Piezoresistive and Electrical Properties of a Catecholic Amino Acid–Polyacrylamide Single-Walled Carbon Nanotube Hydrogel Hybrid Network

Abstract

We have developed a functional hydrogel combining the advantages of single-walled carbon nanotube (SWCNT) hydrogels and 3,4-dihydroxy-l-phenylalanine (l-DOPA) that would be expected to lead to a material with elevated piezoresistive ability. SWCNT hydrogel precursors were thus embedded into the catecholic amino acid 3,4-dihydroxy-l-phenylalanine–polyacrylamide (l-DOPA-PAM) hydrogel to form a l-DOPA-PAM-SWCNT hydrogel hybrid network. This hybrid network as formed was soft but became a hard gel at room temperature. An advantage of this material design is the prevention of overoxidation of l-DOPA to maintain enough free catechol groups to endow the desired properties. Several characterization techniques, including optical microscopy, field-emission scanning electron microscopy, Raman spectroscopy, and dynamic mechanical analysis, were utilized to characterize the l-DOPA-PAM-SWCNT hydrogel hybrid network. The negative piezoresistive effect and electrical properties of the l-DOPA-PAM hydrogel and the l-DOPA-PAM-SWCNT hydrogel hybrid network were measured under different pressures and at different times after the application of pressure started, demonstrating the potential for pressure-sensing applications.

Flexible Strain-Sensitive Sensors Assembled from Mussel-inspired Hydrogel with Tunable Mechanical Properties and Wide Temperature Tolerance in Multiple Application Scenarios

“…Due to the Zr 4+ can react with the carboxyl groups of PAA- g -Dopa to form stable metal coordination at room temperature, the mechanical properties of hydrogels can be controlled by Zr 4+ . Over the past decade of research, researchers have found that the catechol group of Dopa is a key component in adhesion processes. , As shown in Scheme (c), the catechol groups of PAA- g -Dopa enable stick to the various substrates through a range of interactions, including hydrogen bonding, metal coordination, hydrophobic interaction, and other interaction (e.g., π–π electron or cation-π interaction). In detail, for inorganic surfaces, catechol groups could form hydrogen bonds, , p–p electro interaction, and metal–Dopa coordinate bonds .…”

Stimuli-Responsive Polymer Networks: Application, Design, and Computational Exploration

“…22,128−131 For a mechanical response, in one study, a hybrid network was fabricated combining a single-walled carbon nanotube (SWCNT) hydrogel and a 3,4-dihydroxy-L-phenylalaninepolyacrylamide hydrogel (L-DOPA-PAM). 132 This material has possible utility in pressure sensing applications due to its negative piezoresistive effect, meaning an increase in the stress applied to the material decreases its electrical resistance. Its electrical resistance also decreased over time at a constant applied pressure.…”

Hydrogel-Based Energy Harvesters and Self-Powered Sensors for Wearable Applications

“…Furthermore, the piezoresistive effect typically refers to the phenomenon where the resistance of a semiconductor changes due to the variation in energy levels of the conduction band caused by stress-induced band structure changes [101][102][103][104]. However, in the context of hydrogel applications, the piezoresistive effect generally refers to changes in resistance resulting from variations in the dimensions of the gel under deformation [105][106][107][108]. Based on this characteristic, hydrogels can be used for stress or strain sensing.…”