Skin-Inspired Mechanics of Liquid Metal - Elastomer Composites as Super Soft, Stretchable, and Tough Conductors

可穿戴电子领域的出现，以及它在生物医学设备和软机器人中的应用，突显了可伸缩导体的一个巨大挑战：电子设备通常由硬材料制成，而生物组织超级柔软、可伸展和坚韧。该奖项支持基础研究，以阐明液态金属填充剂如何同时充当弹性体基质的软化剂、增韧剂和电导增强剂，以实现极软可伸缩、超韧和高导电性的导体。来自该项目的见解可能会导致可穿戴和可伸缩电子产品的更好设计、新设备和更高的可靠性，从而促进国家健康和繁荣。此外，该项目将在多学科背景下培训不同的学生群体，并加强少数群体对科学和工程以及可拉伸电子设备的机械和材料的参与，特别是在宾夕法尼亚州立大学。对于现有的工程材料来说，柔性和导电性似乎是两个相互冲突的材料特性；改善其中一个必然会损害另一个。特别是，电导率经常随着机械拉伸而降低。为了克服这些限制，本项目旨在制备液态金属-弹性体复合材料，并阐明液态金属填充物在弹性体基质中的软化、增韧和导电机制中的作用。本文开发的多尺度模型包括对液态金属表面自发生长的纳米厚氧化层的原子模拟，对液态金属填充物不可压缩的新处理，以及弹性体基质的超弹性。通过不同长度尺度下的实验表征，系统地验证了材料性能的建模预测。实验-建模一体化的方法使人们对复合材料的低弹性、高伸长性、优异的可恢复性、超韧性和拉伸增强的导电性有了深刻的了解。这种深入的理解将为液态金属-弹性体复合材料在液态金属填充物的尺寸、形态和体积分数方面的优化提供指导，并将有助于促进其他具有更高性能的可拉伸导体设计的变革性进展。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The emergence of the field of wearable electronics, along with its applications in biomedical devices and soft robotics, has highlighted a grand challenge in stretchable conductors: electronic devices are usually made of hard materials, whereas biological tissues are super soft, stretchable, and tough. This award supports fundamental research to elucidate how liquid-metal fillers simultaneously act as a softener, a toughener, and a conductance enhancer for the elastomer matrix to realize extremely soft and stretchable, super tough, and highly conductive conductors. Insights from this project will potentially result in better design, novel devices, and improved reliability of wearable and stretchable electronics, and therefore advance the national health and prosperity. Further, the project will train a diverse group of students in a multidisciplinary setting and enhance minority involvement and participation in science and engineering in general and in mechanics and materials of stretchable electronics in particular at Penn State. For existing engineering materials, flexibility and conductivity appear to be two conflicting material properties; improving one necessarily compromises the other. In particular, electrical conductivity often degrades with mechanical stretch. To overcome these limitations, this project aims to fabricate liquid metal-elastomer composites and elucidate the role of liquid metal fillers on the softening, toughening, and conducting mechanisms in elastomer matrices. The multiscale model developed herein is composed of atomistic simulations of the nano-thick oxide layer spontaneously grown on the liquid metal surface, novel treatment of the incompressibility of the liquid metal fillers, and hyper-elasticity of the elastomer matrix. The modeling predictions of the material properties are systematically validated by experimental characterizations at different length scales. The integrated experimental-modeling approach offers deep insights into the low modulus, high stretchability, excellent recoverability, super toughness, and stretching-enhanced conductivity of the composites. Such an in-depth understanding will provide guidance to optimize the liquid metal-elastomer composites in terms of the size, morphology, and volume fraction of the liquid-metal fillers, and will help foster transformative progress in the design of other stretchable conductors with improved performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.