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Switching Water Droplet Adhesion Using Responsive Polymer Brushes Xinjie Liu,†,‡ Qian Ye,† Bo Yu,† Yongmin Liang,† Weimin Liu,† and Feng Zhou*,† †
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China, and ‡Graduate College of Chinese Academy of Sciences, Beijing 100083, P. R. China Received May 13, 2010. Revised Manuscript Received June 4, 2010 Two stimuli-responsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(dimethylamino)ethyl methacrylate (PDMAEMA), were grafted from initiator-modified anodized alumina substrates with irregular micro/ nanoscale surface topography. The resulting polymer-coated surfaces exhibited highly unusual wettability properties, as spherical water/acid/alkali/salt droplets could be reversibly switched between pinned states and rolling states due to the changes of temperature, pH, and electrolytes. The key to this effect is the combination of a mixed monolayer which provides initiator points for brush growth as well as a permanently hydrophobic substrate and a surface roughness.
Introduction The superhydrophobicity and self-cleaning properties exhibited by lotus leaves,1,2 feathers of birds,3,4 and the wings of insects5 have generated a plethora of artificial surfaces that mimick these natural materials. These surfaces are self-cleaning because water droplets exhibit not only very high (>150°) contact angles (CAs) but also very low (150°) for all mixed monolayer samples, but the mobility can be tuned from SAs of 90° (1:5) to 39° for initiator:PFOTS ratio of 1:8, and by further increasing the contribution of the hydrophobic SAM (1:15 ratio), the sliding angle decreased to around 10° (Figure 3d). The 1:15 initiator: PFOTS surface shows
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Langmuir 2010, 26(14), 12377–12382
DOI: 10.1021/la101909e
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surface composition, while very low SAs (
