Self-Locomotive Soft Actuator Based on Asymmetric Microstructural Ti₃C₂T_x MXene Film Driven by Natural Sunlight Fluctuation

Abstract

Soft actuators and microrobots that can move spontaneously and continuously without artificial energy supply and intervention have great potential in industrial, environmental, and military applications, but still remain a challenge. Here, a bioinspired MXene-based bimorph actuator with an asymmetric layered microstructure is reported, which can harness natural sunlight to achieve directional self-locomotion. We fabricate a freestanding MXene film with an increased and asymmetric layered microstructure through the graft of coupling agents into the MXene nanosheets. Owing to the excellent photothermal effect of MXene nanosheets, increased interlayer spacing favoring intercalation/deintercalation of water molecules and its caused reversible volume change, and the asymmetric microstructure, this film exhibits light-driven deformation with a macroscopic and fast response. Based on it, a soft bimorph actuator with ultrahigh response to solar energy is fabricated, showing natural sunlight-driven actuation with ultralarge amplitude and fast response (346°in 1 s). By utilizing continuous bending deformation of the bimorph actuator in response to the change of natural sunlight intensity and biomimetic design of an inchworm to rectify the repeated bending deformation, an inchwormlike soft robot is constructed, achieving directional self-locomotion without any artificial energy and control. Moreover, soft arms for lifting objects driven by natural sunlight and wearable smart ornaments that are combined with clothing and produce three-dimensional deformation under natural sunlight are also developed. These results provide a strategy for developing natural sunlight-driven soft actuators and reveal great application prospects of this photoactuator in sunlight-driven soft biomimetic robots, intelligent solar-energy-driven devices in space, and wearable clothing.

Multifunctional Ti3C2Tx MXene/Low-Density Polyethylene Soft Robots with Programmable Configuration for Amphibious Motions

“…So far, the actuators developed possess different structures, such as hydrogels, Janus membranes, , and gradient structure membranes. , Polymers with specific structures and properties, such as shape memory polymers and liquid-crystal polymers, − are commonly used to endow the actuators with designable functions and shape programming. Even commercial general plastics including low-density polyethylene (LDPE) and polypropylene are also used as substrates for thermal expansion. − Among them, the coefficient of thermal expansion (CTE) of LDPE can reach 400 × 10 –6 °C –1 along the orientation direction, much higher than those of most polymers . The remarkable CTE of LDPE makes it highly sensitive to temperature, becoming a prominent substrate of actuators.…”

Tough and Multifunctional Composite Film Actuators Based on Cellulose Nanofibers toward Smart Wearables

“…Considerable research efforts have already been dedicated to the design of various smart actuators that can deform reversibly in response to external stimuli such as humidity, , electricity, , light, , temperature, , and magnetism. , Their successful design and development in current society may be regarded as a green energy-saving intellectualization. Specifically, humidity-responsive actuators have received considerable research attention owing to the environmental friendliness and humidity availability, which hold great potential in many cutting-edge applications such as smart wearables, , soft robots, − artificial muscles, and energy generators. , The two main design strategies for humidity-responsive actuators are to (i) construct bilayer or multilayer structures based on distinct differences in hydrophilicity between different materials or layers and (ii) design single structures composed of one or more hydrophilic materials that respond to inhomogeneous stimuli.…”

Magnetoactive Soft Drivers with Radial-Chain Iron Microparticles

“…Soft robots, having the ability of mimicking the lifelike motions of human or animal body structures or tissues, have attracted a great deal of attention recently. − Driving devices/methods, such as artificial muscles, actuators, micropumps, and some other biomimetic or bioinspired microactuator systems, are one of most important parts in soft robotic systems. − Various functional materials, such as electroactive polymers, , shape memory polymers, , light-active polymers, − or magnetoactive polymers, − can be utilized to drive or construct the soft robot by varying external stimuli. Magnetoactive polymers, being driven by different magnetic fields, may have the widest application potential compared with other functional materials since they can be excited by low voltage [electroactive polymers (>1 kV)] with low requirement of working environments (light-active polymers with the need for optical transparent environments) and large strain (low strain of the shape memory polymers) properties. , At the same time, magnetoactive polymers can provide highest manipulation forces and torques , and can be driven remotely by different magnetic fields in different surrounding media, such as air, liquid, vacuum, or enclosed spaces even, as long as the working surrounding is nonmagnetic insulation .…”