Departamento de Química Física I, Facultad de Química, Universidad Complutense, 28040-Madrid, Spain.
Phys Chem Chem Phys. 2011 May 28;13(20):9534-9. doi: 10.1039/c1cp20305c. Epub 2011 Apr 12.
We report an experimental study that points out the existence of a fluid to soft-glass transition in Langmuir polymer monolayers of poly(methyl methacrylate) (PMMA), for which the water/air interface behaves as a poor-solvent. The temperature dependence of surface pressure vs. surface area equilibrium isotherms shows a glass-like transition temperature at T(g,2D)≈ 298 K, significantly lower than the value for bulk PMMA (T(g,bulk)≈ 378 K). The plot of the film thickness h vs. temperature shows a sharp change of slope at about the same temperature, 298 K, which is a typical hallmark of a glass transition in thin polymer films [J. L. Keddie, R. A. L. Jones, R. A. Cory, Europhys. Lett., 1996, 27, 59-64]. Furthermore, slightly above T(g,2D), the temperature dependence of the dilational viscosity does not follow an Arrhenius law, but instead can be described by a Vogel-Fulcher-Tamman equation with parameters that are typical of a fragile glass. Not only the qualitative behavior of three distinct equilibrium and dynamic properties, but also the quantitative agreement of the values of T(g) obtained, are a strong evidence of the existence of a fluid to soft-glass transition in this quasi-2D system.
我们报告了一项实验研究，指出聚甲基丙烯酸甲酯（PMMA）的 Langmuir 聚合物单分子层中存在流体到软玻璃转变，其中水/空气界面表现为不良溶剂。表面压力与表面面积平衡等温线的温度依赖性显示玻璃转变温度 T(g,2D)≈298 K，明显低于本体 PMMA 的值（T(g,bulk)≈378 K）。膜厚 h 随温度的变化图在大约相同的温度 298 K 处出现斜率的急剧变化，这是薄聚合物膜中玻璃转变的典型特征[J. L. Keddie, R. A. L. Jones, R. A. Cory, Europhys. Lett., 1996, 27, 59-64]。此外，在略高于 T(g,2D)处，膨胀粘度的温度依赖性不遵循阿仑尼乌斯定律，而是可以用 Vogel-Fulcher-Tamman 方程来描述，其参数是脆性玻璃的典型特征。不仅三种不同平衡和动态性质的定性行为，而且获得的 T(g)值的定量一致性，都是在这个准二维系统中存在流体到软玻璃转变的有力证据。
