超快激光诱导沟槽表面周期性结构增强毛细扩散性能的研究

Ultrafast Laser-Induced Groove Surface Periodic Structure for Enhanced Capillary Diffusion Properties

针对小尺度沟槽的毛细扩散性能不足问题,利用皮秒激光诱导小尺度沟槽表面周期性结构,通过毛细扩散实验研究了激光诱导沟槽表面不同角度周期性结构对液体流动的影响。结果表明,激光诱导周期性表面结构(LIPSS)改变了沟槽粗糙度,使毛细扩散性能获得提升,并且沟槽中更小的激光诱导周期性表面结构复合角度具有更小的液体流动阻力,从而具备更为优异的毛细扩散性能。在宽50μm、深25μm的沟槽中,具有0°LIPSS的沟槽的毛细扩散性能较光滑沟槽提升了30.8%。

Objective Liquid-transporting functional surface structures play important roles in lithium-ion batteries,heat transfer,and chemical reactions.Grooves are excellent structures for liquid transport and their hydrophilic properties can be improved by generating CuO nanosheets and nanograss structures on their surfaces.However,as the functional surface structure becomes more precise,the mechanism by which the micro-and nanotextures of the surface affect its hydrophilic properties changes.Studies have revealed that micrometer-thick structures such as nanosheets and nanograss within small-scale grooves hinder liquid transport,resulting in a deterioration in liquid transport functions.In addition,the enhancement of the liquid transport performance by reducing the liquid flow resistance has been widely studied.Current efforts to reduce the flow resistance have primarily focused on superhydrophobic surfaces,which are not suitable for hydrophilic application scenarios.Laser-induced periodic surface structures(LIPSSs)are nanoscale structures that form highly periodic,ordered,and directionally controllable patterns,which can enhance the small-scale groove capillary force and drag reduction performance.In this work,the preparation of continuous clear periodic surface structures on a groove surface is realized by studying the effect of different laser parameters on the formation of LIPSSs.Capillary diffusion experiments are carried out on the laser-induced periodic structures on the groove surface.By analyzing the effect of the different composite angles of the LIPSS in the grooves on the capillary diffusion performance,we aim to identify the structures that enhance the liquid transport performance in small-scale grooves and to understand the relationship between LIPSSs and liquid flows.Methods Initially,the formation of copper fragments is suppressed by modulating an ultrafast laser,enabling the creation of smooth V-shaped grooves on the surface of a copper sheet by removing oxides through acid washing after laser ablation.Subsequently,the effects of different laser parameters on the formation of the LIPSSs are investigated to realize the preparation of clear periodic surface structures on the groove surface.Then,surface morphology and geometry are analyzed using scanning electron microscope and laser confocal microscope.The effect of LIPSSs on the liquid flow in grooves with different depth-to-width ratios is investigated via capillary diffusion experiments to evaluate the enhancement effect of LIPSS on the capillary diffusion performance.Additionally,the relationship between the LIPSS composite angle and liquid flow resistance is also investigated using capillary diffusion experiments with grooves featuring different LIPSS angles.In addition,the mechanism behind this action is investigated by analyzing the state of the capillary flow of liquid droplets in the grooves.Results and Discussions LIPSSs are prepared on copper surfaces with a contact angle of 14.7°to enhance the surface hydrophilic properties(Fig.1).An LIPSS prepared with equivalent pulse number(N=160)and energy density(F=0.26 J/cm2)works best(Fig.2).By tuning the laser parameters,clear and intact LIPSSs with different angles can be prepared in grooves with different depthto-width ratios(Figs.3 and 4).The incorporation of an LIPSS in the grooves enhances the capillary diffusion performance,and the effect is more significant in grooves with a small depth-to-width ratio.Smooth grooves with a width and depth of 50μm and 12μm,respectively,do not exhibit diffusion properties,and diffusion occurs only with the addition of an LIPSS(Fig.5).The diffusion properties of the 25μm and 50μm deep grooves with 0°LIPSSs show 30.8%and 29.4%enhancement,respectively,over those of smooth grooves.The compound angle of the LIPSS in the groove affects the flow of liquid.The groove with 0°LIPSS has the best capillary diffusion properties and the groove with 90°LIPSS has the smallest capillary diffusion coefficient(Table 1).Conclusions In this study,we investigate the effect of an ultrafast laser on LIPSSs,resulting in the realization of clear periodic surface structures with different angles within the grooves.The solid surface wettability and capillary diffusion performance can be enhanced by increasing the surface roughness and decreasing the Wenzel contact angle of the LIPSSs within the grooves,and the effect of the LIPSS is more significant in small-scale grooves.Furthermore,the angle between the LIPSS and groove direction affects the flow resistance of the liquid,and structures with a smaller angle between the LIPSS and groove direction exhibit superior capillary diffusion performance owing to small energy barriers and the ability to provide additional capillary forces.In the grooves with a width and depth of 50μm and 12μm,respectively,capillary diffusion occurs only in grooves with 0°LIPSSs.Furthermore,diffusion properties of the 25μm and 50μm deep grooves with 0°LIPSS exhibit 30.8%and 29.4%enhancement,respectively,compared with those of smooth grooves.