The influence of particle clustering on the rheological properties of highly concentrated magnetic nanofluids

► The highest solid volume fraction of the magnetite nanoparticles was 21%. ► DLS and magnetogranulometry revealed weak particle clustering. ► Viscosity versus solid particle concentration was fitted with Krieger-Dougherty formula. ► 1.3 part./cluster and 1.4 nm surfactant layer thickness were estimated from the fit.