Evaporation-induced self assembly of nanoparticles in non-buckling regime: volume fraction dependent packing

Hierarchically structured micrometric spheres are synthesized by evaporation-induced self assembly of silica colloids using spray drying technique. Packing of nanoparticles during drying of droplets is an important issue. The motivation of the present work is to investigate the effects of concentration of initial colloidal dispersion on the packing of the nanoparticles in assembled grains in non-buckling regime of drying. It has been observed that the packing of nanoparticles inside the dried grains, even in the non-buckling regime, varies significantly with concentration. Although, the packing of nanoparticles remains uniform in an assembled grain at smaller concentration, the same becomes non-uniform at higher concentration. Further, the average packing fraction of the nanoparticles within the assembled grains, decreases with increasing colloidal concentration. These observations have been attributed to the modification in viscosity of the initial dispersion. Electron microscopy, light scattering measurements have been performed to probe overall morphology of the dried grains, while inter-particle correlation inside the grains has been investigated by small angle neutron scattering.