Viscosity and fragility of confined polymer nanocomposites: a tale of two interfaces.
Viscosity and fragility of confined polymer nanocomposites: a tale of two interfaces.
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DOI：
10.1039/c8nr10362c
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发表时间：
2019-04
期刊：
影响因子：
6.7
通讯作者：
Nimmi Das A;N. Begam;Mohd Ibrahim;S. Chandran;Venkat Padmanabhan;M. Sprung;J. Basu
中科院分区：
文献类型：
--
作者：
Nimmi Das A;N. Begam;Mohd Ibrahim;S. Chandran;Venkat Padmanabhan;M. Sprung;J. Basu
粘度和脆性是决定玻璃态聚合物和聚合物纳米复合材料加工性和热机械稳定性的关键参数。在受限聚合物中，这些参数在很大程度上是由吸附在基质-聚合物界面上的聚合物的长弛豫时间决定的。另一方面，对于聚合物纳米复合材料来说，纳米粒子与周围基质链之间的界面层不仅控制着纳米粒子的形态和分散性，而且还控制着粘度和玻璃化转变温度等各种参数。因此，受限的PNC为研究这两个独立的界面效应的相互作用提供了一个独特的机会。在这里，我们报告了基于X射线散射的PNC薄膜的动力学测量结果，具有两个IL宽度，揭示了这两个界面对测量的粘度和脆性的微妙相互作用。结合粗粒分子动力学(MD)模拟，我们的实验结果表明，PNC膜的粘度随IL宽度和吸附在衬底界面的聚合物层厚度的增加而增加。然而，尽管根据脆性估计，具有较高IL宽度的原始PS和PNC都会变得更坚固，但具有较低IL宽度的PNC显示出随着限制的增加而增加的脆性。我们的结果提供了一种新的方法来控制PNC涂层的热机械性能和稳定性，即通过独立地控制无热玻璃PNC中的两种界面效应。
Viscosity and fragility are key parameters determining the processability and thermo-mechanical stability of glassy polymers and polymer nanocomposites (PNCs). In confined polymers, these parameters are largely dominated by the long relaxation times of the polymers adsorbed at the substrate-polymer interface. On the other hand, for polymer nanocomposites, the interface layer (IL) between the nanoparticles and the surrounding matrix chains often control not only the morphology and dispersion but also various parameters like viscosity and glass transition temperature. Confined PNCs, hence, present a unique opportunity to study the interplay of these two independent interfacial effects. Here, we report the results of X-ray scattering based dynamics measurements of PNC thin films, with a two IL width, unraveling the subtle interplay of these two interfaces on the measured viscosity and fragility. Coupled with coarse-grained molecular dynamics (MD) simulations, our experimental results demonstrate that the viscosity of the PNC films increases with both the IL width and the thickness of the polymer layer adsorbed at the substrate interface. However, while both pristine PS and PNCs with a higher IL width become stronger glasses, as estimated by their fragility, the PNC with a lower IL width shows an increase in fragility with increasing confinement. Our results suggest a novel method to control thermo-mechanical properties and stability of PNC coatings by independently controlling the two interfacial effects in athermal glassy PNCs.