The Molecular Simulation Research On Electrowetting Behavior Of Nano-scale Ionic Liquid Water Droplet

Nowadays,the research of wetting and electrowetting behavior about nano-scale droplets has become an important point in the field of micro-nano fiuidic operation and control,which obtains high attention and have very pervasive practicability in optics,physical chemistry,biology and electrical engineering,and so on.At present,methanol,ethanol,pure water and sodium chloride solution is employed in study of electrowetting behavior about nano-scale droplets,compared with traditional inorganic solution,room temperature ionic liquids(RTILs)show environmentally friendly,healthily safe,high thermosteady and design.RTILs have great potential applications in nano electromechanical system based on liquid and biomedical field.Based on such background,this article studies the wetting and electrowetting behavior of nanoscale room temperature ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate([EMIM][BF4])water droplets on a monolayer graphene surface with molecular dynamics simulation.The research process shows that the contact angles of nanosized water droplets decrease with the increased ionic liquids pairs and the rising temperature without the applied electric field.Through calculating the radial distribution function,we find the forces of ILs-ILs and water-water are stronger than ILswater.Analyzing the distribution of ions in nanosized droplets,we find that ions can interact with the graphene sheet and form a strong absorption layer,leading to a remarkable decrease on equilibrium contact angles with increasing IL pairs and increase of the graphene solid surface wettability.The droplets undergo symmetry-to-asymmetry contact angles deformation until they reach equilibrium with increasing IL pair in same electric field strength and the droplets need shorter time to reach equilibrium state with increasing IL pairs.When applied electric field strength is weaker,the droplets present an asymmetric deformation process;and when the electric field is stronger,the droplets emerge symmetrical deformation to reach equilibrium.The research results show that the electric field strengths and the increase of cation-anion ion pairs can improve the wetting behavior of nano-sized water droplets,and reveal interaction mechanism of ionic liquids and water droplets,which can provide theoretical basis for the electronwetting in bio-molecular sensing in electromechanical systems.