Formation of hollow spherical and doughnut microcapsules by evaporation induced self-assembly of nanoparticles: effects of particle size and polydispersity

Abstract

Understanding the role of various physicochemical parameters is essential in order to control the microstructure during evaporation induced self-assembly in drying colloidal droplets. In the present work, the effect of particle size and its distribution on formation of spherical and doughnut shaped hollow microcapsules during rapid evaporation induced self-assembly of colloidal droplets has been elucidated. It has been demonstrated that hollow spherical microcapsules with substantial shell thickness are formed for small size and low polydispersity of the nanoparticles in a virgin dispersion. A few of such microcapsules, even with relatively significant shell thickness, burst in order to equilibrate force balance during drying. In contrast, when the size and polydispersity are relatively high, a morphological transformation occurs and the drying droplets release the strain through formation of doughnut shaped grains. Two levels of structural hierarchy and ageing effects of the assembled microcapsules are investigated using small-angle neutron/X-ray scattering and scanning electron microscopy.