Xu Quanyin, Zhu Ningtao, Fang Huasong, Wang Xinping, Priestley Rodney D, Zuo Biao
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, 310018, China.
Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States.
ACS Macro Lett. 2021 Jan 19;10(1):1-8. doi: 10.1021/acsmacrolett.0c00760. Epub 2020 Dec 7.
The film thickness and substrate interface are the two most common parameters to tune the dynamics of supported thin films. Here, we investigated the glass transition temperature () and thermal expansion of thin poly(methyl methacrylate) (PMMA) films with various thicknesses and different interfacial effects. We showed that, although the of the thin films can be modulated equivalently by the two factors, their ability to change the expansivity (β) is quite different; that is, β increases notably with a reduction in the thickness, while it is insensitive to perturbations at the interface. We attribute the deviation in modulating β by the thickness and the interfacial effect to the disparate abilities to change the free volume content in the film by a free surface and substrate interface. This leads to a situation where thin films with dissimilar thicknesses and interfacial properties can have the same but very different β values, suggesting that alone cannot unequivocally quantify thin film dynamics.
薄膜厚度和基底界面是调节支撑薄膜动力学的两个最常见参数。在此，我们研究了具有不同厚度和不同界面效应的聚甲基丙烯酸甲酯（PMMA）薄膜的玻璃化转变温度（）和热膨胀。我们表明，尽管薄膜的可以由这两个因素等效调节，但其改变膨胀系数（β）的能力却大不相同；也就是说，β随厚度减小而显著增加，而对界面处的扰动不敏感。我们将通过厚度和界面效应调节β时的偏差归因于自由表面和基底界面改变薄膜中自由体积含量的不同能力。这导致了一种情况，即具有不同厚度和界面性质的薄膜可以具有相同的，但β值却非常不同，这表明仅靠不能明确地量化薄膜动力学。
