Department of Chemistry, Key Laboratory of Advanced Textile Materials and Manufacturing Technology of Education Ministry, Zhejiang Sci-Tech University, Hangzhou 310018, China.
Soft Matter. 2016 Jul 13;12(28):6120-31. doi: 10.1039/c6sm00881j.
Despite its importance in the processing of nanomaterials, the rheological behavior of thin polymer films is poorly understood, partly due to the inherent measurement challenges. Herein, we have developed a facile method for investigating the rheological behavior of supported thin polymeric films by monitoring the growth of the "wetting ridge"-a microscopic protrusion on the film surface due to the capillary forces exerted by a drop of ionic liquid placed on the film surface. It was found that the growth dynamics of the wetting ridge and the behavior of polystyrene rheology are directly linked. Important rheological properties, such as the flow temperature (Tf), viscosity (η), and terminal relaxation time (τ0) of thin polystyrene films, can be derived by studying the development of the height of the wetting ridge with time and the sample temperature. Rheological studies using the proposed approach for supported thin polystyrene (PS) films with thickness down to 20 nm demonstrate that the PS thin film exhibits facilitated flow, with reduced viscosity and lowered viscous temperature and a shortened rubbery plateau, when SiOx-Si was used as the substrate. However, sluggish flow was observed for the PS film supported by hydrogen-passivated silicon substrates (H-Si). The differences in enthalpic interactions between PS and the substrates are the reason for this divergence in the whole-chain mobility and flow ability of thin PS films deposited on SiOx-Si and H-Si surfaces. These results indicate that this approach could be a reliable rheological probe for supported thin polymeric films with different thicknesses and various substrates.
尽管在纳米材料处理中具有重要意义，但由于固有的测量挑战，薄聚合物薄膜的流变行为仍未得到很好的理解。在此，我们开发了一种简便的方法，通过监测“润湿脊”（由于放置在薄膜表面上的离子液体滴产生的毛细力在薄膜表面上形成的微观突起）的生长来研究支撑的薄聚合物薄膜的流变行为。结果发现，润湿脊的生长动力学与聚苯乙烯流变行为直接相关。通过研究润湿脊高度随时间和样品温度的发展，可以得出重要的流变性质，例如薄聚苯乙烯薄膜的流动温度（Tf）、粘度（η）和末端松弛时间（τ0）。使用提出的方法对厚度低至 20nm 的支撑的薄聚苯乙烯（PS）薄膜进行流变学研究表明，当使用 SiOx-Si 作为基底时，PS 薄膜表现出促进流动，粘度降低，粘性温度降低，橡胶平台缩短。然而，对于由氢化硅（H-Si）支撑的 PS 薄膜，则观察到流动缓慢。PS 与基底之间的焓相互作用的差异是导致 PS 薄膜在 SiOx-Si 和 H-Si 表面上沉积时整个链的迁移率和流动能力差异的原因。这些结果表明，该方法可以成为不同厚度和各种基底的支撑的薄聚合物薄膜的可靠流变探针。
