Using Microemulsions: Formulation Based on Knowledge of Their Mesostructure

Abstract

Microemulsions, as thermodynamically stable mixtures of oil, water, and surfactant, are known and have been studied for more than 70 years. However, even today there are still quite a number of unclear aspects, and more recent research work has modified and extended our picture. This review gives a short overview of how the understanding of microemulsions has developed, the current view on their properties and structural features, and in particular, how they are related to applications. We also discuss more recent developments regarding nonclassical microemulsions such as surfactant-free (ultraflexible) microemulsions or ones containing uncommon solvents or amphiphiles (like antagonistic salts). These new findings challenge to some extent our previous understanding of microemulsions, which therefore has to be extended to look at the different types of microemulsions in a unified way. In particular, the flexibility of the amphiphilic film is the key property to classify different microemulsion types and their properties in this review. Such a classification of microemulsions requires a thorough determination of their structural properties, and therefore, the experimental methods to determine microemulsion structure and dynamics are reviewed briefly, with a particular emphasis on recent developments in the field of direct imaging by means of electron microscopy. Based on this classification of microemulsions, we then discuss their applications, where the application demands have to be met by the properties of the microemulsion, which in turn are controlled by the flexibility of their amphiphilic interface. Another frequently important aspect for applications is the control of the rheological properties. Normally, microemulsions are low viscous and therefore enhancing viscosity has to be achieved by either having high concentrations (often not wished for) or additives, which do not significantly interfere with the microemulsion. Accordingly, this review gives a comprehensive account of the properties of microemulsions, including most recent developments and bringing them together from a united viewpoint, with an emphasis on how this affects the way of formulating microemulsions for a given application with desired properties.

Mn doped Prussian blue nanoparticles for T1/T2 MR imaging, PA imaging and Fenton reaction enhanced mild temperature photothermal therapy of tumor

“…Microemulsion synthesis has been proved to be a convenient method for preparation nanoparticles [ 50 , 51 ]. Therefore, we prepared MnPB NPs via water-in-oil (w/o) microemulsion method as shown in Fig.…”

Molecular Forces in Liquid–Liquid Extraction

“…At equilibrium, the chemical potential of a extractant is assumed to be the same for the monomer and the micellar (aggregated) state. The area of contact at the nanoscale between polar and apolar regions is on the order of 1 nm 2 per aggregated molecule . The molecules present as monomers are not active for extraction and have no measurable microscopic area of contact.…”

“…The area of contact at the nanoscale between polar and apolar regions is on the order of 1 nm 2 per aggregated molecule. 104 The molecules present as monomers are not active for extraction and have no measurable microscopic area of contact. This active interface in the colloidal domain is at least 5 orders of magnitude higher than the macroscopic area of contact between the solvent and aqueous phases (shown in green in Figure 4).…”

Cryogenic Electron Microscopy Methodologies as Analytical Tools for the Study of Self-Assembled Pharmaceutics

“…Nanostructural characterization of microemulsions along a specific dilution line or at different compositions of oil and water may require complementarity of both cryo-EM methods, as demonstrated in the study of Davidovich et al [ 37 ]. More information on cryo-EM of microemulsions and the connection between the systems’ nanostructures and properties is given in a recent review by Gradzielski et al [ 38 ].…”