Molecular Dynamics Simulation Of Wetting And Electrowetting Of Ionic Liquids On Solid Walls

Ionic liquids are widely used in micro-electronic fields such as micro-zoom lenses,liquid microscopes,and supercapacitors because of their good electrical conductivity,designability,and non-volatile properties.Compared with traditional solutions,exploring the wetting behavior of ionic liquids is of great significance for the development of new energy storage materials at the nanoscale.In this paper,the molecular dynamics simulation method was used to study the wetting and electrowetting properties of nano-ionic liquid droplets on solid walls.The ionic liquid selected a classical disubstituted imidazole type ionic liquid-1-butyl-3-methyl-imidazole tetra Fluoroborate[BMIM][BF₄],and the coarse-grained method is used to simplify the all-atom model to speed up the calculation speed while ensuring the accuracy,and the walls are selected from typical silicon and graphene walls.The electrowetting characteristics of ionic liquid droplets were studied by applying an external electric field.The contact angle,particle number density and orientation distribution were analyzed to characterize the wetting process.Influence of wetting characteristics.The main research contents are as follows:First,the wetting model of ionic liquid droplets on the silicon wall is established,and the wetting behavior of droplets on the lyophilic wall with different energy parameters is studied.It is found that the contact angle of the ionic liquid in the equilibrium state on the solid wall gradually decreases as the wall transitions from lyophobic（ε=0.1kcal/mol）to lyophilic（ε=3.0kcal/mol）.And by changing the temperature of the system,it is found that the temperature change has a greater effect on the wetting of the lyophilic wall by the ionic liquid.After the free wetting equilibrium,positive and negative strong and weak electric fields（E=±0.08,±0.18 V/?）in the vertical direction were applied to the system to simulate the electrowetting properties of ionic liquids under different electric field parameters.By studying the number density distribution curve,particle orientation distribution curve and other parameters in the first wetting layer near the wall,the phenomenon of asymmetric wetting contact angle of ionic liquids under the action of positive and negative electric fields is explained.Then,in the wetting model of the wetting of graphene sheets by aqueous ionic liquids,the effects of different amounts of water molecules on the wetting contact angle of aqueous ionic liquids were explored.It is found that in the process of free wetting of mixed droplets,water molecules mainly play a role in reducing the viscosity.With the increase of the number of water molecules,the contact angle of mixed droplets for free wetting between flat graphene plates increases.After the free wetting equilibrium,a vertical and plate-up electric field（E=0.05,0.1,0.15,0.18,0.2 V/?）was applied to the whole system to simulate the electrowetting behavior of the aqueous ionic liquid along the upper and lower plates under different electric field intensities.By analyzing the number density distribution curve of the ionic liquid along the vertical wall direction,the change of the contact angle and other parameters,the reasons for the partial layer phenomenon in the mixed droplet were explained and the corresponding conclusions were obtained,which provided theoretical guidance for the subsequent experimental simulation.