Molecular Dynamics Simulation On Wettability Of A Liquid Droplet On Nano-rough Surface

In nature,implanting micro-nano structures on the solid surface can achieve significant hydrophobic properties,such as lotus leaf with micro/nano-level protrusions.With the rapid development of micro-nano technology,studying wettability of a liquid droplet confined in nanoscale rough substrates has important guiding significance for the design and regulation of intelligent superhydrophobic materials.Therefore,designing specific nano-rough surfaces to obtain significant hydrophobicity has become a research hotspot.However,a large number of researches mainly focus on rectangular nano-rough surface,while the new phenomenon,new law and new mechanism caused by wettability of nanostructured rough surfaces are still not well revealed.This article aims to obtain nanostructured rough surfaces with better hydrophobicity,and conducts research on wettability of droplet on nanostructured rough surfaces with different geometric morphologies.The main research contents and conclusions are showed in follows:Taking wettability of nanostructured rough surfaces with different shapes as an entry point,molecular dynamics simulation is used to study wettability of a liquid droplet on five different nano-rough surfaces.The result shows that inverted triangular nanostructure has the best hydrophobicity.Compared with the number of liquid atoms penetrating into the groove for inverted triangular nanostructure,it is twice for trapezoidal or rectangular nanostructure,and thrice for concave lens hyperboloid or triangular nanostructure.It can be seen that hydrophobicity of the nano-rough surface will be increased as the center of gravity of the nanostructure moves upward.Based on this,on the one hand,wettability of a liquid droplet on nanoscale inverted triangular nanostructure was examined with particular emphasis on the effect of different height and interval of the inverted triangles.It is found that increasing height of inverted triangular nanostructures or decreasing interval,hydrophobicity of liquid droplet gradually increases.However,there is a critical value for the influence of height on wettability of liquid droplet.When height increases to the critical value,increasing such height continuously can no change wettability of inverted triangular nanostructures.Such critical value will become smaller with interval decreasing.On the other hand,wettability of a droplet on solid surface with nanoscale inverted triangular grooves was studied under the different energy parameters by molecular dynamics simulations,which can be characterized by penetrating rate.It is found that penetrating rate can be divided into four different subregions with increase energy parameters,which increases firstly and then decreases lately.In the wetting states space,the large energy parameter makes droplet gradually transit from the hydrophobic Cassie state to the hydrophilic Wenzel state.When energy parameter exceeds the critical value(～7),wettability reverses,where atom movement and spatial distribution of droplet molecules shows obvious regularity.Liquid atoms undergo significant solid-liquid interactions in the five layers space near solid-liquid interface.Especially,droplet atoms in the first layer near the solid surface are more evenly distributed at the center of the lattice line or crystal plane,which approximates epitaxial growth of solid atoms to hinder droplet penetrates into the groove.Moreover,with a large energy parameter,movement of liquid atom is weak,which reflectes in its narrow movement area,short and relatively smooth trajectory.While droplet with weak solid-liquid interaction shows a long tortuous movement trajectory,strong movement ability,and wide movement range.In this paper,wettability of nanostructure with different shapes was studied,and an inverted triangular nanorough surface with better hydrophobicity was obtained.In addition,studying the influence of nanostructures with different heights,interval and energy parameters on wettability can explore hydrophobic mechanism of inverted triangular nano-rough surface.The result provides a theoretical basis for the design and improvement of intelligent artificial superhydrophobic surfaces.