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Photo-switching of surface wettability on micropatterned photopolymers for fast transport of water droplets over a long-distance
Polymer Chemistry ( IF 4.6 ) Pub Date : 2020-03-24 , DOI: 10.1039/d0py00263a
E. Rossegger 1, 2, 3 , D. Nees 3, 4, 5 , S. Turisser 1, 2, 3 , S. Radl 1, 2, 3 , T. Griesser 2, 3, 6, 7 , S. Schlögl 1, 2, 3
Affiliation  

The present work addresses the directional movement of water droplets (2 μL droplet) across a photopolymer surface over a distance of more than 20 mm. The long-distance movement of the droplet is achieved by inscribing multi-gradients onto the surface, which is realized by a photo-induced increase in wettability amplified by a change in surface texture. To create highly hydrophobic surface characteristics, photo-reactive resin formulations containing an o-nitrobenzyl alcohol derivative with terminal acrylate groups, a multi-functional thiol and a fluorinated methacrylate monomer are patterned by visible light-assisted nanoimprint lithography. The needle-like surface microstructures in combination with the fluorine groups of the methacrylate monomer enable the formation of photopolymers with static water contact angles in the range of 140°. Subsequent irradiation of the photopolymer with light in the UV-A spectral region leads to the localized formation of polar groups such as carboxylic acids (photolysis of the o-nitrobenzyl ester moieties) and sulfonic acids (photooxidation of free thiol groups). Along with the change in the chemical surface composition, prolonged UV exposure under air erodes the surface microstructures leading to fully wettable surfaces. The controlled photo-switching between highly hydrophobic (140°) and fully wettable (7°) photopolymer surfaces enables the introduction of wettability gradients by asymmetrical UV irradiation. Linear-shaped gradients rapidly drive a water droplet over a distance of 14 mm. By inscribing the wettability gradient in wedge-shaped patterns, a Laplace pressure gradient is additionally formed, which allows a directed movement of water droplets over a distance of 22 mm.

中文翻译:

在微图案化光聚合物上进行表面润湿性的光转换,以实现水滴在长距离上的快速传输

本工作解决了水滴(2μL水滴)在光敏聚合物表面上超过20毫米的方向运动。液滴的长距离运动是通过在表面上刻上多个渐变来实现的,这是通过光诱导的润湿性增加(通过表面纹理的变化而放大)来实现的。为了产生高度疏水的表面特性,含有苯二甲酸酯的光反应性树脂配方通过可见光辅助纳米压印光刻对具有末端丙烯酸酯基团的-硝基苄醇衍生物,多官能硫醇和氟化甲基丙烯酸酯单体进行构图。针状表面微结构与甲基丙烯酸酯单体的氟基团结合使得能够形成静态水接触角在140°范围内的光敏聚合物。随后用UV-A光谱区域的光对光敏聚合物进行辐照会导致极性基团(例如羧酸)的局部形成(邻位的光解-硝基苄基酯部分)和磺酸(游离硫醇基的光氧化)。随着化学表面成分的变化,长时间的紫外线暴露在空气中会腐蚀表面的微观结构,导致表面完全可润湿。在高度疏水性(140°)和完全可湿性(7°)的光敏聚合物表面之间进行受控的光转换,可以通过不对称的紫外线辐射引入润湿性梯度。线性梯度会在14毫米的距离内快速驱动水滴。通过以楔形图案刻出可湿性梯度,可以额外形成拉普拉斯压力梯度,从而允许水滴在22毫米的距离内定向运动。
更新日期:2020-03-24
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