Samanta Satyabrata, Locklin Jason
Department of Chemistry and Faculty of Engineering, University of Georgia, Athens, Georgia 30602, USA.
Langmuir. 2008 Sep 2;24(17):9558-65. doi: 10.1021/la8017387. Epub 2008 Jul 19.
In this article, we described a method for the formation of photochromic polymer brushes grafted from oxide surfaces using surface-initiated ring-opening metathesis polymerization of spiropyran-based monomers in the presence of second generation Grubbs catalyst. The growth of the polymer film, as monitored by ellipsometry and atomic force microscopy (AFM), is strongly influenced by the initial concentrations of the catalyst and monomer, as well as reaction time. These densely packed and highly smooth polymer films were successfully used as surfaces with switchable color and wettability using light as the external stimulus. The relatively nonpolar spiropyran can be switched to a polar, zwitterionic merocyanine isomer (with a larger dipole moment) using light of the appropriate wavelength. This process is reversible and can be switched back using visible light. The spiropyran-merocyanine photoinduced isomerization gives a reversible contact angle change up to 15 degrees for smooth Si/SiO 2 substrate under sequential irradiation cycles with UV and visible light. This contact angle change can be amplified by complexing the merocyanine form with metal ions through the phenolate oxygen, which enhances the switching of wettability with these polymer brushes. Irradiation in the presence of cobalt(II) ions gives rise to a contact angle variation as high as 35 degrees . This is the largest change in photoinduced surface wettability observed for a flat substrate. Photoisomerization in spiropyrans also yields a change in the refractive index of the film, which we have investigated using ellipsometric imaging. Lastly, morphological changes accompanying photochromism were investigated using atomic force microscopy. Significant morphological changes can only be induced in the films by irradiating in polar solvents that help to stabilize the merocyanine ring open form.
在本文中，我们描述了一种在第二代格拉布催化剂存在下，通过基于螺吡喃的单体的表面引发开环易位聚合，从氧化物表面接枝形成光致变色聚合物刷的方法。通过椭偏仪和原子力显微镜（AFM）监测，聚合物膜的生长受到催化剂和单体的初始浓度以及反应时间的强烈影响。这些紧密堆积且高度光滑的聚合物膜成功地用作具有可切换颜色和润湿性的表面，以光作为外部刺激。相对非极性的螺吡喃可以使用适当波长的光切换为极性的两性离子部花青异构体（具有更大的偶极矩）。这个过程是可逆的，可以使用可见光切换回来。在紫外光和可见光的连续照射循环下，螺吡喃 - 部花青光致异构化使光滑的Si/SiO₂衬底的接触角可逆变化高达15度。通过酚盐氧将部花青形式与金属离子络合，可以放大这种接触角变化，这增强了这些聚合物刷的润湿性切换。在钴（II）离子存在下进行照射会导致接触角变化高达35度。这是在平坦衬底上观察到的光致表面润湿性的最大变化。螺吡喃中的光异构化还会导致膜的折射率发生变化，我们使用椭偏成像对此进行了研究。最后，使用原子力显微镜研究了伴随光致变色的形态变化。只有在有助于稳定部花青开环形式的极性溶剂中照射，才能在膜中诱导出显著的形态变化。
