Research Of Measurement Methods For Surface Wetting Of Materials

The wettability of material surfaces has promising potential applications in engineering,contact angle has gained great attention in recent research as an intuitionistic characteristic of wettability.Up-to-now,it remains disputation at methodology of contact angle measurement.Composite materials can achieve efficient application of material property,and the characteristics of their surface wettability have become another research hotspot.In this work,the contour method(both 2D&3D models)and the height method for contact angle measurement are systematically studied and compared using molecular dynamics simulations.Moreover,the wettability characteristics of two simple composite materials are studied.The research not only plays a critical role in molecular dynamics simulation and ab initio molecular dynamics of wettability,but also provides theoretical guideline for studying the surface wettability of complicated composite materials.The results are summarized as follow:(1)Firstly,the contact angles of different sizes droplets on different wettability surfaces are studied,the results show that the three-dimensional models obtain the macroscopic contact angle according to the linear relationship of cos??1/R_B,and the contact angle of the two-dimensional models converge rapidly with the increase of the simulation system.The intrinsic wetting angles predicted from the 2D and 3D simulation models are slightly different and the discrepancy is less than 8 degrees,therefore both the two models can be applied to predict contact angle.It takes longer for the droplets to reach equilibrium on the hydrophilic surface than on the hydrophobic surface.The equilibrium time of the system increases with the increase of the droplet size,and the changes in equilibrium time relative to droplet size become more significant when the material is more hydrophilic.(2)The least droplet in wettability is defined in molecular dynamics simulation in accordance with the relationship of cos??1/R_B.Moreover,the height method is optimized with the analysis of droplet partition and the correction volume of droplets hence the height of the droplet becomes the only required variate.(3)The wettability characteristics of the composite material surface are studied.The wettability of the material surface is controlled according to change the proportion of superhydrophobic materials in the composite material.The contact angle increases with the increase of the proportion of superhydrophobic materials.Furthermore,the contact angles obtained by simulation are in good agreement with the theoretical calculation,and the relative error is less than 6%;There is a pinning effect in the process of wetting on the surface of the composite materials.It is found that the non-equilibrium interaction of the solid-liquid-vapor three-phase contact line region is the source of the pinning force on the contact line.The pinning effect is the cause of the mutation in the contact angle.The property of the solid-liquid-vapor three-phase contact line region is the main factor affecting the contact angle.