Highly sensitive and self-healing conductive hydrogels fabricated from cationic cellulose nanofiber-dispersed liquid metal for strain sensors

Abstract

The emergence of liquid metal (LM) emulsion as a soft multifunctional filler brings a new opportunity for fabricating hydrogel-based strain sensors with multifunctional properties. However, the extremely large surface tension and high density of LMs inhibit emulsification. Herein, we demonstrated a strategy for stabilizing LM emulsions using cationic cellulose nanofibers (CCNFs) to encapsulate LM droplets through strong electrostatic attraction with LM. By inducing acrylic acid (AA) polymerization in the presence of a CCNF-stabilized LM emulsion, a conductive hydrogel was prepared with the formation of reversible hydrogen bonds, ionic coordination, and electrostatic interactions among CCNFs, LM droplets, and poly(acrylic acid) (PAA). The hydrogel obtained, named the CCNF-LM-PAA hydrogel, shows good conductivity (1.54 S m −1 ), remarkable tensile strength and elongation at break, self-adhesiveness, and quick self-healing capability. As a strain-sensing material, the CCNF-LM-PAA hydrogel exhibits a very high sensing sensitivity (gauge factor = 16.2), a low strain detection limit (less than 1%), a short response/recovery time (107/91 ms), and good durability (300 cycles). These results enable the CCNF-LM-PAA hydrogel-based strain sensor to be an excellent wearable device for monitoring various human activities. Therefore, introducing additional electrostatic interactions by using CCNFs to stabilize LM emulsions provides a practical way to enhance the strain-sensing performance of LM emulsion-based hydrogels for assembling selfattached wearable devices.

Functional conductive hydrogels: from performance to flexible sensor applications

“…Recently, it was reported that the high surface tension of liquid metals is solved by using cationic cellulose nanofibers (CCNFs) to prepare a conductive hydrogel (CCNFs-LM-PAA) with excellent electrical conductivity. 61 Hydrogen bonding and electrostatic interaction between CCNFs and Ga prevent precipitation or aggregation. With the increase of Ga, the maximum strain decreases and the maximum stress increases, but the conductivity of the hydrogel is not significantly affected, and finally a conductivity of 1.54 S m −1 is achieved.…”

Electrically Conductive AgNPs/TPU-Electrospun Fibers with Hierarchical Microstructures by a One-Step Method for a High-Performance Flexible Pressure Sensor

“…Flexible pressure sensors typically consist of a flexible substrate, active materials, and electrodes . Commonly used flexible substrate materials include polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), and poly(acrylic acid) hydrogel . Among them, the electrospun TPU nanofiber film has the advantages of high porosity, large surface area, and good air permeability, making it a candidate material for flexible substrates.…”

Establishing a Corrugated Carbon Network with a Crack Structure in a Hydrogel for Improving Sensing Performance

“…They can perfectly adapt to soft human skin because of their high similarity with soft biological tissues . To date, many hydrophilic polymers and conductive materials have been used to fabricate conductive hydrogels with various compositions and structures by directly mixing them before inducing the gelatinization of the polymers. − Because sensing performance and self-healing and mechanical properties always determine the reliability and lifetime of strain sensors in related applications, , the development of self-healing conductive hydrogels with high sensing performance and good toughness is highly desirable. Moreover, the adhesiveness is also important for the application of hydrogel-based strain sensors.…”