Tannenbaum R, King S, Lecy J, Tirrell M, Potts L
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Langmuir. 2004 May 25;20(11):4507-14. doi: 10.1021/la036137v.
In this paper, we studied the kinetics of the adsorption of poly(methyl methacrylate), PMMA, onto native aluminum oxide surfaces by X-ray photoelectron spectroscopy and reflection-absorption infrared spectroscopy, with the intent of tracking the various changes observed in the infrared spectrum of the adsorbed polymer layer as a function of adsorption time. Specifically, we utilized the relative changes in the absorption bands of the carbonyl, carboxylic acid, and carboxylate groups to determine the sequence of events that culminate in the formation of bonds between carboxylate groups on hydrolyzed PMMA and specific sites on the aluminum oxide surface. We have shown that the adsorption process involves the hydrolysis of a fraction of the methoxy groups of the PMMA to generate COOH groups. Unlike previous assumptions, the formation of COOH groups on the PMMA chains does not constitute a sufficient condition for the actual chemisorption of the polymer chains onto the metal oxide surface. To promote bonding, the acid groups must undergo dissociation to form the carboxylate groups, followed subsequently by actual bond formation, that is, active anchoring, on the surface. This process is mediated by the aluminum oxide sites on the surface in the presence of water. Hence, the adsorption process occurs via a two-step mechanism, in which the first step, that is, the hydrolysis step, is a necessary but insufficient condition and the second step, that is, the anchoring step, is largely dependent on the type of interfacial chemistry possible for a particular polymer-metal oxide surface, the polymer conformation, the molecular weight, and the flexibility of the adsorbing molecules.
在本文中，我们通过X射线光电子能谱和反射吸收红外光谱研究了聚甲基丙烯酸甲酯（PMMA）在天然氧化铝表面的吸附动力学，旨在追踪吸附聚合物层红外光谱中观察到的各种变化与吸附时间的函数关系。具体而言，我们利用羰基、羧酸和羧酸盐基团吸收带的相对变化来确定一系列事件的顺序，这些事件最终导致水解PMMA上的羧酸盐基团与氧化铝表面的特定位点形成键。我们已经表明，吸附过程涉及PMMA的一部分甲氧基水解生成COOH基团。与先前的假设不同，PMMA链上COOH基团的形成并不构成聚合物链实际化学吸附到金属氧化物表面的充分条件。为了促进键合，酸基团必须解离形成羧酸盐基团，随后在表面上进行实际的键形成，即活性锚定。这个过程在水存在的情况下由表面的氧化铝位点介导。因此，吸附过程通过两步机制发生，其中第一步，即水解步骤，是必要但不充分的条件，第二步，即锚定步骤，很大程度上取决于特定聚合物-金属氧化物表面可能的界面化学类型、聚合物构象、分子量和吸附分子的柔韧性。
