Hollow microspheres with binary colloidal and polymeric membrane: Effect of polymer and particle concentrations

We report here the preparation of hollow microspheres with a binary shell structure consisting of a precipitated polymer film with a layer of colloidal particles embedded on its outer surface. We recently demonstrated a method for the preparation of microspheres from solid-stabilised emulsion templates using various colloidal particle systems as emulsifiers. In the present work we use colloidal silica as an emulsifier for the preparation of the emulsion template for the microspheres and study the effect of polymer and particle concentrations on the obtained structures. Observations using optical microscopy showed that decreasing the polymer concentration led to a reduction in the capsule wall thickness and apparent strength of the microspheres when dried. Importantly, all microspheres preserved their integrity when in suspension. SEM studies confirmed the differences observed in the thickness of the precipitated film at the oil/water interface. In addition, we also demonstrate that a larger particle concentration leads to microspheres with a lower degree of porosity.