探索原位研究聚合物超薄膜黏弹性及其分子运动的新方法

Thin polymer films have striking dynamical properties that differ from their bulk counterparts. Optimizing the functionality of nano-materials and micro-manufacturing of polymer nano-devices require a broad understanding of the dynamics of polymer chains under confinement in the thin-film geometry. The molecular motion in nano-confined systems is a relatively new topic and object of intense scientific debate. Although an amount of knowledge has been achieved, no generally accepted theory exists and the dynamics related with thin polymer films remain a pending problem in polymer condensed matter research. Consequently, there is a great demand for novel approaches based on various mechanisms to characterize the viscoelasticity and molecular motion of polymer thin film. This project firstly presented an entirely new method to in-situ study the viscoelasticity and molecular motion of polymer thin film by researching the wetting-ridge growth dynamic. The evolution of wetting ridge on polymer film surface with different molecular weight and at various temperatures by a liquid droplet which is thermodynamically immiscible with the polymer was systematically investigated in this project. The creep model is employed to analyze the development process of wetting ridge, and several quantitative parameters such as wetting ridge linear increment velocities (k), characteristic relaxation time (τ*) and characteristic deformation temperature (T*) are put forward to describe the growth dynamics of wetting ridge. The inherent relationships between these parameters and viscoelasticity, molecular relaxation of polymer films are explored, and the physical meanings of these parameters are clarified. The aim of this project is to develop an original method for in-situ characterizing the viscosity, segmental relaxation time, viscous flow temperature of thin polymer films, as well establish the theoretical foundation of this method. Meanwhile, the effects of film thickness, temperature, molecular weight and substrate chemistry on molecular mobility of thin polymer film were investigated using the developed method, for seeking the physical mechanism of the molecular motion of thin polymer films. This study would provide a new method measuring the molecular motion of thin polymer film; as well deepen our understanding of polymer chain motion under geometrical confinement.

聚合物薄膜具有与本体不同的分子运动行为。聚合物薄膜分子运动对于聚合物纳米材料的性能调控及成型、加工等具有重要意义，是当前高分子物理领域的研究热点。目前，聚合物薄膜分子运动的物理机制仍不清楚；不同研究方法的结果不能很好的统一。发展研究聚合物薄膜分子运动的新方法是当务之急。本项目首次提出通过研究聚合物薄膜表面润湿脊（wetting ridge）形成动力学，原位研究薄膜黏弹性及分子运动行为。项目研究与聚合物不相容的液滴在聚合物表面润湿脊的形成与生长过程及其与温度、分子量等的关系；利用蠕变模型分析润湿脊发展过程，关联润湿脊线性增长速率、特征松弛时间、特征形变温度等特征参量与聚合物黏弹性及分子松弛的本质关系，发展一种原位测量高分子薄膜黏度、松弛时间、黏流温度的新方法，奠定其理论基础。并利用该法研究膜厚、温度、分子量、基底性质对薄膜分子运动的影响，探索一维受限聚合物薄膜分子松弛的物理机制。

项目主要研究液滴表面张力作用下不同温度聚合物薄膜润湿脊的生长（或形成）动力学，关联其与聚合物黏弹性及链松弛的本质关系；发展一种测量高分子超薄膜黏度和分子运动的新方法。并利用该法研究膜厚、聚合物结构、分子量、基底性质等对聚合物超薄膜黏度及高分子链松弛等的影响，探索一维受限高分子链运动的物理机制。主要获得了以下成果：（1）发现了润湿脊生长动力学与聚合物黏弹性的本质联系，提出了以润湿脊高度线性增长的斜率（k）来表征润湿脊生长速率，关联了k与聚合物薄膜黏度（η）的定量关系式（k = αγsinθ/η, α为常数，γ为测试液体表面张力，θ为液滴接触角），发展了一种通过监控润湿脊生长研究聚合物超薄膜黏度的新方法。利用该法可以实现不同基材表面不同厚度聚合物薄膜黏度及黏流温度的直接测量，具有重要应用前景。基于该方法，我们系统研究了聚合物超薄膜黏弹性及分子运动行为，（2）阐明了高分子/基底界面相互作用、聚合物分子量对高分子超薄膜黏弹性及分子运动影响的本质；（3）揭示了界面吸附层结构对聚合物超薄膜分子运动的影响。（4）同时，还利用和频振动光谱、椭圆偏振光谱仪、掠入射X-射线衍射等辅助表征手段揭示了聚合物分子刷聚集态结构形成的控制因素及其玻璃化转变行为随分子量及接枝密度变化的基本规律；获得了基底界面高分子链构象松弛行为，阐明了薄膜制样方式对界面分子运动行为的影响。项目研究成果为表征聚合物超薄膜黏弹性及分子运动提供了新方法，也为深入理解纳米受限高分子的结构与动力学行为提供了新的见解。项目共发表论文14篇，其中Macromolecules 6篇, Soft Matter 3篇，J. Phys. Chem. B 1篇； J. Chem. Phys. 1 篇； J. Phys. Chem. C 1 篇； Langmuir 1 篇； 中国科学：化学 1 篇; 培养硕士生5名。