Materials World Network: Controlling Properties of Polymers in Thin Films

材料世界网络汇集了世界上聚合物薄膜实验表征方面的专业知识(分别是美国波士顿大学和德国弗莱堡大学关于薄膜应力和粘弹性的实验表征)和对受限聚合物动力学和结构的计算机模拟(法国斯特拉斯堡Charles Sadron研究所)，以寻求一幅能够解释迄今观察到的所有不寻常的聚合物薄膜特性(即动力学、残余应力和热膨胀性)的统一图像的可能性，并同时试图将这些特性与聚合物薄膜中的(非平衡)聚合物结构以及制造和/或制造工艺联系起来。通过建立这样的结构-性质和加工-性质关系，该网络的目标是最终制定一种能够预测、设计和调整聚合物薄膜性能的战略。由于据称导致不寻常性能的聚合物薄膜的结构是亚稳态的，并且随着时间的推移而变化，因此使用了一种可交联性的聚苯乙烯共聚物来冻结其结构和由此产生的性能。这项研究在很大程度上是由几个已发表的实验和一个由Reiter(来自德国的PI)和De Gennes猜想的模型指导的，该模型描述了由快速溶剂蒸发产生的非平衡聚合物网络结构如何解释负热膨胀系数。这一计划的结果有望证实这一模型，并进一步扩大其与薄膜动力学行为的相关性。由此产生的更具包容性的模型将提供一个关键平台，在该平台上可以描绘和/或制定结构-性能和加工-性能关系。该项目的成功为设计和制造具有预想的热膨胀和/或动态性能的聚合物薄膜提供了一种简单的策略。拥有这样的能力大大增强了我们的优势，使我们能够以经济高效的方式调整这些材料，以适应使用它们的应用对其不断变化的性能要求。六名博士生接受了这个项目的培训，为他们提供了一个极好的培训基础，帮助他们解决与旋涂聚合物薄膜的特殊性能有关的学术挑战和技术相关问题。该网络的成员受益于该方案的国际背景。特别是博士生之间，除了频繁的视频会议外，还有定期的会面和身体交流。该计划积极吸引本科生和高中生参加。该奖项由DMR聚合物项目和DMR特别项目办公室共同资助。

This Materials World Network brings together world-expertise on the experimental characterizations of polymer films (Boston University, USA and Universität Freiburg, Freiburg, Germany on the film stress and viscoelasticity, respectively) and computer simulations on the dynamics and structure of confined polymers (Institut Charles Sadron, Strasbourg, France) to seek for the possibility of a unified picture that can account for all the unusual properties observed of polymer films to date (namely the dynamics, residual stress and thermal expansivity), and at the same time attempt to relate these properties to the (out-of-equilibrium) polymer structures therein as well as the fabrication and/or post-fabrication processes producing them. By establishing such structure-property and processing-property relations, the Network aims to ultimately institute a strategy that can predict, design and tune the properties of polymer films. Because the structures of the polymer films that allegedly cause the unusual properties are metastable and change with time, a cross-linkable copolymer of polystyrene are used to freeze-in the structures and whereby their properties. This research is largely guided by several published experiments and a model conjectured by Reiter (the PI from Germany) and de Gennes portraying how a non-equilibrated polymer network structure engendered by rapid solvent evaporation could explain negative thermal expansivity. The results of this program are expected to substantiate this model, and additionally expand its relevance to the dynamical behaviors of the films. The resultant, more encompassing model will provide a pivotal platform upon which the structure-property and processing-property relations can be portrayed and/or formulated.Applications of polymer films are widespread. Success of this program leads to a simple strategy to design and fabricate polymer films with premeditated thermal expansion and/or dynamical properties. Having such ability significantly enhances our leverage to adapt these materials in a cost effective manner to the ever-changing demands on their properties by the applications employing them. Six PhD students are trained in this program, providing them an excellent training ground in the academically challenging and technologically relevant problem concerning the unusual properties of spin-coated polymer films. Members of the Network benefit from the international setting of the program. In particular, there are regular meetings and physical exchange between the PhD students besides frequent video conferences. This program actively engages undergraduate and high-school student participants. This award is jointly funded by the DMR Polymers Program and the DMR Office of Special Programs.