Coating or encapsulation of nanoparticles is a major challenge due to the extremely small size, high surface energy, and high
surface area of the nanoparticles. In this paper we describe a new method using supercritical CO2 as an anti-solvent (SAS) for
nanoparticle coating/encapsulation. A model system, using silica nanoparticles as host particles and Eudragit polymer as the
coating material,was chosen for this purpose. The SAS process causes a heterogeneous polymer nucleation with the nanoparticles
acting as nuclei and a subsequent growth of polymer on the surface of the nanoparticles induced by mass transfer and phase
transition. A polymer matrix structure of encapsulated nanoparticles is formed by agglomeration of the coated nanoparticles.
Field emission scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy and Fourier
transform infrared spectroscopy were used to characterize the coated/encapsulated silica nanoparticles.