具有温度响应特性的表面附着Polymer网络亚微米膜
Submicrometric Films of Surface-Attached Polymer Network with Temperature-Responsive Properties
摘要：
研究了表面附着的聚（N-异丙基丙烯酰胺）（PNIPAM）网络膜的温度响应特性。合成包括交联和接枝预形成的烯反应性聚合物链通过硫醇-烯点击化学。表面附着和交联的聚合物膜的形成具有良好控制的优点，而无需任何无氧气氛或添加引发剂的注意。具有相同交联密度的PNIPAM水凝胶膜在从纳米到微米的宽范围厚度上合成。利用椭圆偏振术、中子反射率和原子力显微镜作为互补的表面探测技术，研究了膨胀-塌陷转变随温度的变化。观察到所有亚微米PNIPAM水凝胶膜的急剧和高幅度的温度诱导的相变。对于高于LCST的温度，表面附着的PNIPAM水凝胶类似地塌陷，但没有完全排出水。对于低于LCST的温度，PNIPAM水凝胶的溶胀取决于膜厚度。它示出的溶胀是强烈的表面附着的影响下$\sim$ 150 nm的双金属膜。对于大于150 nm（至微米）的较厚膜，具有相同交联密度的表面附着聚合物网络同样溶胀。水凝胶膜在垂直于基底的方向上的密度分布与自由表面的平面内形貌相面对。其结果是，自由界面宽度远大于水凝胶膜的粗糙度，这表明在自由表面的侧链。
英文摘要：
Temperature-responsive properties of surface-attached poly(N-isopropylacrylamide) (PNIPAM) network films with well-controlled chemistry are investigated. The synthesis consists of cross-linking and grafting preformed ene-reactive polymer chains through thiol--ene click chemistry. The formation of surface-attached and cross-linked polymer films has the advantage of being wellcontrolled without any caution of no-oxygen atmosphere or addition of initiators. PNIPAM hydrogel films with same cross-link density are synthesized on a wide range of thickness, from nanometers to micrometers. The swelling-collapse transition with temperature is studied by using ellipsometry, neutron reflectivity, and atomic force microscopy as complementary surface-probing techniques. Sharp and high amplitude temperature-induced phase transition is observed for all submicrometric PNIPAM hydrogel films. For temperature above LCST, surface-attached PNIPAM hydrogels collapse similarly but without complete expulsion of water. For temperature below LCST, the swelling of PNIPAM hydrogels depends on the film thickness. It is shown that the swelling is strongly affected by the surface attachment for ultrathin films below $\sim$150 nm. For thicker films above 150 nm (to micrometers), surface-attached polymer networks with the same cross-link density swell equally. The density profile of the hydrogel films in the direction normal to the substrate is confronted with in-plane topography of the free surface. It results that the free interface width is much larger than the roughness of the hydrogel film, suggesting pendant chains at the free surface.
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