Active Regulation of Thermal Boundary Conductance

CBET-1402845 Kieffer（密歇根大学，安阿伯）分子尺度模拟已经表明，当向电活性聚合物施加电场时，它会导致它收缩，并且它在机械上变得更硬。 因此，聚合物的导热率增加了高达40%。 类似地，当聚合物粘附到用于施加场的金属基底上时，粘附力被加强，并且模拟预测跨该界面的热导率增加了六倍。 因此，可以通过在两个金属膜之间夹一个薄的电活性聚合物膜来设计一个热阀，并且通过向这些金属膜施加几十伏电压，取决于膜的厚度，可以将穿过该多层结构的热流率改变三到四倍。 该项目的目标是通过实验证明这种热流切换机制，以清楚地阐明潜在的物理原理，并基于这些见解，改进材料设计，例如通过创建分子结合的聚合物和陶瓷组件的纳米多孔结构，表现出更大的变形幅度，从而实现更大的热流放大率。 这项研究的预期成果是一项技术，可应用于许多需要热管理的情况，包括调节受限环境中的热流，例如，生物体、发动机、燃料电池、传感器和化学反应器，甚至热二极管，即，可以控制热流方向的装置。 这些研究结果可能会激发一些技术，如用于受控选择性过滤的致动膜，具有时间差采样能力的传感器，用于靶向药物和热量输送的可部署医疗设备，例如，用于局部癌症治疗。 最后，通过验证新兴的研究模拟引导方法和展示创新的材料开发方法，本文采用的研究策略可能会影响特定学科以外的科学和技术。本研究的目标是探索新型纳米结构材料设计，允许在界面和表面原位调节热传输性能，即，在热传递的极端水平之间切换或在该范围内连续调节热导。 这种功能响应是通过优化掺入到致密和纳米多孔混合材料中的电活性聚合物的结构和拓扑来实现的，即，其中有机和无机组分在分子水平上分散并彼此化学键合，以便最有效地利用它们的固有性质。 为了实现这一目标，计算用于探索支配材料行为的基本原理，并确定针对目标功能响应的最有效分子构型。 所获得的设计原则指导材料开发和适当的化学合成路线，并通过表征所得材料的介电，机械和热传输行为进行验证。 首先，实验验证了底层材料设计概念，该概念来自基于分子模拟的概念验证研究，预测当向沉积在金属基板上的压电聚合物超薄层施加电场时，热导率增加40%，热边界电导增加6倍，并确定了底层机制。 从这些见解，蓝图的材料设计，产生最大的热传输调节行为的设计。 因此，纳米多孔聚合物-无机杂化材料被探索为由于其响应于压电致动的大应变而可能产生热传输性质的放大变化的材料。 相反，在专门设计的纳米多孔结构的大幅度驱动的应用程序进行了研究，作为可调膜的选择性过滤，病原体的检测，时间选择性采样，有针对性的药物输送，和流体流量调节。

CBET-1402845Kieffer (Univ. of Michigan, Ann Arbor)Molecular-scale simulations have shown that when applying an electric field to an electro-active polymer it causes it to constrict and it becomes mechanically stiffer. As a result, the thermal conductivity of the polymer increases by up to 40%. Similarly, when the polymer adheres to a metallic substrate, which serves to apply the field, the adhesive forces are intensified and simulations predict that the heat conductance across this interface increases by a factor of six. Accordingly, one can devise a heat valve by sandwiching a thin electro-active polymer film between two metallic films, and by applying a few tens of volts to these metal films, depending on film thickness, one can turn alter the heat flow rate across this multi-layered structure by a factor of three to four. The objective of this project is to demonstrate this heat flow switching mechanism experimentally, to clearly elucidate the underlying physical principles, and based on these insights, to improve the materials design, for example by creating nano-porous structures of molecularly bonded polymer and ceramic components that exhibit larger deformation amplitudes, so as to achieve bigger heat flow amplification ratios. The expected outcome of this research is a technology with application in numerous situations that require thermal management, including regulating heat flow in confined environments, e.g., living organisms, engines, fuel cells, sensors, and chemical reactors, and even thermal diodes, i.e., devices that allow one to control the direction of heat flow. The research findings may inspire technologies such as actuated membranes for controlled selective filtering, sensors with time-differential sampling capability, deployable medical devices for targeted drug and heat delivery, e.g., for localized cancer treatment. Finally, the research strategy employed here may impact science and technology beyond a specific discipline by validating an emerging research simulation-guided approach and by demonstrating an innovative materials development approach.The goal of this research is to explore novel nano-structural materials designs that allow for the in situ regulation of thermal transport properties at interfaces and surfaces, i.e., switching between extreme levels of heat transfer or continuously adjusting the thermal conductance within that range. This functional response is achieved by optimizing the structure and topology of electro-active polymers incorporated into dense and nano-porous hybrid materials, i.e., in which the organic and inorganic components are dispersed at the molecular level and chemically bonded to one another, so as to make most efficient use of their inherent properties. To accomplish this goal computation is used to explore the fundamental principles that govern materials behavior and determine the most effective molecular configurations for the targeted functional response. The design principles so obtained guide materials development and appropriate chemical synthesis routes, and are validated by characterizing the dielectric, mechanical, and thermal transport behavior of the resulting materials. First, the underling materials design concepts, which ensues from a molecular simulation-based proof-of-concept study, predicting a 40% thermal conductivity and a six-fold thermal boundary conductance increase when applying an electric field to an ultra-thin layer of piezoelectric polymer deposited on a metal substrate, is verified experimentally and the underlying mechanisms are identified. From these insights, blueprints for the design of materials design that yields maximal thermal transport regulating behavior are derived. Accordingly, nano-porous polymer-inorganic hybrid materials are explored as materials that potentially yield magnified changes in thermal transport properties because of their large strains in response to piezoelectric actuation. Conversely, large-amplitude actuation in purposely designed nano-porous structures are investigated for application as adjustable membranes for selective filtration, detection of pathogens, time-selective sampling, targeted drug delivery, and fluid flow regulation.