Carbon‐Based Photothermal Actuators

Abstract

Actuators that can convert environmental stimuli into mechanical work are widely used in intelligent systems, robots, and micromechanics. To produce robust and sensitive actuators of different scales, efforts are devoted to developing effective actuating schemes and functional materials for actuator design. Carbon-based nanomaterials have emerged as preferred candidates for different actuating systems because of their low cost, ease of processing, mechanical strength, and excellent physical/chemical properties. Especially, due to their excellent photothermal activity, which includes both optical absorption and thermal conductivities, carbon-based materials have shown great potential for use in photothermal actuators. Herein, the recent advances in photothermal actuators based on various carbon allotropes, including graphite, carbon nanotubes, amorphous carbon, graphene and its derivatives, are reviewed. Different photothermal actuating schemes, including photothermal effect-induced expansion, desorption, phase change, surface tension gradient creation, and actuation under magnetic levitation, are summarized, and the light-to-heat and heat-towork conversion mechanisms are discussed. Carbon-based photothermal actuators that feature high light-to-work conversion efficiency, mechanical robustness, and noncontact manipulation hold great promise for future autonomous systems. and most have high photothermal conversion efficiencies. [55][56][57][58] With excellent thermal conduction characteristics, carbon materials can transfer the as-obtained thermal energy to the heat-sensitive materials, achieving effective photothermal actuation. [59,60] In addition, carbon materials have many advantages, such as excellent physical and chemical stability, high mechanical strength, conductivity, as well as tunable light absorption properties, which allow for broad application of carbon-based actuators. [61] In this review, we focus on the recent advancements in carbon-based photothermal actuators and highlight their unique advantages, good performance, and potential for future applications. Specific light-to-heat conversion mechanisms and strategies that enable photothermal actuation are discussed. The performance of various photothermal actuators focusing on energy conversion, response/recover time, stability, mechanical strength, and actuating manners has been reviewed in details. Figure 1 shows a summary of typical actuators constructed of different carbon-based materials and their possible light-to-work mechanisms, including photothermal expansion, desorption, phase change, Marangoni effect, and magnetic susceptibility change. In addition, the advantages and limitations of carbon-based photothermal actuators and the current challenges in this field are discussed in Section 4. The development of carbon-based photothermal actuators may stimulate rapid progress in various smart devices for cutting-edge applications.

An Autonomous Soft Actuator with Light‐Driven Self‐Sustained Wavelike Oscillation for Phototactic Self‐Locomotion and Power Generation

“…Besides LCN‐based photoactuators, there exists another type of attractive photoactuator, mainly composed of nanocarbon (e.g., carbon nanotube (CNT) or graphene (RGO)) and polymer composite, which generates deformation owing to the photothermal conversion of nanocarbon and thermal expansion of polymer composite. These nanocarbon‐based photothermal actuators possess advantages of easy fabrication, multiform deformation, and operation through a convenient light source including white light or even sunlight, which show promise in the development of self‐oscillating autonomous actuators and related devices 43–51. For example, Yu et al report visible‐light‐driven graphene oxide/polymer nanocomposites exhibiting a unique tumbler type of movement 51.…”

Controlling Long‐Distance Photoactuation with Protein Additives

“…Graphene‐based photothermal bilayer actuators typically consist of two layers with different CTEs and can generate bending under light stimulation due to the asymmetric volume change. [ 12 ] The interface between the two layers plays a role not only in heat conduction but also in force transmission; thus, strong interfacial adhesion is needed to avoid delamination, improve force transfer, and finally result in better actuation performance.…”

“…Making full use of the easy synthesis and solution‐processing capability of graphene oxide (GO), the reduced graphene oxide (rGO) has been widely used to develop graphene‐based nanocomposites. [ 12 ] The rGO holds great promise in the construction of long‐distance photothermal bilayer actuator. It is known that three main distinct characteristics, the rGO dispersion state within the matrix, [ 13 ] the integrity of the aromatic network of rGO, [ 14 ] and the adhesion strength between two layers, [ 15 ] affect the performance of rGO‐based photothermal bilayer actuators.…”

Harnessing Solar‐Driven Photothermal Effect toward the Water–Energy Nexus

“…Due to strong absorption property (up to 98% in visible and near-infrared region) [60] and high thermal conductivity (6000 W m −1 k −1 ), [72] these CNT-based photothermal convertors can not only efficiently generate a lot of thermal energy, but also fast transfer thermal energy into surrounding medium via radiation and conduction method. These increased conjugated π bonds will result in a red-shift of the absorption light spectrum, which greatly benefits in the solar energy utilization efficiency.…”