The Influence Of Solid Surface Charge On The Interfacial Water

Properties of water at the solid-liquid interface play an important role in the study of wetting,liquid nanotransportation,phase separation,biological membranes,ion channels,etc.A number of experimental and theoretical research studies have provided molecular level insights into the behavior of interfacial water,where within a few molecular dimensions from the surface,the structural and dynamic properties of the interfacial water can be significantly affected by the solid substrate characteristics.We are interesting in that how the solid surface with different charge affects the structural and dynamic properties of the interfacial water.To investigate how the solid surface with different charge affects the structural and dynamic properties of the interfacial water,we used all-atom equilibrium molecular dynamics simulations at ambient temperature.Graphene and magnesium surfaces were considered to assess the structural and dynamic behavior of the first few hydration layers in contact with the substrates.The main researches of this paper include the following two parts:1.The structural behavior of the interfacial water.Density profiles and hydrogen-bond profiles were calculated to assess the structural properties of the interfacial water.Then in-plane radial distribution functions and in-plane density distribution were calculated to assess the structural properties of the first hydration layer.I find that,due to strong substrate-water interactions,the charge pattern of the solid surface provides patterned sites for the formation of an ordered first hydration layer.The positive charged sites attract the oxygen atoms of some water molecules while the negative charged sites attract the hydrogen atoms of some water molecules.With the increase of charge,the water molecules in the first hydration layer become more ordered.2.The dynamic properties of the interfacial water.Residence correlation functions and reorientation autocorrelation functions were calculated to assess the dynamic properties of the first interfacial water.I find that,the residence time of water within the first hydration layer is significantly longer than that obtained from the bulk water layer.With the increase of charge,the residence time of water within the first hydration layer becomes longer.The presence of solid substrate determines anisotropic rotation of interfacial water molecules in the first interfacial layer.With the increase of charge,the rotation rate of water within the first hydration layer becomes slower.It is because that the strong substrate-water interactions and the more hydrogen bonds forming within water molecules in the first hydration layer.