Studies on Multipurpose Liquid Repelling Functional Coatings for Various Industrial Applications

Abstract

Glass and metals have many applications in different fields like automobiles, solar panels, and also in the preparation of different industrial equipment. However, these surfaces are prone to many problems such as accumulation of dirt, corrosion, and fogging, due to their water and oil-loving nature. Different treatment methods have been implemented for the removal of oil and water from these surfaces. But these treatment methods have many disadvantages such as high operating costs, reduction in efficiency, and causing of different secondary pollutions which make the work more complicated. To overcome these problems, coatings on the surfaces were planned to be developed which can prevent the accumulation of water and dirt. Besides the above problems, the concern of pollution caused by oil spills on the water surface is also addressed. The oil- polluted water bodies harm marine animals, human life, and yield of the industries as it can reduce the efficiency of the machinery. Different treatment methods are used which have drawbacks of low separation efficiency, poor recyclability, and long processing time. Oil and water pose different wettability behavior for a particular surface. This property of different wettability helps in the separation of oil from water. Therefore in view of aforesaid problems, attempt has been made to develop superhydrophobic and superliquiphobic/superamphiphobic surfaces. In the present work, the superhydrophobic coating has been developed on a glass surface by using SiO2 microparticles modified by octadecyltrichlorosilane using the dip-coating technique. Hydrophilic property of glass surface was changed to superhydrophobic with water contact angle (WCA) of 165°±6° and sliding angle 2° ± 0.5° after a single dip-coating cycle. Superhydrophobic steel mesh was developed by chemically etching the surface in a solution of FeCl3 + HCl and then immersing the etched mesh in hexadecyltrimethoxysilane. Change in WCA was observed after etching as it reduces to 21° ± 4° and after coating with HDTMS WCA increased to 167° ± 3° and sliding angle of 6° ± 1°. Superliquiphobic/ superamphiphobic coatings were prepared on aluminum and steel surfaces by employing dip coating and drop-casting methods respectively using sol-gel of 1H, 1H, 2H, 2H, perfluorooctyltrichlorosilane modified SiO2 nanoparticles. The prepared superliquiphobic/ superamphiphobic surface was observed to repel liquids with surface energy as low as 27 mN/m (oil). Oil contact angles (OCA) were achieved as 155° ± 4° and sliding angle of 6°±0.5° and 157° ± 2° and sliding angle of 6°±1° for aluminum and steel surfaces respectively. The properties of the prepared coatings on different surfaces were examined by the contact angle, surface morphology, and FTIR analysis. Further, the effect of impact velocity of droplets on the coating surface was also investigated. It was observed that with an increase in water impact velocities, the transition from Cassie-Baxter to Wenzel takes place as the pinning of the droplet was seen on the superhydrophobic coated surface and bouncing was observed for all impact velocities for superliquiphobic surface. Similarly, different behaviors were observed for different liquids on superliquiphobic surfaces. Sticking at different impact velocities were observed for glycerol and hexadecane because of high viscosity and low surface energy, respectively. To make these coatings industrially applicable, experiments were carried out to verify the stability and durability of the coated samples. The samples were exposed to high temperatures, different pH solutions, and different mechanical disturbances such as abrasion, adhesion, twisting, bending, and jet impact tests which confirmed the stability and durability of the coatings. Also, mathematical correlations were developed for wettability and surface etching using different system parameters based on dimensional and statistical analysis. Experimental results were compared with the calculated data where the standard deviations were found to be below 10 for all cases thereby confirming the experimental results. The aforesaid prepared samples are thus recommended to be used for different applications such as self-cleaning, anti-fogging, and oil-water separation.