(275a) Hybrid Bilayer Hollow Submicron Particles with Carbon and Silica Nanoshells Fabricated Through a Template Free Process and Their Applications As Multifunctional Materials

We present a facile aerosol based method to create a hollow particulate system with a composite bilayer shell. The external layer is silica while the internal layer is carbon, thus creating an amphiphilic shell with an intrinsically hydrophilic external surface and a hydrophobic internal surface. The particles are obtained using a new concept of forming a silica shell extremely rapidly and locking in other precursors in the interior of an aerosol droplet.  This is done by exploiting salt bridging concepts to confine a surfactant (CTAB) and carbon precursors together with iron oxides in the interior of a droplet while a silica shell is allowed to form on the droplet surface. Subsequent pyrolysis results in a buildup of internal pressure forcing carbon formation as a second layer adjoining the silica shell.  The synthesis method is expected to be a general approach to fabricate a variety of hybrid double layer hollow microspheres with unique properties. In addition, the incorporation of magnetic iron oxide into the shells opens up opportunities in external stimuli responsive materials. Hollow nano and microparticles have a variety of applications in encapsulation, catalysis, separation and controlled drug release. The aerosol based process is intrinsically scalable and overcomes many of the drawbacks of traditional methods of making hollow structures through multiple steps of forming layers over sacrificial particle cores.