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.
