Size dependent absorption kinetics of sedimenting nanoparticles

Nanoparticles (NPs) beyond a certain size suspended in a lighter fluid medium, fall under gravity after attaining terminal velocity. This velocity is higher for larger particles. Thus absorption kinetics of ZnO NPs reflecting a change in the particle density with time exhibit different slopes for different sizes. A model based on Stoke's law of viscous drag can predict the size distribution of NPs having negligible inter-particle correlations. However, distinct slopes of the absorption kinetics provide a rough idea of the average size of as grown NPs.