Preparation of highly concentrated nanostructured dispersions of controlled size

This article presents the use of a shearing procedure for the preparation of stable nanostructured dispersions of lipid mesophases. This new application of the shearing technique is compared with the well-established ultrasonication method for the emulsification of these mesophases in water in terms of particle size, particle size distribution and available concentration range. With a laboratory-built shear device based on a Couette cell, it was possible to produce high quantities of internally self-assembled emulsion particles of controlled size at concentrated hydrophobic phase contents (_o) of up to 70 wt%. The concentration limit of 70 wt% could be reached however, the maximum attainable concentration depended on the internal structure type of the particles. The limit was thus easily attained for emulsified microemulsions (EME) as well as for the emulsified inverse hexagonal phase (H₂), whereas it was found to be lower for emulsified discontinuous (Fd3m) and bicontinuous (Pn3m) cubic phases. Moreover, by shearing, it was possible to keep the size of the particles relatively constant when increasing _o, whereas the particle size significantly increased with _o when ultrasonication was employed. By means of ultrasonication, the hydrodynamic radius of the particles could be tuned linearly between 85 to 180 nm as a function of _o up to a maximum of 20 to 30 wt%. Below the maximum concentration limit, particles displayed a well-controlled size.