Liu Andong, Goktekin Esma, Gleason Karen K
Department of Chemical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Langmuir. 2014 Dec 2;30(47):14189-94. doi: 10.1021/la503343x. Epub 2014 Nov 17.
Poly(fluoroalkyl acrylate)s with long perfluorooctyl pendant groups have been found to lead to the release of biopersistent perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Those with no more than six perfluorinated carbons in pedant groups do not cause such problems. They, however, give poor dynamic water repellency due to extensive reorganization of surface fluorinated groups when exposed to the water interface. In this work, thin films exhibiting improved dynamic water repellency, as evidenced by water contact angle (WCA) measurements, were synthesized via substrate-independent initiated chemical vapor deposition (iCVD) from 1H,1H,2H,2H-perfluorooctyl acrylate (C6PFA) and divinylbenzene (DVB) using two methods: copolymerization and ultrathin grafted gradation. The copolymerization between C6PFA and the cross-linker, DVB, was confirmed by Fourier transform infrared (FTIR) spectroscopy. The cross-linking is concluded to hinder the reorganization of surface fluorinated groups. The grafted gradation, consisting of an ultrathin pC6PFA top layer and a pDVB base layer, was characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS) measurements, which indicated that the top layer of pC6PFA is <2.5 nm thick to achieve the best dynamic water repellency. The outmost surface of this structure is fully covered by fluorinated groups, giving hydrophobicity. Concurrently, thanks to the interlayer grafting and the ultrathinness of the top layer, the fluorinated groups' tendency to migrate away from water interface is sterically blocked by the highly cross-linked pDVB base layer. The proposed approaches effectively reduced WCA hysteresis of C6PFA-based thin film to as low as 26.9° while maintaining sufficient hydrophobicity (advanced WCA of 119.6°). Due to the conformal and substrate-independent nature of iCVD technique, the films could be used to coat textured surfaces to generate superhydrophobicity.
已发现带有长全氟辛基侧基的聚（丙烯酸氟代烷基酯）会导致具有生物持久性的全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS）的释放。那些侧基中全氟碳不超过六个的则不会引发此类问题。然而，当暴露于水界面时，由于表面氟化基团的广泛重组，它们的动态拒水性较差。在这项工作中，通过1H,1H,2H,2H - 全氟辛基丙烯酸酯（C6PFA）和二乙烯基苯（DVB），采用两种方法——共聚和超薄接枝渐变，通过与基底无关的引发化学气相沉积（iCVD）合成了薄膜，水接触角（WCA）测量证明其具有改善的动态拒水性。通过傅里叶变换红外（FTIR）光谱证实了C6PFA与交联剂DVB之间的共聚。得出交联作用会阻碍表面氟化基团重组的结论。由超薄的pC6PFA顶层和pDVB基层组成的接枝渐变结构通过角分辨X射线光电子能谱（ARXPS）测量进行表征，结果表明pC6PFA顶层厚度小于2.5 nm时可实现最佳动态拒水性。该结构的最外表面完全被氟化基团覆盖，从而具有疏水性。同时，由于层间接枝和顶层的超薄性，高度交联的pDVB基层在空间上阻止了氟化基团从水界面迁移的趋势。所提出的方法有效地将基于C6PFA的薄膜的WCA滞后降低至低至26.9°，同时保持足够的疏水性（前进接触角为119.6°）。由于iCVD技术的保形性和与基底无关的特性，这些薄膜可用于涂覆有纹理的表面以产生超疏水性。
