Microemulsion-based media as novel drug delivery systems

We identify the physical mechanism through which newly developed quaternary ammonium salt (QAS) deposit control additives (DCAs) affect the rheological properties of cavitating turbulent flows, resulting in an increase in the volumetric efficiency of clean injectors fuelled with diesel or biodiesel fuels. Quaternary ammonium surfactants with appropriate counterions can be very effective in reducing the turbulent drag in aqueous solutions, however, less is known about the effect of such surfactants in oil-based solvents or in cavitating flow conditions. Small-angle neutron scattering (SANS) investigations show that in traditional DCA fuel compositions only reverse spherical micelles form, whereas reverse cylindrical micelles are detected by blending the fuel with the QAS additive. Moreover, experiments utilising X-ray micro computed tomography (micro-CT) in nozzle replicas, quantify that in cavitation regions the liquid fraction is increased in the presence of the QAS additive. Furthermore, high-flux X-ray phase contrast imaging (XPCI) measurements identify a flow stabilization effect in the region of vortex cavitation by the QAS additive. The effect of the formation of cylindrical micelles is reproduced with computational fluid dynamics (CFD) simulations by including viscoelastic characteristics for the flow. It is demonstrated that viscoelasticity can reduce turbulence and suppress cavitation, and subsequently increase the injector’s volumetric efficiency.

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Turbulence and Cavitation Suppression by Quaternary Ammonium Salt Additives.

Recent advances in nanoparticle synthesis with reversed micelles.

Zinc oxide nanoparticles: Synthesis, antiseptic activity and toxicity mechanism.

In the past twenty five years, microemulsions have been the focus of extensive research worldwide due to their importance in a variety of technological applications. These applications include enhanced oil recovery, combustion, cosmetics, pharmaceuticals, agriculture, metal cutting, lubrication, food, enzymatic catalysis, organic and bio-organic reactions, chemical synthesis of nanoparticles etc. The basic purpose of this review is intended to provide the most important features of microemulsions and their applications. Emphasis is placed on recent works, however, the reference list is by no means complete. In order to limit the size of the review, a more or less arbitary selection has been made with respect to examples chosen from literature. The review is started with a brief introduction and focussed with definition, structure, type, formation characteristics, stability, phase behavior and the effect of additives, pressure, temperature on the phase behavior of microemulsion. In addition, the p...

Microemulsions: an overview

The sodium salt of the di-chained anionic surfactant bis-2-ethylhexylsulfosuccinate [Aerosol-OT or Na(AOT)] stabilises essentially monodisperse, spherical water-in-oil microemulsion (w/o) droplets in alkanes over a wide range of pressure, temperature and composition. In order to investigate the effect of change in counterion charge and size on the microemulsion properties, we have replaced the Na+ counterion by doubly charged ions. The surfactant is then M2+(AOT)2·nH2O: M is from the series Mg2+, Ca2+, Co2+, Ni2+, Cu2+ and Zn2+, and n is the number of water ligands associated with the surfactant molecule. The value of n was determined by FTIR and depends on M2+, but can be between 2 and 8 per molecule of M2+(AOT)2 depending on the nature of M. The ion replacement, assessed by UV–VIS spectrophotometry, is ca. 100% efficient. The effect of temperature on the phase stability of the single-phase M2+(AOT)2 water-in-oil (w/o) microemulsion systems is negligible, in contrast to that observed for the corresponding Na(AOT) system. The structure and properties of the microemulsion are found to be dependent on the counterion identity. Small-angle neutron scattering (SANS) and viscosity measurements provide evidence for the existence of rod-shaped aggregates for Co2+, Ni2+, Cu2+ and Zn2+ at low water constants given by w=[H2O]/[AOT]≈ 5, whilst for Mg2+ and Ca2+ spherical aggregates are present as for Na+. On further addition of water at constant surfactant concentration (w > 10) with Co2+, Ni2+, Cu2+ and Zn2+ the aggregates undergo a shape change, and a more spherical structure is favoured. The results may be explained in terms of the interaction of the different counterions with the SO–3 head group of the surfactant.

Variation of surfactant counterion and its effect on the structure and properties of Aerosol-OT-based water-in-oil microemulsions

Photon-correlation spectroscopy applied to the size characterization of water-in-oil microemulsion systems stabilized by Aerosol-OT; effect of change in counterion

The He(I)/Ne(I) angular distribution photoelectron spectra of allene show no change in asymmetry parameter associated with the Jahn–Teller splitting of the first band. Across the second spectral region, in contrast, there is a marked change in β-values, so confirming its assignment to overlapping second and third bands. This variation in asymmetry parameter is, however, completely different at the two ionizing wavelengths. This is attributed, unusually, to the occurrence of autoionization in the He(I)[but not Ne(I)] spectrum.

Frank J. Leng

Papers

Variation of surfactant counterion and its effect on the structure and properties of Aerosol-OT-based water-in-oil microemulsions

Photon-correlation spectroscopy applied to the size characterization of water-in-oil microemulsion systems stabilized by Aerosol-OT; effect of change in counterion

Angular-distribution He(I)/Ne(I) photoelectron spectra of allene