Ultra-porous hollow particles

Hollow particles with porous shells have been prepared by a simple modification to the surfactant-free polymerisation of styrene by the incorporation of water-soluble natural polymers and the use of high stirring speeds. The particle morphology has been characterised by scanning electron microscopy (SEM). When styrene is polymerised in the presence of either carboxymethyl cellulose (CMC) or sodium alginate at high stirring speeds, small homogeneous (solid) particles (diameter ~200 nm) and large porous particles (diameter~10 m) are both formed. However, at low stirring speeds only the small homogeneous (solid) particles are formed. Further, only the small homogeneous (solid) particles are formed when non-adsorbing polymers such as starch and poly(vinyl alcohol) are present. In contrast, polymers that strongly adsorb onto polystyrene particles cause the polymerising mixture to flocculate. It is proposed that the porous character is a direct result of the polymerisation of a multiple emulsion in the presence of a depletion interaction. Moreover, addition of a high concentration of surfactant to the CMC system simply results in the spherical homogenous particles, suggesting that the surfactant removes the depletion effect