Large Scale Continuous Layer-by-Layer Assembly of Paper-based Nanocomposites for High Fidelity Multifunctional Sensors

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Paper is a ubiquitous material invented in ancient China comprising cellulose fibers tangled and twisted with each other forming a porous network. Today?s ever-digitalized world has spurred new interests in paper as a low-cost, sustainable, flexible, lightweight and biocompatible platform for portable electronics. This project will provide the framework for the incorporation of nanomaterials, such as carbon nanotubes (CNTs) and cellulose nanofibrils (CNFs), into fibrous networks, with the goal of enabling easy scale-up manufacturing of paper-based nanocomposites (PBC). The grant provides fundamental knowledge for the development of a continuous layer-by-layer assembly process, mimicking industrial papermaking, to manufacture strain sensors with electrical conductivity, enhanced strength and high sensitivity to external stimuli for multifunctional sensing applications. This novel process has the potential to reinvigorate the pulp and paper industry and benefit the U.S. economy and promote the progress of science by changing the way smart materials and electronic devices are manufactured and used for applications such as wearable devices, healthcare applications, structural monitoring systems, soft robotics, and electronic skins. The interdisciplinary approach encourages the participation of diverse individuals including women and underrepresented minority groups in engineering research and education. The layer-by-layer assembly of paper-based nanocomposites in a continuous web former can overcome several limitations existing multifunctional sensors have, ranging from cost, flexibility, durability, and mechanosensitivity. This fundamental study is to fill the knowledge gaps on interface tailoring for the incorporation of well-dispersed nanoparticles at high content into auxetic fiber networks, and on microcrack-assisted manipulation to control the disconnection-reconnection of percolated conductive structures in paper-based nanocomposites. Auxetic paper nanocomposites possess a negative Poisson's ratio, meaning they expand biaxially during stretching, in direct contrast to conventional materials, which endure transverse Poisson compression under tension. Bidirectional expansions in auxetic materials contribute to moving electrically conductive nanoparticles away from one another, thereby improving the sensitivity of stretchable resistive sensors. Numerical simulations are performed to understand the coupling between mechanical motion and electron transport in auxetic materials, while experimental research is conducted to verify the model, test the hypothesis that structural Poisson's ratio and strain concentration can be tailored to achieve ultrahigh mechanosensitivity, and establish process-structure-property relationships in paper-based multifunctional sensors.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.