Molecular dynamics simulation on spreading of mixture nanodroplets on a smooth and homogeneous surface

The dynamic wetting of mixture droplets on the solid surface is important for various industrial technologies and applications, such as evaporation, microfluidics, surface self-cleaning, and power cycling. Due to the influence of different components, the dynamic wetting process of mixture droplets is quite different from that of pure fluids. Currently, the understanding of the spreading mechanism of mixture droplets is lacking. In this paper, molecular dynamics simulation is used to study the dynamic spreading process of ethanol/water and difluoromethane (R32)/2,3,3,3-tetrafluoroprop-1-ene (R1234yf) mixture droplets on a smooth and homogeneous surface. The droplets have different component mole fractions and various diameters of 9.4–12.8 nm. The influences of the component mole fraction on the spreading radius and dynamic contact angle are analyzed and compared with molecular kinetic theory. It is found that for the R32/R1234yf mixture droplets, the component mole fractions in the bulk and at the interface of the droplet are close and the dynamic spreading process is similar to that of pure fluids. However, for the ethanol/water mixture droplets, the mole fraction of ethanol is higher at the vapor–liquid and solid–liquid interfaces than in the bulk, and the spreading is faster than that of pure fluids. The mole fraction and the physical properties in the triple contact region are analyzed, and an improved prediction is proposed for the moving velocity of the triple contact line and the spreading process of the mixture droplet.