Viscoelastic Response of Ultrathin Polymer Films: Bubble Inflation, Liquid Dewetting and Molecular Architecture Effects

技术总结：这项工作是一个基本的调查的粘弹性响应的聚合物薄膜在两种不同的条件。这项工作将比较，对比，并寻求由PI在得克萨斯理工大学开发的nanobubble膨胀方法和液体dewetting方法开发的Bodimetry和Fretigny在巴黎（这是唯一的方法，目前可用于测量无支撑膜的粘弹性响应）之间的差异的起源。 这两种技术显示出玻璃化转变温度随薄膜厚度的变化存在显着差异。 这两种方法的不同之处在于，一种测量具有自由表面的膜，另一种测量漂浮在移动的衬底上的膜。计划中的研究将研究改变基底、分子量和分子结构对聚合物薄膜粘弹性的影响。它将探索约束行为的相关差异与表面能/表面相互作用的非常微妙的差异有关的假设，并将提供新的数据，重点是了解表面和界面如何影响限制在纳米尺寸尺度的聚合物的动力学。纳米级限制对材料行为的巨大影响通过显示巨大性质变化的聚合物薄膜的响应来举例说明，例如，在具有纳米厚度的自由悬浮膜中。 然而，这些变化的起源尚未阐明。 本工作使用两种新的纳米力学测试方法探测这些变化。 这项工作比较和对比了一系列具有不同分子特性的聚合物的机械性能。此外，因为存在由膜表面看到的环境的如此强烈的明显影响，所以该工作探测了暴露于具有不同性质的液体的可固化聚合物膜的行为。这项研究为理解表面和界面如何影响局限于纳米尺度的聚合物力学提供了新的数据。 该项目还有一个重要组成部分，即培训研究生，除了科学培训外，还通过德克萨斯理工大学的“科学：这是女孩的事”项目，让他们参与面向年轻女孩的STEM推广项目。

TECHNICAL SUMMARY: The work is a fundamental investigation of the viscoelastic response of ultrathin polymer films in two different conditions. The work will compare, contrast, and seek origins of differences between the nanobubble inflation method developed by the PI at Texas Tech University and the liquid dewetting method developed by Bodiguel and Fretigny in Paris (which are the only methods currently available to measure the viscoelastic response of unsupported films). The two techniques had shown substantial differences in glass transition temperatures as functions of film thickness. The two methods differ in that one measures films with free surfaces and the other measures films floating on a mobile substrate. The planned research will examine the effects of changing substrate, molecular weight, and molecular architecture on the viscoelastic properties of ultrathin polymer films. It will explore the hypothesis that the relevant differences in confinement behavior are related to very subtle differences in surface energy/surface interactions and will provide new data focused on the understanding of how surfaces and interfaces impact the dynamics of polymers confined to the nanometer size scale.NON-TECHNICAL SUMMARY: The dramatic influence of nanoscale confinement on material behavior is exemplified by the response of ultrathin polymer films that show tremendous property changes, for example, in freely suspended films having nanometer thicknesses. Yet the origins of these changes are not yet elucidated. The present work probes these changes using two novel nanomechanical test methods. The work compares and contrasts mechanical properties of a series of polymers having different molecular characteristics. In addition, because there is such a strong apparent effect of the environment seen by the film surface, the work probes the behavior of the ultrathin polymer films exposed to liquids having different properties. The research provides new data in the understanding of how surfaces and interfaces impact the mechanics of polymers confined to the nanometer size scale. The project also has an important component that trains graduate students and, in addition to their scientific training, involves them in a STEM outreach program to young girls through the "Science: It's a Girl Thing" Program at Texas Tech University.