Carnegie Mellon University
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Soft, Stretchable, and Conductive Hydrogel Composites

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thesis
posted on 2023-03-08, 18:43 authored by Yunsik Ohm

Hydrogels, crosslinked polymeric networks mostly filled with water, have unique mechanical properties, including extreme compliance, stretchability, and conformability. However, their intrinsic ionic conductivity (10−5 to 10−1 S cm−1) limits their use in soft electronics, wearable technologies, or bioelectronics. One way to improve their electrical properties is to introduce conductive fillers into a soft hydrogel matrix. In turn, the high concentrations of metallic fillers required to achieve adequate conductivity for digital circuit applications degrade hydrogel’s desirable mechanical properties. To overcome this limitation, we need a new material architecture that maintains the soft (< 102 kPa) and stretchable (> 50% strain) properties of hydrogels while also enabling high electrical conductivity (> 100 S cm−1). 

This dissertation introduces various soft conductive composites that achieve low electrical resistance through percolating networks of embedded silver particles. Most of this work focuses on a novel material architecture and a processing method in which silver flakes are suspended with a tough hydrogel. By controlling the water content inside, the composite functions as either a conductor or an insulator. Moreover, this property is reversible so that it can reconfigure the conductive pathways within the composite. Overall, this dissertation contributes to the diversity of hydrogel-based conductors for soft and stretchable electronics. 

History

Date

2022-06-17

Degree Type

  • Dissertation

Department

  • Mechanical Engineering

Degree Name

  • Doctor of Philosophy (PhD)

Advisor(s)

Carmel Majidi