梯度润湿性图案化表面的制备及其输运性能研究

Fabrication of Gradient Wetting Patterned Surface and Its Performance in Transportation

目的针对液体输运距离短、速度慢等问题,提出一种基于梯度疏水基底的箭形图案化表面,该表面能有效改善液滴的输运性能。方法对铝合金表面依次进行预处理、激光加工基底、低表面能改性处理和激光加工箭形亲水图案,得到具有良好输运性能的图案化表面。深入研究激光扫描速度对铝合金表面形貌和润湿性的影响。结果随着激光扫描速度的提高,表面微结构由“微纳分层结构”逐渐变为“亚微米结构”,铝合金表面的粗糙度逐渐变小,导致表面静态接触角由150°左右降至107°左右,动态接触状态由滚动状态变为钉扎状态。另外,随着扫描速度的增加,基底表面O的质量分数从11.2%降至7.7%,F的质量分数从17.6%降至10.6%,表明表面氧化物减少,导致表面对含F有机物的吸附能力减弱,进而导致表面疏水性降低。液滴在基于梯度疏水基底的箭形图案化表面上的输运距离可达到61 mm,相较于均匀疏水基底,提高了34%。结论采用梯度激光扫描速度和低表面能处理可简单、快速地获得梯度疏水基底,相较于基于均匀疏水基底的图案化表面,液滴在基于梯度疏水基底的图案化表面上的输运性能得到显著提高,液滴自发、定向和高性能的输运在水收集装置、传热设备等方面具有广阔的应用前景。

Spontaneous transportation of liquid on wetting pattern has promising applications in water-harvesting devices,heat transfer equipment,etc.However,the technology is limited due to the expensive and complex processing techniques,and weak transportation capacities.An arrow-shaped patterned surface based on a gradient hydrophobic substrate is proposed to address the problems of short transportation distance and slow speed,which can effectively improve liquid transportation performance.Pre-treatment,laser processing substrate,low surface energy modification treatment,and laser processing wetting pattern were sequentially performed on the aluminum alloy surface to obtain a patterned surface with good transportation performance.Firstly,the pretreated aluminum alloy plate was placed on a processed platform,and the gradient hydrophilic substrate was formed by processing the substrate with a grid-like structure and applying laser directly on aluminum alloy surfaces at a gradient scanning speed.Then,the dried processed surface was soaked in fluorinated liquid(FAS-17)for one hour to get low surface energy surfaces.Finally,an arrow-shaped hydrophilic patterned surface was processed on the gradient hydrophobic substrate by laser at a uniform scanning speed for droplet transportation.The processing equipment used in the process was a nanosecond laser with a wavelength of 1064 nm,a pulse width of 200 ns,a maximum power of 20 W and a frequency from 20 kHz to 100 kHz.The effects of laser scanning speed on the microstructures and wettability of the aluminum alloy surface were investigated.The wettability,microstructures,chemical compositions,and droplet transportation performance of patterned surfaces were tested and analyzed with the help of analytical and testing equipment such as a contact angle meter,scanning electron microscope,3D optical profiler,and industrial camera.With the increase of laser scanning speed,the surface microstructure gradually shifted from"micro-and nano-layered structure"to"sub-micron structure",and the roughness of aluminum alloy surfaces gradually became smaller,which led to the decrease of static contact angle from 150°to 107°,and the dynamic contact state of shifting from rolling state to pinned state.In addition,with the increase of scanning speed,the mass fraction of O of surfaces decreased from 11.2%to 7.7%,and the mass fraction of F of surfaces decreased from 17.6%to 10.6%,which indicated the gradual decrease of surface oxide,resulting in the weakening of the adsorption capacity of F-containing organics,and thus the decrease of the hydrophobicity of surfaces.Further,the transportation performance of droplets on gradient wetting arrow-shaped patterned surfaces with different average wetting gradients was investigated,and the result showed that the droplet transportation distance on the arrow-shaped patterned surface based on gradient hydrophobic substrates could reach 61 mm,which was 34%higher than that of the uniform hydrophobic substrate.The gradient scanning speed and low surface energy modification treatment can be used to fabricate gradient hydrophobic substrates easily and quickly.Compared with the arrow-shaped patterned surface based on a uniform hydrophobic substrate,the droplet transportation performance of the arrow-shaped patterned surface based on a gradient hydrophobic substrate is significantly improved.The spontaneous and directional high-performance transportation of droplets has promising applications in water collection devices and heat transfer devices.