# Micro-Actuators with Light and Magnetism Dual-Control for Maneuverable Movements
## 3 Results and Discussion  
### Preparation and Properties of C/Fe\({}_{3}\)O\({}_{4}\)/PDMS Films  
Figure 1a shows the preparation process of C/Fe\({}_{3}\)O\({}_{4}\)/PDMS films. Carbon and Fe\({}_{3}\)O\({}_{4}\) powders are employed as additives and mixed with PDMS, which was mixed with a curing agent (10:1 by weight). The well-mixed composite was dropped on slide substrate and cured at 80 \({}^{\circ}\)C for 30 min. Figure 1b presents the XRD images of carbon and Fe\({}_{3}\)O\({}_{4}\), confirming the amorphous nature of the C powder and the high purity of Fe\({}_{3}\)O\({}_{4}\). The scanning electron microscopy (SEM) image of the samples illustrates obvious irregular folds in Figure 1c, which are attributed to the interaction between PDMS and Fe\({}_{3}\)O\({}_{4}\). During heating, the internal energy of the Fe\({}_{3}\)O\({}_{4}\)/PDMS system increased and facilitated the formation of non-joint-chain dimethylsiloxane structures, thereby enhancing the adhesion properties of the materials [34]. As for the optical actuator, carbon black and Fe\({}_{3}\)O\({}_{4}\) played crucial roles in thermal conversion. Figure 1d illustrates the superior tensile properties of the composite film. A uniform film, originally 73.4 mm in length, was readily stretched to 105 mm at a tensile rate of 1.43. In contrast, a PDMS film of the same length without any additives was stretched to only 88 mm, demonstrating less stretchability. These novel properties indicate the potential of this flexible, soft, and easily stretchable film to serve as a new type of robot skin in the domain of liquid surface-driven robotics. Notably, the cured films exhibit superior elasticity and are softer compared to pure PDMS films. Furthermore, the composite thin film holds significant potential in the realm of motion technology for optical driving transport actuators and small soft robots operating on liquid surfaces.  
Figure 1: Preparation process and properties of C/Fe\({}_{3}\)O\({}_{4}\)/PDMS film. (**a**) Preparation process of C/Fe\({}_{3}\)O\({}_{4}\) /PDMS films. (**b**) XRD patterns of carbon and Fe\({}_{3}\)O\({}_{4}\). (**c**) SEM image of film. (**d**) Optical photographs of tensile comparison between C/Fe\({}_{3}\)O\({}_{4}\)/PDMS film and pure PDMS film.  
To further investigate the impact of Fe\({}_{3}\)O\({}_{4}\) content on composite films, several samples with varying proportions were prepared (Table 1). All prepared film samples possessed identical specifications, with the carbon powder content fixed at a mass ratio of 1:20 to PDMS. The distinction lay in the mass ratios of PDMS to Fe\({}_{3}\)O\({}_{4}\) powder, which were 10:1, 10:2, and 10:3, respectively, for samples designated as 1, 2, and 3 herein. However, when the ratio reaches 10:4, curing of the PDMS becomes challenging. The hydrophobic properties of the samples were also evaluated. The water contact angles of all samples exceeded 90 degrees, facilitating enhanced movement of the drives on the water surface. The instantaneous temperatures of the samples under laser irradiation (100 mW, 532 nm) were measured, and the temperature differences were derived by subtracting the ambient temperature. As anticipated, the Fe\({}_{3}\)O\({}_{4}\) content was positively correlated with the temperature difference.