Abstract Understanding of the mechanism describing the chemical potential of nanoparticle dispersions, whether from modelling or experimental perspectives, is missing in the literature. As nanofluids are widely used in engineering applications, predicting material properties correctly needs a correct formulation for their behaviour. Often, the chemical potential of mixing is used for such expressions. Although quite appropriate for polymer blends or binary solutions, it is not suitable for nanoparticle dispersions. This work proposes a new mechanism for the chemical potential of dispersions or suspensions from thermodynamic principles, relying on porous flow principles, proposing that it is the fluid that diffuses in between the nanoparticles. The proposed model is applied in the case of mass diffusion and the results compare well with molecular dynamics results and several experimental data, motivating the proposed mechanism for dispersions.