Molecular Dynamics Simulations Of The Growth Mechanism Of Methane Hydrate And The Wettability Of Graphene Surface

With the development of the science and technology and the popularization of the computers, molecular simulation is applied in science widelier and widelier. The experience process can be simulated precisely using the molecular simulation and this method can create accurate forecasts and replenishment of the experience results. In this paper, molecular dynamics simulation is applied to study the growth of the methane hydrate and the wettability of the graphene surface, and a series of theoretical calculations are made about the topics. The paper concludes two main parts: one is the molecular dynamics simulation of the methane hydrate growth and the other is the molecular dynamics simulation of the wettability of the graphene surface.In the part one, molecular dynamics simulation is used to study the growth mechanism of methane hydrate. In the simulations, two factors are taken into consideration. One is the methane concentration and the other is the presence of ions. Five initial configurations are created with different methane concentrations in the liquid phase. The well-known OPLS-AA and TIP4P-EW models are used for CH4 and H2 O, respectively. And the interaction between H2 O and CH4 is described with the Lennard-Jones 12-6. In an attempt to obtain reasonable results, the growth simulations are performed at four different pressures(15.0, 25.0, 35.0, 45.0 MPa) blow the critical temperature 276.0K, respectively, for each model. In the progress, the solid-liquid interface plays an important role. We use the angular order parameter as an index for identifying the location of the interface. Then we can know the time evolution of the hydrate thickness. Our results indicate that the growth rate will be the largest when the methane concentration is close to the methane concentration of the s I hydrate. Also we investigate the effect to the growth with some ions in the systems. When we add Na+, Mg2+ and Cl- in the liquid phase, the growth rate decreases significantly. That is to say the presence of the ions has an inhibition effect on the hydrate growth. The simulations are of great significance in the application of a new energy source.In the second part, the wetting behavior of water near a graphene sheet is investigated by means of molecular dynamics simulations. In the simulations, the C-C bond length of the graphene changes in a certain range. We should observe the change of the contact angle. The initial models conclude a graphene sheet with different C-C bond length and water molecules. The water molecules use the TIP4P-EW model and Lennard-Jones 12-6 is used to describe the interaction of C and O. In the simulations, the graphene sheet is fixed to simplify calculations and increase the efficiency. The trajectories are analysed to obtain some important information. First we calculate the density distribution of the water when the system is in equilibrium. Then the water droplet profile is clear and the contact angle can be calculated. With the increase of the C-C bond length, the wettability of the graphene decreases. As a typical model in studying the wettability of solid surface, the system is of great sense to explore the surface chemistry. The density distribution, the droplet profile and the measurement of the contact angle are the basic information to study the wettability of liquid on the solid surface.