The synthesis, characterisation and properties of self- assembled hollow and low density microspheres.

摘要

Hollow low density microspheres were prepared by adsorbing kaolin nanoparticles onto a polystyrene (PS) template. A cationic polyelectrolyte, poly(diallydimethylammonium chloride), was initially adsorbed on the PS to render the surface cationic enabling the kaolin nanoparticles to form a shell structure due to electrostatic attraction forces. An increase in ionic strength by the addition of 0.1 M NaCl increased the amount of polyelectrolyte adsorbed at the PS surface. Solvent relaxation NMR experiments indicated that solvent molecules were bound at the PS surface suggesting attached polymer chains. Zeta potential experiments indicated a change in the surface potential at the PS interface due to the addition of a polyelectrolyte, as little as 0.1 g m-2 of polyelectrolyte was required to change the PS surface potential. Surface saturation of the PS resulted in a zeta potential of 63.5 (pm)2.6 mV, at pH 6.6 (pm)0.2. Kaolin adsorption was determined by reduced sediment volume experiments and observed by the use of scanning electron microscopy (SEM). The influence of an increase in the kaolin ratio and the calcination process on the microsphere structure was investigated. When calcined at 1000 ºC for 60 min the microsphere properties exhibited a particle size (d50) of 11.2 (pm)0.4 (mu)m and a bulk density of 0.13 (pm)0.01 g/cm3. The internal structure of the calcined microspheres were characterised by the use of SEM and focused ion beam (FIB) instruments. The characteristic properties of the calcined kaolin microspheres were determined by thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS).