Electrocaloric Cooling in Polymers: Multi-Scale Modeling and Experimental Characterization

电热制冷：基于聚合物的传统技术替代品聚合物是一种长链状分子，由更小的单体组成。当聚合在一起时，这些聚合物链形成了一种重量轻、柔韧、易于制造且价格低廉的固体。当电场作用于某些聚合物固体时，它使单体旋转。这种旋转使材料的温度升高。去除电场使单体旋转回原来的位置，材料的温度降低。利用电场增加和降低温度的能力被称为电热效应。它在聚合物中的存在表明它们可以用来建造一个没有活动部件的制冷系统，这与在家庭、商业和工业应用中无处不在的蒸汽压缩循环非常不同。据估计，电热制冷的效率非常高。这项工作的目的是利用计算机建模和实验来了解聚合物中电热效应的起源。这项工作将为如何优化选择用于构建聚合物的单体和制造材料的理想条件提供指导。为了补充研究，将开发以下一代冷却技术为基础的推广活动，并向初高中学生展示。一门流体力学的本科机械工程课程将被翻转，即学生最初的学习在课堂外完成，课堂时间专门用于主动学习，学生通过解决问题、讨论和小组项目直接参与材料。本研究计划的目的是确定pvdf基聚合物薄膜的纳米结构和微观结构是如何驱动其电热冷却性能的。电热效应是一种现象，当对某些铁电材料施加或去除电场时，会发生与极化相关的温度和熵变化，导致内部单体偶极子旋转。在环境友好型聚合物中测量的大的电热效应指出了未开发的热管理应用潜力。原子计算、动力学蒙特卡罗模拟和实验表征工具将应用于构建从纳米到微米的长度尺度上的组成和结构如何促进电热效应的基本知识。具体来说，(i)将使用轻推弹性带方法计算来研究偶极子翻转事件的机制和能量学，（ii）将使用动力学蒙特卡罗模拟和实验表征来探索晶体和非晶态区域的微观结构与电热温度变化之间的关系。这些知识将为下一代冷却技术提供可能的冷却性能和实施策略。电热效应有可能在微观和宏观尺度上改变冷却和热管理。通过结合可扩展的制造、卓越的性能、廉价、丰富和轻质的材料，基于电的设备将与热电设备竞争，成为下一代固态冷却技术。

Electrocaloric Refrigeration: A Polymer-Based Alternative to Conventional TechnologiesA polymer is a long, chain-like molecule built from smaller components called monomers. When grouped together, these polymer chains form a solid that is light-weight, flexible, and easy and inexpensive to make. When an electric field is applied to some polymer solids, it makes the monomers rotate. This rotation causes the material's temperature to increase. Removing the electric field causes the monomers to rotate back to their original positions and the material's temperature decreases. The ability to increase and decrease temperature using an electric field is called the electrocaloric effect. Its presence in polymers indicates that they can be used to build a refrigeration system with no moving parts, very different from the vapor compression cycle that is ubiquitous in household, commercial, and industrial applications. Estimates suggest very high efficiency for electrocaloric refrigeration. The objective of this work is to use computer modeling and experiments to develop an understanding of the origin of the electrocaloric effect in polymers. The work will provide guidance in how to optimally select the monomers used to build the polymers and the ideal conditions for making the materials. To complement the research, outreach activities based on next-generation cooling technologies will be developed and presented to middle-school and high-school students. An undergraduate mechanical engineering course in fluid mechanics will be flipped, whereby the initial student learning is done outside the classroom and class time is devoted to active learning, where students engage directly with the material through problem solving, discussion, and small group projects.The objective of this research program is to determine how the nanostructure and microstructure of PVDF-based polymer thin films drive their electrocaloric cooling performance The electrocaloric effect is a phenomenon in which polarization-related temperature and entropy changes occur when an electric field is applied/removed from certain ferroelectric materials, causing the rotation of internal monomer dipoles. The large electrocaloric effect measured in environment-friendly polymers points to untapped potential for application to thermal management. Atomistic calculations, kinetic Monte Carlo simulations, and experimental characterization tools will be applied to build fundamental knowledge of how composition and structure across length scales from nanometers to microns contribute to the electrocaloric effect. Specifically, (i) the mechanisms and energetics of the dipole flipping events will be investigated using nudged elastic band method calculations, and (ii) the correlation between the microstructure of the crystalline and amorphous regions to the electrocaloric temperature change will be explored using kinetic Monte Carlo simulations and experimental characterization. This knowledge will inform what cooling performance is possible and strategies for implementation into next-generation cooling technologies. The electrocaloric effect has the potential to transform cooling and thermal management at micro and macro scales. By combining scalable manufacturing, excellent performance, and inexpensive, abundant, and light-weight materials, electrocaloric-based devices will rival thermoelectrics as a next-generation solid-state cooling technology.