Micro-Patterning Of Titanium Surface And Its Effect On Droplet Evaporation

The dynamic and thermodynamic behaviors of Micro-droplets in the solid surface are commonly used in microelectronics cooling,anti-fog,dust prevention,anti-frost and other fields.In recent years,Microelectronics products and micro-execution devices have developed rapidly.It is generally believed that the microscopic characteristics of the materials' surface have a decisive effect on the thermodynamic behavior of droplets.However,the research is primarily focused on the surface of homogeneous or regular structure,the study of micropatterned wettability surface is rarely reported in the literature.Therefore,in this paper,we prepare the superhydrophobic/hydrophilic pattern surface,study its effect on the evaporation behavior of the single droplet and the evaporation rate of the dispersed droplets.(1)Preparing the patterned surface.Firstly,TiO2 nanotubes are made on the surface of pure titanium sheet by anodic oxidation method.The nanotubes let the surface have a nanoscale roughness.Then,the surface is annealed to transform amorphous TiO2 into anatase phase TiO2 with photocatalytic activity.Finally,after hydrophobic treatment of the surface with FAS-17,ultraviolet light is used to irradiate the titanium sheet under a mask.The titanium sheet surface forms a superhydrophobic/hydrophilic pattern.On the surface,the contact angle of hydrophobic parts is up to 171°,the contact angle of hydrophilic parts is under 10°.The surface owns a good ability of controling the droplet distribution to form a clear pattern of water.(2)Studying the effect of grid-like superhydrophobic/hydrophilic pattern on the evaporation behavior of single droplet.We discover that the droplet evaporation process is divided into two stages,the CCR mode evaporation stage and the Stick-Jump mode evaporation stage.CCR mode appears in the early stages of evaporation when the solid-liquid contact surface diameter is almost constant,contact angle and liquid height decrease linearly.The StickJump mode appears at the later stage of evaporation.At this time,the three-phase contact line jumps and shrinks,resulting in a stepwise decrease in the diameter of the solid-liquid contact surface and the leapingly decrease in liquid height and the contact angle.Between two adjacent jumps,the droplets evaporate in CCR mode.(3)Studying the effect of hydrophilic dot array pattern and hydrophilic square array pattern on the evaporation rate of dispersed droplets.The natural evaporation and forced convection evaporation of the droplets are observed on the two surfaces with the pure hydrophilic surface as reference.Whether it is natural convection or forced convection,the two patterned surfaces can both promote the evaporation rate in the early stages of droplet evaporation.In contrast to the natural evaporation,forced convection can amplify the effect on promoting droplets evaporation.For example,in the first 15 min of the evaporation,the promotion effect increase from 8.8 %(natural)to 14.9 %(forced convection)on the hydrophilic square array pattern surface,the promotion effect increase from 6.8 %(natural)to 15.5 %(forced convection)on the hydrophilic dot array pattern surface.However,since the droplet evaporation rate on the patterned surface decreases faster than on the hydrophilic surface,the droplet on hydrophilic surface evaporates faster than on the patterned surface in the later stage.It results in that the promotion of the two patterned surfaces for droplet evaporation is not obvious at the total evaporation time.The above results show that the surface with the superhydrophobic/hydrophilic pattern has a good control of the distribution of the liquid,which can influence the evaporation behavior of single droplets and the evaporation rate of the dispersion droplets on the surface in a nonstructural manner.This expands the type of surface,and makes the application of the sessile droplets evaporation more diverse.