Nanocomposite Powders by Evaporation Driven Self Assembly During Spray Drying: Some New Insights on the Structure Modifications

摘要

Porous composite powders were prepared by spray drying silica and polybromostyrene nanoparticles. The structures in these powders were quantitatively investigated by Ultra Small Angle X-ray Scattering (USAXS), Thermo Gravimetric Analysis (TGA) and Nuclear Magnetic Resonance (NMR) measurements. It was found that the polybromostyrene latex is efficient in templating mesopores. However, the polybromostyrene remains almost completely in the interstitial micropores in the grain after the spray-drying process. The effect of the ratio of amount of latex to silica on the pore structure was studied. A post thermal treatment of the powders 250° to 750℃ has been applied. It was found that the hydrocarbon part of the polybromostyrene is decomposed and leaves the micropores at around 350℃. However, it is demonstrated that a significant amount of bromine remains in the interstitial micropores between the silica particles. At around 600℃ the nano-silica particles start to fuse together and coalescence of the micropores takes place. At higher temperature around 750℃ the micropore network totally disappears and growth in pore size occurs due to the coalescence of the mesopores with a significant decrease of the total porosity. During this process, the densification of the silica network is accompanied by a reduction of the specific surface area.