Non-aqueous castor oil-in-glycerin-in-castor oil double (o/o/o) Pickering emulsions: physico-chemical characterization and in vitro release study

Castor oil-in-glycerin-in-castor oil double (o/o/o) Pickering emulsions are successfully prepared and stabilized by only one type of silica nanoparticles possessing 50% silanol groups. The resulted emulsions exhibited excellent stability against coalescence for over a month. The apparent viscosity of these emulsions is explored as a function of silica nanoparticles concentration and globule volume fraction for the first time. Comprehensive physico-chemical studies of both simple and double emulsions are investigated. The flow behavior of these double emulsions (castor/gly./castor) followed the non-Newtonian shear thinning trend similar to that in simple emulsions (gly./castor). Both simple (gly./castor) and double (castor/gly./castor) emulsion types can be stabilized by one and the same silica nanoparticles during the catastrophic phase inversion (CPI) which occurred at glycerin drop volume fraction (ϕgly.) of 0.5–0.6 for the simple (gly./castor) emulsion and at glycerin globule volume fraction (ϕc/g) of 0.6–0.7 for the double (castor/gly./castor) emulsion. Both simple (gly./castor) and double (castor/gly./castor) emulsions were used to control the in vitro release of aspirin and the release profile was found to follow a zero-order kinetic for slow and prolonged release mechanism.