Thermoresponsive surfaces by spin-coating of PNIPAM-co-PAA microgels: A combined AFM and ellipsometry study
Thermoresponsive surfaces by spin-coating of PNIPAM-co-PAA microgels: A combined AFM and ellipsometry study
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DOI：
10.1016/j.polymer.2007.12.025
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发表时间：
2008-02
期刊：
影响因子：
4.6
通讯作者：
Stephan Schmidt;H. Motschmann;T. Hellweg;R. Klitzing
中科院分区：
文献类型：
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作者：
Stephan Schmidt;H. Motschmann;T. Hellweg;R. Klitzing
将交联共聚物聚（n-异丙基丙烯酰胺-共丙烯酸）（P(NIPAM-co-AA)）组成的微凝胶自旋涂覆在硅片上，制备了热敏涂层。用两种不同的交联剂摩尔比合成了微凝胶，并在pH为2的条件下制备了薄膜。在这个pH值下，粒子带负电仅仅是由于聚合所用的发酵剂。扫描力显微镜（AFM）图像显示颗粒密集堆积，在吸附状态下具有很强的平坦性。对于含有较少交联剂的微凝胶，这种效应更强。由这些微凝胶颗粒组成的涂层在NIPAM的较低临界溶液温度（LCST）区域表现出可逆的热响应性膨胀/收缩。对于这一过程的椭偏研究，一个标准设置被修改，以允许在液体电池的光学厚度的温度依赖的测量。当交联剂用量较少时，微凝胶的温度诱导转变更为明显，并随着交联剂用量的增加而逐渐消失。在pH值为2时，颗粒没有发生明显的解吸，这是由椭圆偏振测量前后干燥膜的AFM显示的。在干燥状态下，制备的膜的平均厚度约为30nm，在膨胀状态下达到约400nm的厚度。
Thermosensitive coatings are fabricated by spin-coating of microgels consisting of the cross-linked copolymer poly(N-isopropyl acrylamide-co-acrylic acid) (P(NIPAM-co-AA)) on silicon wafers. The microgels were synthesized with two different cross-linker molar ratios and the thin films were prepared at pH 2. At this pH the particles are negatively charged only due to the starter used for the polymerization. Scanning force microscopic (AFM) images indicate a dense packing of the particles and a strong flattening in the adsorbed state. This effect is stronger for microgels containing less cross-linker. Coatings consisting of these microgel particles show a reversible thermoresponsive swelling/shrinking in the region of the lower critical solution temperature (LCST) of NIPAM. For the ellipsometric study of this process a standard setup was modified in order to allow temperature dependent measurements of the optical thickness in a liquid cell. The temperature induced transition is sharper in the case of microgels with lower amount of cross-linker and smears out with increasing amount of cross-linker. No significant desorption of the particles occurs at pH 2, which was shown by AFM of the dried films before and after the ellipsometric measurements. In the dry state the average thickness of the prepared films is approximately 30nm and a thickness of about 400nm is reached in the swollen state.