(color online) Diffusion process of the methane in the typical pattern-1 system. Density distributions of the methane gas in the pattern-1 system versus the simulation time. The figure shows the average distributions of the methane gas per ns at the simulation time around 1, 8, 15, and 100 ns. Different color gradients stand for the different densities of the methane gas. The blue color represents the highest density ( 3.2 × 10 − 4 nm − 2 ) of the methane gas around and the white regions stands for the lowest density ( 0 × 10 − 4 nm − 2 ) .