Optimization of Superhydrophobic Surface Production Using Ambient-Pressure Dried Silica-Based Aerogels

Superhydrophobic surfaces exhibit particular properties that make them functional in various anti-sticking, anti-contamination, self-cleaning and drag reduction applications. Though such surfaces are found in nature - most notably the lotus leaf - they are difficult to produce. There are numerous methods and techniques for fabricating superhydrophobic surfaces. One such method is the sol-gel method, in which aerogel, a highly porous and lightweight material that can be made hydrophobic or superhydrophobic, is coated onto a surface. The purpose of this project is to devise a simple and repeatable procedure for making hydrophobic silica aerogel coatings that can be used for drag reduction. Hydrophobic coatings were made using a methlytrimethoxysilane based recipe with varying amounts of methanol and water. Oxalic acid was added for hydrolysis of the precursor solution and  ammonium hydroxide was used as a catalyst to form a wet-gel. The wet-gel was dissolved using methanol and the resulting homogeneous solution was  applied to the surface of a microscope slide and dried at various temperatures. A Plackett-Burman experimental screening process was conducted to determine which factors in the aerogel production and coating process had the greatest effect on the quality and hydrophobicity of the coating. The application method, layers of coating, drying temperature and drying time were found to have the greatest effect on the hydrophobicity. A subsequent Randomized-Block experimental design was used to optimize the coating method and chemical recipe. Slides were coated and characterized using sessile-drop contact angle measurements, scanning electron microscopy (SEM) and surface area and porosity measurements. The highest contact angle reached was 154^o. SEM imaging shows nanometer-scale sized spherical shaped aerogel formation and an evenly coated surface.