We use direct imaging and dynamic light scattering to reveal the previously unknown dynamic self-assembly of detonation nanodiamond dispersions in water which have been purified without additional surface modification.

The discovery of the multipolar surface electrostatic potential on faceted diamond nanoparticles explained numerous observations over the past decades, but also raised questions as to how it could be reconciled with seemingly contradictory observations of micron sized diamond and bulk diamond surfaces. It was also unclear how surface electrostatic potential would vary for more quasi-spherical shapes, and derivatives of the ideal truncated octahedron. Here we present new results examining the size-dependence of the multi-polar surface electrostatic potential up to experimentally relevant sizes, and explore the impact of {110} facets which have been shown to present in reasonable quantities (experimentally). We have used computational methods that are consistent with previous work to allow for a direct comparison, and show that both particle size and the fraction of {110} facets on nanodiamond play a critical role in the surface charge. When the particle size is below ∼2.5 nm multipoles are likely to dominate, but over ∼3.0 nm the {110} facets efficiently neutralize the charges leading to a practically monopolar distribution, consistent with observations at other length scales.