Producion of Nanoparticle Assemblies by Electro-Spraying and Freeze-Drying of Colloids: A New Method to Resolve Handling Problem of Nanoparticles

To resolv e handling problem of nan oparticles, due to their small size, a newmethodology of elec tro-sp ray ing and freeze-drying was developed f or collo idal nanoparticles ojsilica and titania to transform them to solid macr o-scale nanoparticle assem blies. the ass emblieswere then redispersed in an aqueous system to investigate the effect oj formulation oj originalsolutions and the proc ess parameters on reversi bili ty of the system to a stabilised colloidalcondition. the electro-spray ing was emp loyed to control the size oj droplets and consequently thesiz e ofnan oparticle ass emblies in the freeze-drying. high speed digital video recording ofthe sp raypro cess revealed that within 0 narrow range oj voltage, the size oj droplets redu ced sharply to aminimum valu e, where a narrow size distribution was obtained. non-destructive structural analysisof the freeze-dried nanoparticle assemblies usin g x-ray micro-tomography represented differentstructures oj the nanoparticle assemblies depending on type oj nanoparticles. the stability analysisoj redispersed nanoparticles in water (using centrifugal stability analys er) and their sizedistribution (obtained by nano-sizer) showed different stability conditions. these conditions wereaffected by physi cochemical prop erti es oj nanoparticle ass emblies and process parameters.in terms oftitania, it wasfound that with an appr opriate fo rmulation a/ peg solution (as binder 0/assemblies) and op timum size oj the nanoparticle assemblies it was possible to produce assemblieshaving adequate s trength and good re-dispersion properties.