Multifunctional Poly(vinyl alcohol) Nanocomposite Organohydrogel for Flexible Strain and Temperature Sensor

Abstract

Hydrogels are important for stretchable and wearable multifunctional sensors, but their application is limited by their low mechanical strength and poor long-term stability. Herein, a conductive organohydrogel with a 3D honeycomb structure was prepared by integrating carbon nanotubes (CNTs) and carbon black (CB) into a poly­(vinyl alcohol)/glycerol (PVA/Gly) organohydrogel. Such a nanocomposite organohydrogel is built on a physical cross-linking network formed by the hydrogen bonds among PVA, glycerol, and water. CNTs and CB had an add-in synergistic impact on the mechanical and electrical performances of the PVA/Gly organohydrogel because of the distinct aspect ratios and geometric shapes. The prepared organohydrogel integrated with a tensile strength of 4.8 MPa, a toughness of 15.93 MJ m–3, and flexibility with an elongation at break up to 640%. The organohydrogels also showed good antifreezing feature, long-term moisture retention, self-healing, and thermoplasticity. Sensors designed from these organohydrogels displayed high stretching sensitivity to tensile strain and temperature, with a gauge factor of 2.1 within a relatively broad strain range (up to ∼600% strain), a temperature coefficient of resistance of −0.935%·°C–1, and long-term durability. The sensors could detect full-range human physiological signals and respond to the change in temperature, which are highly desired for multifunctional wearable electronic devices.

Environmentally Compatible Wearable Electronics Based on Ionically Conductive Organohydrogels for Health Monitoring with Thermal Compatibility, Anti‐Dehydration, and Underwater Adhesion

“…Besides, we observe that the organohydrogel‐based strain sensor could respond within 116 ms and recover within 68 ms (Figure 5c), which is faster than many other organohydrogel‐based strain sensors. [ 32,47–49 ]…”

Highly Sensitive On‐Skin Temperature Sensors Based on Biocompatible Hydrogels with Thermoresponsive Transparency and Resistivity

“…This −0.0289°C −1 sensitivity value was found to be several times higher than previously reported values using other hydrogels displaying intrinsic conductivity and similar to those using hydrogels with ionic additives or volume changes (Table S1, Supporting Information). [11][12][13][14][15][16][17][18]24,25] The temperature sensor of TRH 1-1 showed a reversible change in resistance under temperature cycles with no significant hysteresis, as shown in Figure S9 (Supporting Information) (less than 1% change in resistance corresponding to each temperature during heating and cooling).…”

“…[10] Numerous previous works have been devoted to fabricating wearable temperature sensors based on hydrogels that can vary their electrical resistance as a result of changes in ion conductivity [11][12][13][14][15]24,25] or volume due to swelling/contraction with temperature. [16][17][18] Thermoresponsive hydrogels (TRHs) have played a crucial role in a variety of temperature-adaptive applications for actuators, [19] membranes, [20] displays, [21] and electrolytes [22] due to their intelligent thermo-responsive transitions. TRHs are classified by the two types of volume transition that they can undergo the lower critical solution temperature (LCST) or the upper critical solution temperature (UCST).…”

“…[ 10 ] Numerous previous works have been devoted to fabricating wearable temperature sensors based on hydrogels that can vary their electrical resistance as a result of changes in ion conductivity [ 11–15,24,25 ] or volume due to swelling/contraction with temperature. [ 16–18 ]…”

Recent Progress in Essential Functions of Soft Electronic Skin

“…However, it has been reported that the ion conductivity will be enhanced with the increase of temperature due to the increase of ion mobility. [204,205] Therefore, ionic hydrogels [33,119,[206][207][208] and ionogels [107,209] can also be designed into soft temperature sensors. For instance, Zhang et al [206] fabricated the dopamine-triggered gelation (DTG) conductive hydrogels, which exhibited unique thermoresponsive property.…”