A Case Study On Evaporation Characteristics Of Multi-Component Droplets On Micropatterned Surface

Droplet evaporation technology is widely used in many fields,such as spray cooling,DNA chip fabrication,inkjet printing,electronic device cooling.Evaporation of multi-component droplets is more practical and common in industry and life than single-component droplets,while having a more complex evaporation mechanism.At present,most studies on the evaporation behavior of multi-component droplets focus on uniform wettability surfaces,and less on non-uniform wettability surfaces.Therefore,the micropatterned non-uniform wettability surface was prepared and the effect of the surface on the evaporation behavior of multi-component droplets was studied,and the influence of various factors on the evaporation process of multi-component droplets was analyzed.First,a micro-patterned surface is prepared on the surface of the titanium sheet in combination with anodization and ultraviolet lithography to achieve any wettability and patterning of the surface of the titanium sheet.The contact angle in the hydrophobic region is up to 165°;the contact angle in the hydrophilic region is below 10°.Second,comparing the evaporation behavior of multi-component droplets and pure water droplets on the uniform wettability surface,both evaporation processes include the constant contact area stage(CCR stage)and the mixed evaporation stage.The addition of ethanol reduces the pinning effect of the solid surface on the droplets.At the same time,the multi-component droplets have evaporation priority during the evaporation process,and the high-volatility ethanol component preferentially evaporates in the early stage of evaporation,and the multi-component droplets approach the pure water droplets in the late stage of evaporation.The micro-patterned surface can control the distribution of multi-component droplets on the surface,so that the three-phase contact line of the droplet is pinned at the boundary of the hydrophilic island,prolonging the length of the three-phase contact line and the pinning time,and the evaporation time is more uniform.The surface is reduced by 25.6%.In the mixed evaporation stage,the characteristic parameters of the multi-component droplets are no longer a smooth change,but exhibit a jump-stick slip evaporation mode.Finally,we explored the effects of ethanol component concentration,substrate temperature,hydrophobicity ratio and surface pattern on the evaporation behavior of multi-component droplets.Increasing the concentration of the ethanol component can significantly shorten the evaporation process of the ethanol component,reducing the evaporation time by 25.3%.At the same time,as the concentration of ethanol increases,the proportion of evaporation time in the CCR phase gradually decreases.When the substrate temperature was increased by 15 ° C(from 30 ° C to 45 ° C),the total evaporation time of the multi-component droplets was shortened by 69.2%.Increasing the substrate temperature can accelerate the evaporation process of the ethanol component,so that the multi-component droplets change from water-ethanol droplets to pure water droplets faster;prolong the CCR phase time of the droplets,thereby increasing the evaporation rate of the droplets.Compared to the surface with a 1:3 ratio of hydrophilic to hydrophobic,the evaporation time of the multi-component droplets on the 2:1 surface of the hydrophilic-hydrophobic ratio was shortened by 41.4%.Increasing the hydrophilic ratio can prolong the CCR evaporation phase of the droplets,and the droplet splitting phenomenon occurs after the jump,so that a small amount of liquid remains on the hydrophilic island,and the evaporation rate of the multi-component droplets is improved.The multi-component droplets have an asymmetric evaporation behavior on the striped micropatterned surface,i.e.,the droplet contact lines preferentially shrink in the stripe parallel direction.When the aspect ratio of the multi-component droplets is less than 1,the droplet contact line begins to jump in the vertical direction of the stripe.Appropriately increasing the aspect ratio of the multicomponent droplets on the micropatterned surface can facilitate the evaporation process of the droplets.