Granular materials consisting of macroscopic grains have commercial applications and their flow behavior plays key role in geophysics. However, flow characteristics of nanogranules differ significantly from those of granules. The former can form low-volume fraction (5%) particle gels in air and do not exhibit gravity-driven granular flow easily. It is found that although dry nanogranules possess a high compressibility, close to gases, they are less susceptible to flow than granules due to high yield stress and viscosity. Such differences can be attributed to van der Waals attractions, which support the weight of nanoparticles to form aerogels and resist shearing deformation. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3575575]
