Cluster-cluster interaction in nanodiamond hydrosols by small-angle scattering

•The structure and interaction of branched nanodiamond clusters in water were studied by combined X-ray and neutron small-angle scattering.•Special analysis of small-angle scattering by interacting fractal clusters is developed.•The cluster number density together with the content of non-aggregated particles was determined.•The effective pair potential of cluster–cluster interaction close to hard-sphere type is obtained.•Effective correlation length decreases with increasing concentration.