Nanofluids are colloidal suspensions of nanoparticles (1-100nm). The nanoparticles are typically suspended in water or organic liquids. Nanofluids tend to behave differently than simple fluids in many ways. For example, Wasan and Nikolov show experimentally how the spreading coefficient of nanofluids is dependent on the thickness of the film, unlike in simple fluids. Besides spreading dynamics, nanofluids can have various unique properties such as greatly enhanced energy transfer and reduced tendency for sedimentation and erosion of contained surfaces.
Wasan, D.T., Nikolov, A.D., Nature 423 (2003) http://web.mit.edu/nse/nanofluids/