Bio-IT Convergence Center, Korea Institute of Ceramic Engineering and Technology, Seoul 153-801, Korea.
Langmuir. 2011 Apr 5;27(7):3638-53. doi: 10.1021/la104840c. Epub 2011 Mar 7.
Immersion of oxidized aluminum substrates in ethanol solutions of poly(acrylic acid) (PAA), followed by extensive solvent immersion, results in tenaciously chemisorbed, nanometer scale, controllable thickness films for a wide range of solution concentrations and molecular weights. Atomic force microscope images reveal isolated polymer globules from adsorption in low-concentration solutions with crossover to conformal, highly uniform, nanometer-thickness films at higher concentrations, an indication that the chemisorbing chains start to overlap and trap underlying segments to form planar chemisorbed films only two or three chains in thickness. Quantitative IR reflection spectroscopy in combination with chemical derivitization on a standard set of 1.0(±0.2) nm thick films reveals a film structure with 5.5(±1) chemisorbed -CO(-)(2) groups/nm(2) and 6.3 unattached -CO(2)H groups/nm(2), with up to ∼3.6/nm(2) available for chemical derivitization, a comparable number to typical self-assembled monolayer coverages of ∼4-5 molecules/nm(2). Thermal treatment of the ∼1 nm chemisorbed films, at even extreme temperatures of ∼150 °C, results in almost no anhydride formation via adjacent -CO(2)H condensation, in strong contrast to bulk PAA, a clear indication that the films have a frozen glass structure with effectively no segment and side group mobility. Overall, these results demonstrate that these limiting thickness nanometer films provide a model surface for understanding the behavior of strongly bound polymer chains at substrates and show potential as a path to creating highly stable, chemically functionalized inorganic substrates with highly variable surface properties.
将氧化铝基底浸入聚丙烯酸（PAA）的乙醇溶液中，然后进行长时间的溶剂浸泡，会得到牢固化学吸附的纳米级、厚度可控的薄膜，适用于广泛的溶液浓度和分子量范围。原子力显微镜图像显示，在低浓度溶液中，吸附是孤立的聚合物小球，而在较高浓度下，会转变为共形的、高度均匀的纳米级厚度薄膜，这表明化学吸附的链开始重叠并捕获底层链段，仅形成两到三层厚度的平面化学吸附膜。结合标准的 1.0(±0.2)nm 厚薄膜的化学衍生化的定量红外反射光谱表明，薄膜结构具有 5.5(±1)个化学吸附的 -CO(-)(2)基团/nm(2)和 6.3 个未配位的 -CO(2)H 基团/nm(2)，最多有 ∼3.6/nm(2)可用于化学衍生化，这与典型的自组装单层覆盖度（∼4-5 个分子/nm(2)）相当。即使在极端温度 ∼150°C 下对约 1nm 厚的化学吸附膜进行热处理，也几乎不会通过相邻 -CO(2)H 缩合形成酐，与块状 PAA 形成鲜明对比，这清楚地表明薄膜具有冻结的玻璃结构，链段和侧基几乎没有迁移性。总的来说，这些结果表明，这些极限厚度的纳米薄膜为理解强结合聚合物链在基底上的行为提供了一个模型表面，并为创建具有高度可变表面性质的高度稳定、化学功能化的无机基底提供了一种途径。
