Anisotropy diffusion of water nanodroplets on phosphorene: Effects of pre-compressive deformation and temperature

Abstract

Diffusion of water across surfaces generally involves motion on an uneven and vibrating but otherwise stationary substrate. Based on molecular dynamics simulations, we study the diffusion behavior of water nanodroplets on the compressed phosphorene at different temperatures. The compression is applied in three different ways: equal biaxial compression, uniaxial compression along armchair and zigzag directions As the compressive strain increases, the diffusion coefficients are first reduced and then increased in all three cases at T=300 K. When the compressive strain exceeds 1.6%, the diffusion coefficient grows the fastest for the case of equal biaxial compression. As the temperature increases, two different modes are observed at the lower strain level (⩽1.4%) and relatively higher strain level (⩾1.4%). In the regime of lower level of strain, the diffusion coefficient exhibits an oscillating trend as the temperature increases. In the regime of higher level of strain, the diffusion coefficient increases linearly as the temperature increases. The fastest diffusion occurs under the equal biaxial compressive loading at the strain level of 2.4% and temperature T=340 K. The different diffusion behaviors of water nanodroplets are found to be related to the surface morphologies of phosphorene under compression, as well as friction coefficient and diffusion energy barrier of water molecules. Our results show that compressive deformation of phosphorene and temperature are important to control the dynamics of water molecules on the phosphorene. The phenomena reported here enrich the knowledge of molecular mechanisms for nanofluidic systems, and may inspire more applications with phosphorene and other 2D materials.