Seriography‐Guided Reduction of Graphene Oxide Biopapers for Wearable Sensory Electronics

Abstract

Novel nacre-mimic bionanocomposites, such as graphene-based laminates, are pushing the boundaries of strength and toughness as flexible engineering materials. Translating these material advances to functional flexible electronics requires methods for generating print-scalable microcircuits (conductive elements surrounded by dielectric elements) into these strong, tough, lightweight bionanocomposites. Here, we present a new paradigm for printing flexible electronics by employing facile, eco-friendly seriography to confine the reduction of graphene oxide biopapers This article is protected by copyright. All rights reserved.2 reinforced by silk interlayers to be strong and chemically-resilient. Well-defined, micro-patterned regions on the biopaper are chemically reduced, generating a 10 6 increase in conductivity (up to 10 4 S/m) in order to facilitate sensing electronic functionalities. We showcase flexible, robust graphenesilk circuits in diverse, prospective applications as resistive moisture sensors and capacitive proximity sensors. Unlike electronics generated from the printing conductive inks on substrates, seriographyguided reduction does not create mechanically weak interfaces between dissimilar materials, and do not require the judicious formulation of conductive (i.e. graphene-or Ag nanoparticle-loaded) inks. We demonstrate the unimpaired functionality of printed-in graphene-silk microcircuits after thousands of punitive folding cycles, and chemical attack by harsh solvents, hazardous conditions which usually ruin existing materials designs. This novel approach provides a low-cost, portable solution for printing micron-scale conductive features uniformly across large areas (>hundreds of cm 2 ) in layered composites for emerging applications including wearable health monitors, functional electronic skin, as well as large-scale rollable antennas and conformable displays.

UV Laser‐Induced Polyimide‐to‐Graphene Conversion: Modeling, Fabrication, and Application

“…Correspondingly, the properties of the rGO-based one shown in the report are response distance 20 mm, linearity ≈0.98, and sensitivity 0.1080 V mm −1 . [45] The sensitivity is defined as the slope value of the potential response to the distance between the sensor and the human hand. Figure 8a,b shows the response/recovery when a human hand was approaching or moving away from the sensors, respectively.…”

“…Compared with the rGO‐based one, the LIG‐based proximity sensor shows superior properties, such as larger response distance (50 mm), better linearity(≈0.99), and higher sensitivity (0.2083 V mm −1 , the sensitivity is defined as the slope value of the Log potential response to the distance between the sensor and the human hand). Correspondingly, the properties of the rGO‐based one shown in the report are response distance 20 mm, linearity ≈0.98, and sensitivity 0.1080 V mm −1 . The sensitivity is defined as the slope value of the potential response to the distance between the sensor and the human hand.…”

“…After the LIG electrodes are formed, the un‐converted PI film acts as a dielectric layer between the two electrodes. When the object, such as a human hand, approaches, the charge distribution on the graphene electrodes is correspondingly altered by the surface charge on human skin, resulting in a change in the capacitance . Thus, the motion of close‐by objects can be detected by characterizing the capacitance variation.…”

Robust and Flexible Micropatterned Electrodes and Micro‐Supercapacitors in Graphene–Silk Biopapers

“…For instance, in shadow masking flash lithography, separation between mask, and GO‐based substrate creates broad drop‐off of reducing radiation intensity; while in stamping, asperities may block contact in surrounding loci to the reductant . While screen printing can create conformal contact between reductant and GO composite surface, the deposited reductant may deform due prior to and during firing to fix the reductant paste shape …”

“…The structure of GO consists of a monolayer hexagonal network of sp 2 hybridized carbon interspersed with sp 3 carbon bearing oxygen‐containing functional groups, with hydroxyl and epoxy groups at the basal plane, and carboxy and carbonyl groups at sheet edges . The removal of these oxygenated groups via reduction processes can produce an increase in conductivity by several orders of magnitude (up to 10 4 S m −1 in graphene oxide–silk fibroin, GO–SF, composites), opening a route toward applications in flexible energy storage . Much work has also focused on the assembly of nanocomposites, whereby GO acts as 2D “bricks” bound by 1D polymeric binders to yield nacre‐like structures designed for superior mechanical properties, including extreme tensile strength (526.7 MPa in GO–chitosan), Young's modulus, toughness (13.9 MJ m −3 reduced graphene oxide–silk fibroin, GO–SF), and stretchability (up to 10.1% in GO–polyvinyl alcohol) .…”