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，突出了可拉伸导体的巨大挑战：电子设备通常由坚硬的材料制成，而生物组织则是超级柔软、可拉伸和坚韧的。该奖项支持基础研究，以阐明液体金属填料如何同时作为弹性体基体的软化剂、增韧剂和导电性增强剂，以实现极其柔软、可拉伸、超坚韧和高导电性的导体。从这个项目中获得的见解可能会带来更好的设计，新颖的设备，提高可穿戴和可拉伸电子产品的可靠性，从而促进国家的健康和繁荣。此外，该项目将在多学科环境中培养多样化的学生群体，并加强少数民族对科学和工程的参与，特别是在宾夕法尼亚州立大学，特别是在可拉伸电子的力学和材料方面。对于现有的工程材料，柔韧性和导电性似乎是两个相互冲突的材料特性；改善一方必然会损害另一方。特别是，电导率往往随着机械拉伸而下降。为了克服这些限制，本项目旨在制造液态金属-弹性体复合材料，并阐明液态金属填料在弹性体基体中的软化、增韧和导电机制的作用。本文建立的多尺度模型由在液态金属表面自发生长的纳米厚氧化层的原子模拟、液态金属填料的不可压缩性和弹性体基体的超弹性的新处理组成。通过不同长度尺度的实验表征，系统地验证了模型对材料性能的预测。综合实验建模方法对复合材料的低模量、高拉伸性、优异的可恢复性、超韧性和拉伸增强导电性提供了深入的见解。这种深入的理解将为优化液态金属-弹性体复合材料的尺寸、形态和液态金属填料的体积分数提供指导，并将有助于促进其他性能更好的可拉伸导体设计的变革进展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.