Active Regulation of Thermal Boundary Conductance

分子尺度的模拟表明，当对电活性聚合物施加电场时，它会使其收缩，并使其在机械上变得更硬。结果，聚合物的导热系数提高了40%。同样，当聚合物附着在金属基板上时，其作用是施加电场，粘附力被增强，模拟预测通过该界面的导热系数增加了六倍。因此，我们可以通过在两层金属薄膜之间夹上一层电活性聚合物薄膜来设计一个热阀，然后根据薄膜的厚度对这些金属薄膜施加几十伏的电压，就可以将这种多层结构的热流速率改变三到四倍。本项目的目的是通过实验证明这种热流转换机制，清楚地阐明其潜在的物理原理，并在此基础上改进材料设计，例如通过创建具有更大变形幅度的分子键合聚合物和陶瓷组件的纳米多孔结构，从而实现更大的热流放大比。这项研究的预期结果是一项应用于许多需要热管理的情况的技术，包括在有限环境中调节热流，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，即允许控制热流方向的设备。研究结果可能会激发诸如用于控制选择性过滤的驱动膜、具有时间差采样能力的传感器、用于靶向药物和热输送的可展开医疗设备（例如用于局部癌症治疗）等技术。最后，本文采用的研究策略可能会通过验证新兴的研究模拟指导方法和展示创新的材料开发方法来影响特定学科以外的科学和技术。本研究的目标是探索新的纳米结构材料设计，允许在界面和表面的热传递特性的原位调节，即在极端的传热水平之间切换或在该范围内连续调整热导。这种功能响应是通过优化电活性聚合物的结构和拓扑结构来实现的，这些聚合物被整合到致密的纳米多孔杂化材料中，即有机和无机成分在分子水平上分散并相互化学结合，从而最有效地利用它们的固有特性。为了实现这一目标，计算被用来探索控制材料行为的基本原理，并确定目标功能响应的最有效的分子构型。由此获得的设计原则指导了材料的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了验证。首先，从基于分子模拟的概念验证研究中得出的基础材料设计概念，预测当对沉积在金属基板上的超薄压电聚合物层施加电场时，导热系数将达到40%，热边界导热系数将增加6倍，并通过实验验证，并确定了潜在的机制。从这些见解，设计蓝图的材料设计产生最大的热输运调节行为被导出。因此，纳米多孔聚合物-无机杂化材料作为一种材料，由于其在压电驱动下的大应变，可能会产生更大的热传递特性变化。相反，在专门设计的纳米多孔结构中，研究了大振幅驱动作为可调节膜的应用，用于选择性过滤、检测病原体、时间选择性采样、靶向药物递送和流体流动调节。

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.