Stimulus-responsive hydrogels are of great significance in soft robotics, wearable electronic devices, and sensors. Near-infrared (NIR) light is considered an ideal stimulus as it can trigger the response behavior remotely and precisely. In this work, a smart flexible stimuli-responsive hydrogel with excellent photothermal property and decent conductivity are prepared by incorporating MXene nanosheets into the physically cross-linked poly(N-isopropyl acrylamide) hydrogel matrix. Because of outstanding photothermal effect and dispersion of MXene, the composite hydrogel exhibits rapid photothermal responsiveness and excellent photothermal stability under the NIR irradiation. Furthermore, the anisotropic bilayer hydrogel actuator shows fast and controllable light-driven bending behavior, which can be used as a light-controlled soft manipulator. Meanwhile, the hydrogel sensor exhibits cycling stability and good durability in detecting various deformation and real-time human activities. Therefore, the present study involving the fabrication of MXene nanocomposite hydrogels for potential applications in remotely controlled actuator and wearable electronic device provides a new method for the development of photothermal responsive conductive hydrogels.
Light‐responsive reversible two‐way shape memory polymers (2W‐SMPs) are highly promising for many fields due to indirect heating, clean, and remote control. In this work, a composite with both thermal‐ and near‐infrared (NIR) light‐induced reversible two‐way shape memory effect (2W‐SME) is prepared by doping extremely little quantities of 2D non‐layered molybdenum dioxide nanosheets (2D‐MoO2) into semicrystalline poly(ethylene‐co‐vinyl acetate) (EVA) networks. This is the first report on light‐induced reversible two‐way shape memory composites employing 2D‐MoO2 as photothermal fillers. Upon switching the NIR light on and off, due to the excellent photothermal feature and stability of 2D‐MoO2, the composite exhibits remarkable light‐induced reversible 2W‐SME. A light‐driven actuator for sensing applications is designed based on the composite and the circuit, where the lamp acting as an alarm can raise and fade upon responding to NIR light. A completely flexible, fuel‐free self‐walking soft robot is designed based on the advantages of the light‐responsive reversible 2W‐SMPs. Additionally, the composite acting as a light‐fueled crane is able to lift and lower a load that is 3846 times its own weight. The results demonstrate that the prepared composite has a promising prospect for applications as actuators, self‐walking soft robot and crane.
Stimulus-responsive
intelligent hydrogel actuators have highly
promising applications in the fields of soft robotics, smart manipulators,
and flexible devices. Near-infrared (NIR) light is considered an ideal
method to trigger the response behavior remotely and precisely. In
order to realize the excellent optical transmittance and photothermal
property of NIR-responsive hydrogels at the same time, two-dimensional
nonlayered MoO2 nanosheets (2D-MoO2) with excellent
photothermal efficiency (62% under an NIR light irradiation of 808
nm), splendid chemistry stability, and low preparation cost are used
as photothermal agents and incorporated into the poly(N-isopropylacrylamide) (PNIPAM) hydrogel network, forming the 2D-MoO2/Laponite/PNIPAM ternary nanocomposite hydrogel (TN hydrogel).
It is remarkable that compared with the GO and MXene hydrogels with
the same agent content (1.0 mg mL–1) and thickness
(1 mm) whose transmittance values are only ∼5% at 600 nm, the
TN hydrogel shows a similar NIR-responsive temperature, but much higher
optical transmittance (∼53%). Besides, of the three hydrogels
with similar transmittance, the TN hydrogel shows a much higher NIR-responsive
temperature. The TN hydrogel with a low loading of 2D-MoO2 (1.5 mg mL–1) can produce a significant temperature
increase of ∼30 °C after the application of 0.8 W cm–2 NIR light irradiation for 15 s. Impressively, the
TN hydrogel exhibits excellent anti-fatigue property, keeping a fast
response and temperature rise behavior even after 50 times of heating–cooling
cycles. The flexibly controllable and reversible deformation is realized
by a well-designed bilayer structure even in harsh environments. The
transparent and asymmetric bilayer hydrogel is further used as a soft
manipulator to capture objects visually and accurately. The NIR light-controlled
microvalve based on this composite hydrogel is also demonstrated.
This work provides a novel kind of transparent hybrid NIR response
hydrogel for the further development of smart, programmable, reversible
hydrogel-based actuators and soft robotics.
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