Search

A combination of grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations (GCMD simulations) was performed to investigate the effect of the difference in chemical potential between the pore surface and gas phase on the adsorption and desorption kinetics of water in a hydrophilic mesopore. The chemical potential of water vapour was controlled by the GCMC method and the adsorption/desorption of water to/from a hydrophilic mesopore was simulated by the MD method. The calculation results showed that when the stepwise change in chemical potential of the gas phase was small, the initial rate of adsorption or desorption of water could be well predicted by the kinetic theory of gases. However, the rate greatly varied depending on the transport mechanisms of water in mesopores such as film flow and column flow. On the other hand, when the stepwise change in chemical potential was large, the initial rate was overestimated by the kinetic theory of gases; however, it did not change greatly w...

Non-equilibrium molecular dynamics (MD) simulations were performed to investigate the capillary evaporation of water confined in hydrophilic mesopores. The electrostatics-based (ELBA) coarse-grained water model was employed to calculate the duration of the time-consuming capillary evaporation process. To evaluate the effect of hydrophilicity of mesopores on the capillary evaporation of water, three types of thin films with a cylindrical mesopore were modelled by tuning the interactions between water and wall atoms. Initially, the cylindrical mesopore was filled with water, and evaporation of the water into vacuum was simulated. The calculation results showed that when capillary evaporation occurred, the desorption rate of water was almost constant in a highly hydrophilic mesopore where a stable water layer was formed on the pore surface, whereas the rate decreased with time in a weakly hydrophilic mesopore where the water layer did not remain stable. As time progressed, the water column shortened ...

Molecular dynamics simulations of three types of normal alcohols (n-alcohols), n-propanol (C 3 H 7 OH), n-heptanol (C 7 H 1 5 OH), and n-undecanol (C 1 1 H 2 3 OH), adsorbed on water, were carried out as a function of the n-alcohol concentration. The simulation results reveal the following. The distribution of n-propanol on water is homogeneous at all concentrations studied here, and the distribution of n-heptanol and n-undecanol on water is heterogeneous. For n-heptanol, the steady adsorption layer appears discretely as the number of n-heptanol increases. When a monolayer or multilayer of n-heptanol is formed on water, the fluctuations of the water surface are small. But large fluctuations can be observed between these two concentrations. For n-undecanol, the n-undecanol molecules tend to cluster in a single region on the water surface below the concentration at which the monolayer of n-undecanol is formed These molecular dynamics simulations indicate the generation of fluctuations in the alcohol distribution on water that lead to heterogeneous distribution.

In order to investigate the dynamic process of the absorption of water vapor into aqueous electrolyte solution, molecular dynamics simulations were carried out under nonequilibrium conditions. The two boxes at liquid-vapor equilibrium at different saturation pressure are coupled. One box contains water and the other box contains aqueous electrolyte solution. The variables are the temperature of the water, the temperature and concentration of the aqueous electrolyte solution, and the pressure difference between the two boxes. The absorption rate was calculated and some molecular pictures are reported. On the molecular scale, ions are negatively adsorbed at the surface, particularly in weak aqueous electrolyte solution, and highly concentrated aqueous electrolyte solution is effectively ''frozen'' and cannot rapidly adjust to the incident water vapor molecules. These structural and dynamical properties affect the absorption rate.