A microgripper is an essential part of the micromanipulation system. As the end effector of the microoperating system, the jaw end face of the microgripper is prone to wear, adsorption of impurities, ice, or frost during operation. Most traditional microgrippers are integrally machined, and the overall replacement will result in wasted resources. This study reports a detachable microgripper with superhydrophobic properties. First, a rough microstructure was machined on the end face of the jaws where the operation is performed using a nanosecond laser with a central wavelength of 1064 nm. Then, they are modified by immersing them in a nontoxic stearic acid solution. Thus, a bionic superhydrophobic surface is obtained. This surface has excellent corrosion resistance, self-cleaning, antiicing, and antibacterial properties. X-ray photoelectron spectroscopy (XPS) technique is employed to analyze the chemical composition of the pristine aluminum (Al-Ⅰ) and superhydrophobic aluminum (Al-Ⅱ) surfaces; the corrosion resistance of both surfaces in acid, salt, and alkali environments is tested using electrochemical experiments. Further, the antifouling, antifreezing, and antibacterial properties of both surfaces are tested using self-cleaning, antiicing, and antibacterial experiments. We expect that our basic strategies and findings will enhance the performance and extend the service life of the microgrippers.
Because the microgripper is made of 7075 space aluminum used to facilitate later observation, testing, and analysis, a 7075 aluminum sample with size and thickness of 10 mm×10 mm and 1 mm, respectively, is used for the test instead of the end face of the jaws. First, a nanosecond laser is used to etch a grid-like microstructure on the surface of the sample, and then it is immersed in a nontoxic stearic acid solution with a concentration of 0.05 mol/L for 30 min to reduce the surface free energy. Further, it is removed and placed in a drying oven at 60 ℃ for 1 h. The sample surface will acquire the expected superhydrophobic properties using this procedure. According to the functional requirements of the microgripper, the prepared superhydrophobic sample surfaces are analyzed for surface composition and tested for corrosion resistance, self-cleaning, antiicing, and antibacterial properties. The chemical composition of Al-Ⅰ and Al-Ⅱ surfaces is detected using the XPS technique. Further, the morphology of the sample surfaces before and after corrosion by acid, salt, and alkali is characterized using scanning electron microscopy. The antiicing and self-cleaning performance of the sample surfaces are evaluated using an environmental test chamber and self-designed self-cleaning experiments. The bacterial distribution and survival status of the sample surfaces are characterized using laser confocal microscopy, and the antibacterial performance is characterized using plate coating experiments to calculate the bacterial inhibition rate.
The lattice-like microstructures obtained from the sample surface preparation have high superhydrophobicity with average contact and rolling angles of 156.7° and 1.088°, respectively. The XPS test results show that the surface of both samples mainly contains C, O, and Al elements. After laser irradiation, the generated Al2O3 on the surface caused the O atomic number fraction to increase by 24.51%. The C 1s high-resolution spectra of the superhydrophobic samples exhibit a significant increase in C atomic number fraction following the stearic acid modification treatment, indicating that stearic acid reacted with the surface Al to form low surface energy aluminum stearate during the chemical modification process. The C—C (H) content is as high as 82.81%, occupying the strongest peak, which indicates that the long-chain molecules of stearic acid have successfully adhered to the surface of the Al-Ⅱ sample in the form of aluminum stearate (Fig. 5). Electrochemical experiments and SEM results show that the corrosion resistance of the superhydrophobic surface in a salt solution is better than its resistance to acids and bases; the total impedance modulus of superhydrophobic Al-Ⅱ sample is better than that of pristine Al-Ⅰ sample. This implies that the superhydrophobic surface with a rough microstructure can significantly enhance the corrosion inhibition of aluminum materials (Figs. 68, Table 1). The self-cleaning test results show that the droplets can effectively remove the impurities from the surface of the Al-Ⅱ sample, indicating that the superhydrophobic surface has a good self-cleaning ability (Fig. 10). The results of the twenty-minute antiicing experiments show that the Al-Ⅱ sample has excellent superhydrophobicity with low adhesion ability and no significant icing occurred during the test, whereas the adhering ice layer on the surface of the Al-Ⅰ sample has a mass of 1.283 g and shows poor antiicing performance in the cryogenic environment (Fig. 11). The results of laser confocal microscope characterization in the antibacterial experiment show that the number of strains adhering to the surface of the Al-Ⅱ sample is significantly lower than that of the Al-Ⅰ sample, indicating that the prepared superhydrophobic sample has a strong resistance to bacterial adhesion (Fig. 12). Further, the results of the plate-coating experiment show that the antibacterial rate of the Al-Ⅱ sample is 3.8 times higher than that of the original Al-Ⅰ sample, which proves that the aluminum-based superhydrophobic surface with lattice-like microstructure has certain bactericidal properties (Table 2).
In this study, we design and construct a detachable microgripper with a bionic superhydrophobic structure in the jaw end of the gripper body, which addresses several problems of the traditional microgripper. The main research contents and innovations are as follows: 1)the microgripper’s base body and the left and right clamping bodies are designed separately and connected by bolts. This design increases the flexibility of the microgripper, which can replace the corresponding body based on different clamping objects and working conditions. When the jaw end face is damaged by repeated use, it is unnecessary to replace the whole microgripper; however, only the body part can be replaced. 2)The laser-textured jaw end faces are soaked in a low surface energy stearic acid solution to obtain superhydrophobic properties. The surface obtained through this method has a rough microstructure and low surface energy, thus forming an air layer between the material and the liquid; it effectively prevents the contact of the material surface with corrosive solutions, common water droplets, and bacterial solutions inhibiting the adhesion of droplets. This enables the jaw end faces to acquire self-cleaning, anticorrosion, antiicing, and antifrost properties, thus effectively enhancing the clamping performance of the microgripper.
