Study On The Wettability Of Water Droplet At The Wetting Gradient And Heterogeneous Surface

The wetting and motion of droplet are natural phenomenons,which have widely applied in biochips,condensation heat transfer and inkjet printing et al.As the development of nanotechnology,the wetting and motion of nanodroplet exhibit a promising application prospect.However,the study on the wetting of nanodroplet was scare,especially on the wetting of wetting gradient and heterogeneous surfaces,and the wetting mechanism was still explicit.Due to the size effect,the wetting behavior had essential difference between macroscopical and microscopic droplet.Therefore,it is necessary to develop the fundamental research for the droplet wetting of wetting gradient and heterogeneous surfaces.Hence,in this work,molecular dynamics simulation was employed to study the wetting and motion behavior of water droplet and the mechanisms were investigated as well.When the water nanodroplet was put onto the wetting gradient surface,it could spontaneously move from the hydrophobic segment to the hydrophilic segment.Detailed observation revealed that the motion of nanodroplet included spreading and shrinking processes,and a precursor film forming on the-NH₂ segment played a pivotal role on the transportation of nanodroplet.The microscopic motion mechanism was discussed,and the intricate and intriguing effects of Ebind and Ewater were analyzed to unveil the driving and resisting forces.Furthermore,the modified segment width and wetting gradient were also discussed,and the results unraveled that the narrow modified segment and large wetting gradient promoted the motion of the nanodroplet.The study on the wetting behavior of water nanodroplet on the heterogeneous surface indicates that with the increase of water droplet size,four different adsorption processes possessing distinct characteristics,i.e.spreading,restricting,vibrating and slipping,are presented.The detailed adsorption processes and some microscopic parameters including contact angle,density distribution profile,interaction energy,etc.are proposed to unveil the wetting mechanism.Our research indicates that the strong restriction originated from hydrophilic patch plays a pivotal role in the adsorption process when the size of water droplet is small（R<19?）.As the water droplet is large enough（R≥19?）,the influence of hydrophilic patch is largely weakened,and the wetting behavior is dominated by the hydrophobic surface.