Evolution of shape isotropy in silica microparticles induced by the base

Evolution of shape isotropy in silica microparticles synthesized by sol-gel method is examined by varying the concentration of ammonia. The morphology evolved from worm-like structure to monodisperse spheres. The shape evolution is attributed to the “Pearl-necklace” mechanism wherein the worm-like silica particles due to constrain in its mobility, collapse to an energetically favored spherical morphology with intermediate doll/frustum cone-like morphologies. Plausible reason for the collapse in morphology could be the conformational entropy of the worm-like particles to explore various re-arranged morphologies arising due to Rayleigh-Plateau instability. The collapse in morphology is analogous to the coil to globule transition in polymeric systems; however, the length scales explored in the present study are of the order of micrometers, and the collapse depends on the base concentration. The present system will serve as a model for understanding the various re-arrangements undergoing during the compaction of biological moieties.