The spreading of graphene oxide suspensions droplets on smooth surfaces

The impact of Newtonian fluid droplets on a solid surface has been extensively studied but much remains to be understood when the fluid is non-Newtonian. Here, we study experimentally and theoretically the spreading behavior of graphene oxide suspension droplets impacting on a smooth surface for a wide range of concentrations and impact velocities. Graphene oxide suspensions are shear thinning and exhibit yield stress behavior at higher concentrations. The rheology for all concentrations is well described by a Herschel-Bulkley model that allows us to determine the characteristic viscosity during spreading. We use this viscosity to develop an energy balance model that takes into account the viscous dissipation and change in surface energies to find the maximum spread diameter for a given impact velocity. Our model agrees well with our data for a wide range of concentrations – from the viscous to the yield stress regime.