Use of small-angle neutron scattering to investigate modifications of internal structure in self-assembled grains of nanoparticles synthesized by spray drying.

Micrometric spherical grains consisting of self-assembled silica nanoparticles have been synthesized by spray drying of colloidal suspension. Inter-particle correlation and available specific surface area of silica and void interfaces, in the assembled grains, were modified by addition of electrolyte in initial colloidal dispersion prior to self-assembly process but keeping the overall spherical shape of the assembled grains un-altered. While the external morphology of the assembled grains was probed by scanning electron microscopy, small-angle neutron scattering technique has been employed to investigate the modifications in the internal structure and the inter-particle correlation inside the assembled grains. It is revealed that a sticky hard sphere type of inter-particle correlation between the constituent particles gets altered to a fractal type of correlation with addition of electrolyte. Further, the specific surface area of the silica-void interface gets somewhat enhanced by addition of electrolyte and particularly at higher electrolyte concentration due to formation of some hollow and buckled assembled grains.