge in the water droplets 36 is probably the reason for the decrease in the limiting current observed for water oxidation in the presence of Fc (see Figure 5).…”

“…Due to the small interfacial tension, usually smaller than 0.001 dyn cm -1 , these systems are able to dissolve a high number of substances. 7,14,16 The microstructure of ME has been elucidated by various techniques, as for example static and dynamic light scattering, dielectric relaxation, time-resolved fluorescence 629 Water in Soybean Oil Microemulsions as Medium for Electrochemical Measurements Vol. 14, No.…”

“…[9][10][11][12] Their behavior is similar to the one of polar organic solvents and, although apparently homogeneous under visual observation, ME are actually microheterogeneous (perhaps nanoheterogeneous would be a better term) systems formed of particles with diameters in the order of 5 to 100 nm suspended in a continuous phase. 8,[13][14][15] The transparency showed by these systems is due to the fact that the size of the particles is much smaller than the wavelengths of radiation in the visible region. 16 The conducting properties of ME are given mainly by the surfactant or by the addition of a supporting electrolyte.…”

“…Due to the small interfacial tension, usually smaller than 0.001 dyn cm -1 , these systems are able to dissolve a high number of substances. 7,14,16 The microstructure of ME has been elucidated by various techniques, as for example static and dynamic light scattering, dielectric relaxation, time-resolved fluorescence or phosphorescence quenching, electric field or temperature jump, small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). These techniques can afford fruitful information about the core and surface monolayer structure, the particle size distribution, the polydispersity, the droplet clustering and diffusion dynamics, the inter-droplet exchange rate and the fluidity of the monolayer.…”

“…5,17,18 The rather classical methods of characterization through viscosity, interfacial tension, conductivity, turbidity and osmotic pressure measurements are still very reliable and informative. 14,[18][19][20][21] Particularly, the knowledge of the dynamic properties of the suspended droplets is very important in understanding the conductivity, chemical reactions and mass transfer processes occurring in these media. 18 A stable homogeneous mixture is transparent, whereas an unstable not homogeneous mixture is turbid unless the components of the mixture have identical refractive indexes.…”