Abstract
Conductive hydrogels are an ideal bio-integrated soft material and show great potential in soft sensors. However, it remains a great challenge to develop an integrated conductive gel combining excellent environmental stability and mechanical properties. Herein, we synthesize a transparent, self-adhesive conductive organohydrogel with excellent environmental stability and UV-blocking performance by constructing multiple cross-links between tannic acid, polyacrylamide, and polyvinyl alcohol. The addition of vinyl hybrid silica nanoparticles can promote dynamic cross-linking of polymer networks and endow organohydrogels with superior mechanical performance (>1800%, 320 kPa). Concurrently, the binary solvent system comprising water and ethylene glycol enables organohydrogels to accommodate different application environments (from −40 °C to 40 °C). Notably, with the incorporation of tannic acid, organohydrogels exhibit lasting and repeatable adhesion (80 kPa), as well as good UV-blocking (>90%). Furthermore, these conductive organohydrogels with great strain sensitivity were used as strain sensors to monitor and distinguish large movements (soft robot movements) and subtle human movements (smiling and electrocardiograph signal) at different temperatures. The conductive organohydrogels have great potential in healthcare monitoring and smart wearable soft electronic devices.
Highlights
Conductive hydrogels are a desired material for soft sensors owing to their soft touch,1 skin-friendliness,2 and excellent conductivity.3 To satisfy the aesthetic and visual requirements of application to the skin surface, transparency is an important requirement for soft electronics.4–7 a majority of traditional conductive hydrogels are non-transparent because they comprise opaque conducting polymers, such as carbon-based nanomaterials or metal nanoparticles (Au and Ag).8–12 Conductive hydrogels with high transparency are generally and effectively produced by adding salt materials.13–15 the stability of these ionic gels is poor, especially in extreme environments: low temperature leads to freezing of the gels, while high temperature causes the gels to dry
The strain sensitivity of the organohydrogel sensor was estimated by a gauge factor (GF), which was a parameter defined as the ratio of the change in relative resistance to the applied strain (α), where R0 and R are the original resistance without exerting strain and the resistance after applied strain, respectively, GF = [(R − R0)/R0]/α
All the important bands for PAM appeared in the hydrogel PAM/vinyl hybrid silica nanoparticles (VSNPs), which was formed by free radical polymerization by using VSNP as the cross-linking agent
Summary
Conductive hydrogels are a desired material for soft sensors owing to their soft touch, skin-friendliness, and excellent conductivity. To satisfy the aesthetic and visual requirements of application to the skin surface, transparency is an important requirement for soft electronics. a majority of traditional conductive hydrogels are non-transparent because they comprise opaque conducting polymers, such as carbon-based nanomaterials (carbon nanotubes and graphene) or metal nanoparticles (Au and Ag). Conductive hydrogels with high transparency are generally and effectively produced by adding salt materials (lithium chloride and potassium chloride). the stability of these ionic gels is poor, especially in extreme environments: low temperature leads to freezing of the gels, while high temperature causes the gels to dry. Mussel-inspired polydopamine (PDA) is a possible sticky material, which can endow ionic gels with excellent adhesion to different surfaces.. It is easy to monitor different human movements or shape change by directly sticking the self-adhesive hydrogels with PDA particles to the skin or a soft robot, which makes the sensing property of ionic gels stable and reproducible.. Inspired by natural mussel chemistry, we proposed a facile method to prepare a flexible, transparent, and sticky organohydrogel with high environmental stability and an external UV blocking property. In this hybrid organohydrogel system, acrylamide (AM). Organohydrogels proposed in this research may be perfect candidates for bionic electronic skin and strain sensors of soft robot applications
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