Molecular dynamics simulation of the surface tension and contact angle of argon and water

Surface tension and contact angle have been studied actively for decades because of their extensive and significant physical importance in various fields of technology and engineering. However, because of the complexity of the solid vapor, solid/liquid and liquid/vapor interfaces, there still is difficulty in accurately predicting the surface tension and contact angle. The present dissertation focuses on molecular dynamics investigations of surface tension acid contact angle of argon and water. According to this work, some methods for predicting surface tension and contact angle have been suggested. The results can he summarized into the following aspects.; With the PPPM method, we studied the density and surface tension of argon and water. For the argon case, it shows that the density and surface tension match the experimental data quite well. For the water case, it is found that at high temperatures (near critical temperature), the density and surface tension diverge from experimental data. It is also shown that by using the PPPM method, the cost of calculation is reduced dramatically while the accuracy is improved for the calculation of water.; A fluid layer attached to a solid wall has also been studied by molecular dynamics simulation. It shows that the thickness of fluid film has to be more than 2nm to achieve the accurate results. It is found that the density of fluid near the solid wall fluctuated greatly and that the structure is more like a solid than a fluid. This may explain the high thermal conductivity of nano-fluids. Also, the surface tensors in the interface of liquid/vapor, liquid/solid and vapor/solid are evaluated in the simulation. They are used to verify the Young's equation.; Argon and water droplets are simulated adjacent to a solid surface using molecular dynamics. It is concluded that the contract angle decreases for increasing system temperatures and increases when the potential decreases. When the temperature is high enough, the contact angles drops to zero. The results were compared with the argon-virtual solid wall and water-aluminum, a similar trend was found.; Based on the surface tensors in the interfaces calculated in Chapter 4, contact angles are calculated by using Young's equation. It is found that the values fit the direct simulation results (Chapter 5) very well. The validation of Young's equation at the nanometer scale is shown.; Contact angle of a moving Lennard-Jones fluid and water droplets on a stationary solid surface is studied as well. It is shown that the advancing contact angle increases and the receding contract angle decreases with increasing droplet velocity.