Reversible switching between superhydrophilicity and superhydrophobicity
Reversible switching between superhydrophilicity and superhydrophobicity
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DOI：
10.1002/anie.200352565
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
Zhu, DB
中科院分区：
文献类型：
--
作者：
Sun, TL;Wang, GJ;Zhu, DB
润湿性是一个非常重要的性质，它受化学成分和表面结构的影响。[1-9]近年来，表面润湿性的控制因其广泛的应用而引起人们极大的兴趣。通常，水接触角（CA）大于1508的超疏水表面[1-6]可以通过控制疏水表面的形貌来获得，而CA约为08的超亲水表面可以通过亲水表面上的3D [7-8]或2D毛细效应[9]来实现。刺激响应表面[10]可以可逆地控制表面的润湿性，并已通过各种方法证明，包括光照射[11，12]电场的使用[13，14]热处理[15]和溶剂处理。[16]然而，超亲水性和超疏水性之间的可逆切换从未报道过。在这里，我们显示了粗糙度增强的聚（N-异丙基丙烯酰胺）（PNIPAAm）改性表面的热响应润湿性。[17超亲水性和超疏水性之间的可逆切换可以在约108 ℃的窄温度范围内实现，这被认为是由表面的化学变化和表面粗糙度的组合效应引起的。这种可切换表面可以在功能性纺织品、智能微流体切换、可控药物释放和热响应过滤器中具有广泛的应用。使用表面引发的原子转移自由基聚合[19，20]在平坦和粗糙的硅基底上制造热响应PNI-PAAm薄膜[21-24]。原子力显微镜（AFM）和扫描电子显微镜（SEM）的结果表明，PNIPAAm薄膜的厚度可以很好地控制的聚合时间。图la（左）示出了已经用PNIPAAm薄膜改性的粗糙基底的典型SEM图像。与平坦基底的光滑表面（图1a右侧）相比，粗糙基底呈现出规则的正方形硅微凸体阵列（明亮的正方形）。暗线是宽约6 μm、深约5 μm的微槽。这些微槽通过激光切割机（参见实验部分）在硅晶片上在约11 cm 2的区域中产生。表面粗糙度可以通过控制凹槽之间的间距来调节。在我们的实验中，选择了约31 μm，18 μm，8 μm和6 μm的不同槽间距。粗糙表面的放大图像显示，微凸和微槽也相当粗糙（图1b）。在PNIPAAm聚合之前（图1c）和之后（图1d）的硅微凸体的进一步放大的SEM图像显示，这些微凸体在PNIPAAm聚合之前（图1c）和之后（图1d）的硅微凸体在PNIPAAm聚合之前（图1c）和之后（图1d）的硅微凸体在PNIPAAm聚合之后（图1c）和之后（图1d）的硅微凸体在PNIPAAm聚合之前（图1c）和之后的硅微凸体在PNIPAAm聚合之后的硅微凸体在PNIPAAm聚合之前（图1d）的硅微凸体在PNIPAAm聚合之后的硅微凸体在PNIPAAm聚合之前和之后的硅微凸体在PNIPAAm聚合之后的硅微凸体在PNIPAAm聚合之后的硅微凸体在PNIPAAm聚合之后的硅微凸体在PNIPAAm聚合之前和之后的硅微凸体在PNIPAAm聚合之前。
Wettability is a very important property that is governed by both chemical composition and surface structure.[1–9] Recently, the control of surface wettability has aroused great interest because of its wide variety of applications. In general, superhydrophobic surfaces [1–6] with a water contact angle (CA) greater than 1508 can be obtained by controlling the topography of hydrophobic surfaces, while superhydrophilic surfaces with a CA about 08 can be realized through a 3D [7–8] or 2D capillary effect [9] on hydrophilic surfaces. Stimuli-responsive surfaces [10] make it possible to reversibly control the wettability of the surface and has been demonstrated by various methods, including light-irradiation,[11, 12] use of an electric field,[13, 14] thermal treatment [15] and treatment with solvent.[16] However, reversible switching between superhydrophilicity and superhydrophobicity has never been reported. Herein we show the roughness-enhanced thermally responsive wettability of a poly (N-isopropylacrylamide)(PNIPAAm)-modified surface.[17, 18] Reversible switching between superhydrophilicity and superhydrophobicity can be achieved in a narrow temperature range of about 108C, which is considered to result from the combined effect of the chemical variation of the surface, and surface roughness. Such switchable surfaces may have wide applications in functional textiles, intelligent microfluidic switching, controllable drug release, and thermally responsive filters. Surface-initiated atom-transfer radical polymerization [19, 20] was used to fabricate thermally responsive PNI-PAAm thin films [21–24] on both a flat and a rough silicon substrate. Results from atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that the thickness of the PNIPAAm thin film could be well controlled by the polymerization time. Figure 1 a (left) shows a typical SEM image of a rough substrate that has been modified with a PNIPAAm thin film. Compared with the smooth surface (Figure 1a right) of the flat substrate, the rough substrate exhibits a regular array of square silicon microconvexes (bright squares). The dark lines are microgrooves that are about 6 μm in width and about 5 μm in depth. These microgrooves were generated by a laser cutter (see Experimental Section) on a silicon wafer in a region of about 1 1 cm2. The surface roughness can be adjusted by controlling the spacing between the grooves. In our experiments, different groove spacings of about 31 μm, 18 μm, 8 μm, and 6 μm were selected. The magnified image of the rough surface shows that both microconvexes and microgrooves were also rather rough (Figure 1b). Further magnified SEM images of the silicon microconvexes before (Figure1c) and after (Figure1d) PNIPAAm polymerization show that these