Molecular Dynamics Simulation And Experimental Research Of Solid-liquid Interface Wettibility

With the rapid development of micro/nano electro mechanical systems (MEMS/NEMS), biochips, bionic medical instruments and micro/nano technology in recent years, it is highly urgent to have deep insight into the micro/nano fluidics and the control of the micro/nano wettibility. On the micro/nano scale, because of the large surface-volume ratio, the surface tension constitutes the main interaction between the liquid and the solid surface, which can be, to some extent, indicated by the surface wettibility.Enlightened by the natural "lotus effect", to open out the laws and mechanics of the nano wettibility, molecular dynamics simulation is used to investigate the effect of the surface interaction potential and nano roughness on the wettibility. The simulation result shows that with large interaction potential between the liquid drop and solid surface, the liquid can fully fill in the nano roughness. However, because of the hysteresis, the contact angle isn't distinctively affected. While with small interaction potential, the nano roughness helps to increase the contact angle, even reach up to the superhydrophobic state, by breeding a steamy cushion in the nano clearances.Based on the conclusions above, a hypothesis, that the molecular distribution in the nano channel can be adjusted by the nano roughness of the solid wall and different pressure, is put forward and preparatorily validated by the molecular dynamics simulation. The simulation indicates that in the hydrophilic platinum nano channel, there are three or four distinct argon atom layers at the smooth channel atom wall, while at the rough wall with nano structures, the liquid atoms remain to be stable "crystal lattice structure" and the clearances are fully filled by the liquid atoms and a layer with high density is obtain close the solid roughness surface. With the decreasing of the the channel pressure, it's obviously that the rough wall has a higher interaction force with the liquid atoms than the smooth wall.Experiments are carried out on the silicon substrate to testify the effect of the different interaction potentials and surface roughness on the wettibility. Four conclusions are concluded. Firstly, the surface silanization leads to the reduction of the surface energy and the increase of the contact angle. Secondly, in the hydrophilic state, the contact angle decreases for the existence of the surface micro nano structures. However, because of the hysteresis, little effect is brought by the roughness structure when the roughness factor r is comparatively large. Thirdly, in the hydrophobic state, the existence of the surface micro structures can help to increase the contact angle, even reach up to the superhydrophobic state. Fourthly, in the hydrophobic state, the sliding angle decreases with the increasing of the contact angle.