Application of flow-focusing to the break-up of an emulsion jet for the production of matrix-structured microparticles

Powder behaviour and performances are intimately related to particle attributes defined by the size, shape and structure of the individual particles making up the powder. The heterogeneous nature of the vast majority of powders reflected in the broad distribution of these particle attributes gives rise to the well-known difficulties in the prediction of powder behaviours. To achieve a better predictability and ultimate control of the performances, significant research efforts have recently been made towards the production of particles with controlled attributes, i.e. structured particles with a very narrow size distribution. This paper presents a new method for the production of monodisperse matrix-structured microcapsules using a simple in-house designed and fabricated macroscopic flow cell. The method combines flow-focusing with laminar jet break-up of a water-in-oil emulsion jet in a bulk water phase that produces monodisperse water-in-oil-in-water dispersion templates. The templates are then converted into solid microcapsules with a matrix structure by solvent evaporation. Results presented in the paper confirm a transition of flow regime from jetting to dripping when the outer to inner flow rate ratio reaches a critical value, accompanied by an increase in the size of the resultant droplets from the break-up. Importantly, the transition imposes a limit to the smallest size of monodisperse droplets each flow cell can produce through flow-focusing. The smallest monodisperse microcapsules produced from the flow cell used in this study through flow-focusing are 20 mu m in diameter. (c) 2008 Elsevier Ltd. All rights reserved.