Interfacial Dynamics in Supported Ultrathin Polymer Films—From the Solid to the Free Interface
Interfacial Dynamics in Supported Ultrathin Polymer Films—From the Solid to the Free Interface
复制标题
支持超薄聚合物薄膜中的界面动力学——从固体界面到自由界面
DOI：
10.1021/acs.jpclett.0c03211
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Sangoro, Joshua
中科院分区：
文献类型：
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作者：
Mapesa, Emmanuel Urandu;Shahidi, Nobahar;Kremer, Friedrich;Doxastakis, Manolis;Sangoro, Joshua
利用纳米结构电极进行宽带介电光谱测量和原子分子动力学模拟，研究了超薄层中的分子动力学。使用聚醋酸乙烯酯作为模型体系，并利用在玻璃化转变温度Tg以上的扩展温度范围内弛豫时间的分布，我们证明，尽管在12 nm薄膜厚度下，节段弛豫的平均速率仍然保持块体状，但界面区域的分子迁移率发生了改变。结合模拟和实验结果，我们明确地表明，由吸附的聚合物片段引起的慢弛豫和归因于自由界面附近片段的快弛豫模式都具有非阿伦尼乌斯温度激活。这些界面区域的厚度为~ 1.5 nm，每个都略高于量热，与分子量和膜厚度无关。这些界面上的偏差与聚合物在粘附、涂层和聚合物纳米复合材料中的应用有关。
Molecular dynamics in ultrathin layers is investigated using nanostructured electrodes to perform broadband dielectric spectroscopy measurements, and by atomistic molecular dynamics simulations. Using poly(vinyl acetate) as the model system and taking advantage of access to the distribution of relaxation times in an extended temperature range above the glass transition temperature,Tg, we demonstrate that while the mean rates of the segmental relaxation remain bulklike down to 12 nm film thickness, modified molecular mobilities arise in the interfacial zones. Combining results from simulations and experiments, we show unambiguously that both the slow relaxations arising from adsorbed polymer segments and the faster modes attributed to segments in the vicinity of the free interface have non-Arrhenius temperature activation. These interfacial regions span thicknesses of ∼1.5 nm each just above the calorimetricTgindependent of molecular weight and film thickness. These deviations at interfaces are relevant for applications of polymers in adhesion, coatings, and polymer nanocomposites.