Direct experimental evidences of the density variation of ultrathin polymer films with thickness

POLYMER

卷:228

Article

Giermanska, Joanna¹  Ben Jabrallah, Soumaya^2,3  Delorme, Nicolas³  Vignaud, Guillaume²  Chapel, Jean-Paul¹ 

[1] Univ Bordeaux, Ctr Rech Paul Pascal, CNRS, UMR 5031, F-33600 Pessac, France

[2] Univ Bretagne, IRDL, FRE CNRS 3744, F-56100 Lorient, France

[3] Le Mans Univ, Inst Mol & Mat Mans, IMMM, UMR,CNRS 6283, Ave Olivier Messiaen, F-72085 Le Mans 9, France

关键词: Polymer thin film;    Density variation;    Quartz crystal microbalance;   

DOI  :  10.1016/j.polymer.2021.123934

来源: Elsevier

【 摘 要 】

Beyond the peculiar glass transition temperature (Tg) studied extensively for over two decades, we have investigated in this work the variation of the mass density of polymer thin films, a key property barely put forward in the literature. We were able to directly measure the mass density of polystyrene (PS) and poly (methyl methacrylate) (PMMA) thin films as a function of their thickness from accurate Quartz Crystal Microbalance (QCM) dissolution experiments. Depending on the chemical nature of the polymers, the results showed an unambiguous variation of the mass density when the film thickness was reduced: an increase for PS and a decrease for PMMA films. In the last part, we measured the coefficient of thermal expansion (CTE) of both polymers to rationalize the apparent inconsistency of an increase/decrease in the mass density with the commonly observed depression/rise of the Tg of PS/PMMA films. Surprisingly, the coefficient of thermal expansion and the mass density showed a similar variation with thickness, pointing out a clear correlation between the glass transition temperature, the coefficient of thermal expansion and the free volume of the polymer.

【 授权许可】

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