The Nanomechanical and Viscoelastic Responses of Ultrathin Polymer Films

超薄聚合物薄膜的纳米力学和粘弹性响应

• 批准号: 1610495
• 负责人: Gregory McKenna
• 金额: $ 52.53万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1610495&HistoricalAwards=false
• 关键词: Nanomechanical; Viscoelastic; Responses; Ultrathin; Polymer

NON-TECHNICAL SUMMARY:The technological infrastructure that provides science and engineering solutions to the rapidly growing nanotechnology area is of considerable national interest. The present work addresses fundamentals of the nanoconfinement behavior of materials that form the basis of the relevant enabling technologies. One important set of problems addressed relates to the engineering properties (such as stiffness and yield strength) of nanometer-thick films that are in freely standing form and, consequently, cannot be readily measured. The only method available for making such measurements in such materials is a bubble-inflation method developed in the PI's laboratory that allows testing of extremely small quantities of material, especially nanometer-thin polymer films. The work investigates the engineering properties of freely standing polymer films deep in the glassy state with particular emphasis on yield behavior. These studies will be the first to provide film thickness and temperature dependence of yield in freely standing films. Also, in the freely standing films, a large enhancement in the material stiffness is observed and, recently, conflicting theoretical models of the stiffening behavior have appeared to explain the phenomenon. Such predictions are, of course important to nanomaterial design and use, and the present work will establish the range of validity of these theories. Molecular architecture effects will also be investigated. Finally, the nanobubble inflation experiment permits investigations of novel materials that were previously unachievable due to their extremely small quantities. In this case, the investigators will study ultrastable polymer glasses made by physical vapor deposition (PVD) and that can be made more stable than even a 20 million year old amber glass. This high stability allows the interrogation of a long-standing question whose resolution is fundamental to theories of glasses and, in particular, how to make long-term predictions of their behavior in applications to important areas such as advanced composites and adhesives. TECHNICAL SUMMARY:The behavior of ultrathin polymer films remains an intense area of investigation, but most studies have been limited to the case of substrate-supported films even though studies suggest much larger effects occur in the freely standing state. The present work tests three aspects of freely standing ultrathin films using the TTU bubble inflation method and takes advantage of the method's capability of making viscoelastic measurements on extremely small quantities of material to study the response of an ultrastable polymer glass made by physical vapor deposition (PVD). One important set of problems addressed relates to the engineering properties, such as modulus and yield strength of nanometer thick films that are in freely standing form and, consequently, not readily measured. The only method available for making such measurements in such materials is a bubble inflation method that allows testing of extremely small quantities of material, especially ultrathin or nano-metric polymer films. The work investigates the engineering properties of freely standing polymer films deep in the glassy state with particular emphasis on yield behavior. Also, in freely standing films, a large modulus enhancement is observed and, recently, conflicting theoretical models of the stiffening behavior have appeared to explain the phenomenon. Such predictions are, of course important to nanomaterial design and use and the present work will establish the range of validity of these theories. Branched polymers have been shown to exhibit different nanoscale behavior from linear counterparts upon confinement on a supporting layer and the TTU bubble inflation method will be used to examine the effects of branching and unentangled polymer chain length on the viscoelastic properties of freely standing ultrathin films. Finally, it remains controversial whether or not the dynamics (relaxation time or viscosity) in glass-forming liquids, including polymers, diverge at a finite temperature. The PI's group has now demonstrated the first PVD ultrastable polymer glass that can be used to determine the upper bound relaxation times in a fashion similar to prior work with a 20 million year old amber but over a larger "window" of temperatures because the PVD polymer has a fictive temperature at least 50 K below the glass transition temperature, and optimization of the PVD conditions offers the possibility of an even larger testing window. Should the experiment be successful, it will provide further experimental data that can challenge theories of the behavior of glass-forming systems.

非技术摘要：为快速增长的纳米技术领域提供科学和工程解决方案的技术基础设施具有相当大的国家利益。 目前的工作探讨了构成相关启用技术基础的材料纳米限制行为的基本面。解决的一组重要问题与纳米厚的薄膜的工程特性（例如刚度和屈服强度）有关，这些薄膜是自由站立的形式，因此无法轻易测量。在此类材料中进行此类测量的唯一方法是PI实验室中开发的一种气泡通气方法，该方法允许测试极少量的材料，尤其是纳米薄的聚合物膜。该作品调查了在玻璃状状态深处自由地站立聚合物膜的工程特性，并特别着重于产量行为。这些研究将是第一个提供膜厚度和温度依赖性在自由地站立膜中的依赖性的研究。同样，在自由站立的膜中，观察到材料刚度的大大增强，最近，僵硬行为的理论模型似乎已经解释了这种现象。 这些预测对于纳米材料设计和使用至关重要，目前的工作将确定这些理论的有效性范围。也将研究分子结构效应。最后，纳米膨胀通货膨胀实验允许对以前由于其数量极少而无法实现的新型材料进行研究。在这种情况下，调查人员将研究由物理蒸气沉积（PVD）制造的超级聚合物玻璃杯，并且甚至比2000万年历史的琥珀色玻璃更稳定。这种高稳定性允许对一个长期的问题进行审问，该问题的解决方案是对眼镜理论的基础，尤其是如何长期对其在高级复合材料和粘合剂等重要领域的应用中的行为进行长期预测。 技术摘要：超薄聚合物膜的行为仍然是一个强烈的调查领域，但是大多数研究都限于底物支撑膜的情况，尽管研究表明在自由站立状态下会发生更大的影响。目前的工作使用TTU气泡通货膨胀方法对自由站立的超薄膜进行了三个方面，并利用该方法对极少数量的材料进行粘弹性测量的能力来研究由物理蒸气沉积（PVD）制造的超强聚合物玻璃的响应。解决的一组重要问题与工程特性有关，例如模量和纳米厚膜的屈服强度，这些薄膜是自由站立的形式，因此，不容易测量。在此类材料中进行此类测量的唯一方法是一种气泡通货膨胀方法，该方法允许测试极少量的材料，尤其是超薄或纳米 - 金属聚合物膜。该作品调查了在玻璃状状态深处自由地站立聚合物膜的工程特性，并特别着重于产量行为。同样，在自由站立的膜中，观察到大型模量增强，最近，僵硬行为的理论模型似乎已经解释了这种现象。 这些预测对于纳米材料设计和使用至关重要，目前的工作将确定这些理论的有效性范围。 已显示分支聚合物在支撑层上限制后表现出与线性对应物的不同纳米级行为，并且TTU气泡膨胀方法将用于检查分支和未进入的聚合物链长度对自由地站立超级薄膜的粘弹性特性的影响。最后，无论是否在包括聚合物在内的玻璃形成液体中的动力学（松弛时间或粘度），在有限的温度下散开，它仍然存在争议。 PI的小组现已展示了第一个PVD超强的聚合物玻璃，可用于确定上限放松时间的方式，类似于先前的工作，但具有2000万年历史的琥珀色，但温度更大的“窗口”，因为PVD聚合物具有至少在玻璃过渡温度下的虚拟温度，并且可以使PVD的条件达到较大的玻璃过渡温度，并提供了更大的窗口。如果实验成功，它将提供进一步的实验数据，以挑战玻璃形成系统行为的理论。