Preparation of Super-hydrophobic Silicone Rubber Coating by Powder Spraying Method

Most current methods for constructing superhydrophobic surfaces on rubber substrates are too complex to carry out; therefore, it is essential to investigate a simple method. High-temperature vulcanized silicone rubber (HTV) and polydimethylsiloxane (PDMS), which have the advantage of low surface energy, combined with the hydrophobic properties of silicon dioxide (SiO2), were selected to prepare superhydrophobic coatings on silicone rubber surfaces in this paper. The specific steps are as follows. The rubber matrix was prepared first. The HTV rubber and vulcanizing agent were added in an open refiner until the vulcanizing agent was uniformly mixed in the HTV rubber. The rubber was then vulcanized using a fully automatic plate vulcanizer, where the vulcanization temperature was 175 °C and the time was 10 min. The vulcanized rubber was cooled at room temperature for 24 h, and then polished with a metallographic polishing machine. The rubber was polished in one direction using the same sandpaper and the machine was never moved. After polishing, the rubber was placed in a beaker with alcohol and cleaned using an ultrasonic cleaner. Since the rubber matrix had been accomplished, a mixture of 3 g PDMS and 0.3 g curing agent was added into the beaker containing the rubber matrix for PDMS coating. After curing at room temperature for 20 min, the silica powder was evenly spread on the surface of the PDMS using a sieve. Then the beaker was placed in a drying oven and cured at 80 °C for 2 h. After curing, the prepared superhydrophobic silicone rubber was removed from the oven, and excess silica powder was removed using nitrogen gas to prevent excess silica powder from affecting the hydrophobicity of the prepared coating. The hydrophobicity of the prepared superhydrophobic surfaces was assessed. First, the contact angles of the original silicone rubber samples and the HTV / PDMS-SiO2 superhydrophobic silicone rubber were tested using a contact angle measuring instrument. Next, the surface microstructures of the HTV / PDMS-SiO2 superhydrophobic silicone rubber samples and the PDMS-SiO2 superhydrophobic coating were analyzed by observing their cross-sections using scanning electron microscopy and 3D morphology. Finally, the HTV / PDMS-SiO2 superhydrophobic silicone rubber was subjected to water drop bounce and self-cleaning tests to verify its superhydrophobic performance. The results showed that the average static contact angle of the HTV / PDMS-SiO2 superhydrophobic surface reached 154.5°, which was 37.5% higher than the average static contact angle of 112.4° for pure silicone rubber. The prepared HTV / PDMS-SiO2 superhydrophobic surface had a rough structure with many micro-nano bumps and a surface roughness Sa of 35.695 µm. The droplet spreading diameter and first bounce height when the droplet touched the superhydrophobic surface increased with increasing droplet height when the droplet volume was constant. When the droplet height was constant, the droplet spreading diameter and the initial bounce height were proportional to the droplet volume. In this study, an HTV / PDMS-SiO2 superhydrophobic coating was constructed using a powder coating method, which has the disadvantages of low strength and poor wear resistance. Thus, the constructed coating is not suitable for high-strength engineering, and its superhydrophobic performance cannot be guaranteed during long-term use. It has been found that superhydrophobic coatings can be constructed by constructing micro-nano-protrusions on a surface with low surface energy material. The PDMS curing process combined with the powdering process to construct superhydrophobic micro-nano structures provides a simple and low-cost solution for the study of superhydrophobic surfaces on silicone rubber. If the durability of the coating can be improved, it will be of great significance for the wider application of superhydrophobic silicone rubber surfaces. © 2023 Chinese Mechanical Engineering Society. All rights reserved.