# Micro-Actuators with Light and Magnetism Dual-Control for Maneuverable Movements
## 1 Introduction  
A micro-actuator based on the Marangoni effect presents significant potential for pioneering applications in the realm of self-driven and liquid surface robot development. In recent years, extensive research has demonstrated the unique advantages of the Marangoni effect in converting light, heat, and chemical energy into mechanical energy [1, 2, 3, 4, 5, 6]. Owing to its substantial potential for practical applications in liquid surface transport, more and more researcher have focused on the Marangoni effect within the realms of self-assembly and self-propulsion [7, 8, 9, 10, 11, 12]. This energy conversion is caused by inhomogeneous surface tension at the two-phase liquid interface, which is highly sensitive to variations in temperature and chemical composition. According to the Marangoni phenomenon, Marangoni actuators [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] are an effective method for material transport. In the field of interfacial self-assembly, the Marangoni effect emerges as a potent strategy for mitigating the coffee ring effect [20, 21, 22, 23, 24], which is related to chemical properties. The chemical driven Marangoni effect exhibits exceptional potential for driving substancesacross fluid surfaces [25]. For example, [PERSON] et al. developed a micro-boat propelled by isopropyl alcohol, investigating the feasibility of utilizing such micro-boats for the potential transport of target substances within microfluidic systems [26]. [PERSON] et al. reported an experiment involving an agarose gel sheet embedded with camphoric acid, which spontaneously initiated movement in response to a surface tension gradient on the water surface [27]. However, a chemical-driven Marangoni effect presents some challenges, including environmental unfriendliness and long-distance movement. Photoresponse Marangoni actuators offer unique advantages to solve these problems [28]. Among previous micro-actuators, photothermal conversion materials played an important role in energy-autonomous microfluidic systems and drug delivery. In particular, carbon, as a high-performance photothermal conversion material, has garnered widespread attention from researchers for Marangoni actuators. For example, [PERSON] et al. pioneered laser-induced graphene (LIG) strips with asymmetric adhesive-photothermal bifunctionality for Marangoni propulsion control [29]. In addition, [PERSON] et al. demonstrated a fuel-storage-integrated microvessel utilizing passive capillary triggering for on-demand ethanol release in Marangoni propulsion [30]. Furthermore, [PERSON]'s team achieved 62% photomechanical conversion efficiency in microgear arrays through optimized thermal capillary actuation at fluid interfaces and established a single-step laser ablation technique for fabricating Janus-structured floating devices with synergistic light absorption (>90% at 808 nm) and hydrodynamic drag reduction capabilities (42% reduction compared to smooth surfaces) [31]. Optical actuators exhibit efficient light-to-power conversion, and their capability for flexible and controllable transportation offers a novel direction for the development of new surface robot types. In addition, [PERSON] et al. designed and prepared a dual-mode-driven Marangoni hydrogel actuator, which exhibits excellent ethanol loading capacity but also demonstrates both sustained motions [32]. [PERSON] et al. developed anisotropic hydrogel actuators with multimodal stimuli-responsiveness, which consisted of clay nanosheets, Graphene Oxide (GO) nanosheets, and Fe\({}_{3}\)O\({}_{4}\) nanoparticles [33]. However, due to low penetration of light, the movement of optical actuators is still restricted inside the liquid to a certain extent. In this study, we demonstrate the preparation of hydrophobic materials with efficient photothermal effects for optical actuators, achieved through the direct incorporation of carbon black and Fe\({}_{3}\)O\({}_{4}\) into PDMS.