Effects of particle size and modifier amount on hydrophobicity of as-synthesized and modified nano-silica spheres

Abstract

Superhydrophobic coatings possess dust-proof and self-cleaning characteristics. Reducing surface energy and improving nanoscale roughness is considered to be crucial for the development and design of superhydrophobic coatings as they can result in significant reduction in the adhesion between solid surfaces and water droplets. In this work, silica spheres were synthesized and hydrophobically modified using the Stober process. Surface morphology and particle size as well as grafting modification effect, grafting quality, hydrophobic properties, and chemical hydrophobic modification mechanism of synthesized silica spheres were analyzed. Results show that the size of synthesized particles is significantly correlated with the concentration of ammonia catalyst, and their hydrophobic properties are significantly correlated with the amount of dichlorodimethylsilane (DCDMS) modifier. Superhydrophobic behavior is obtained for modified silica sphere (MSS) samples with particle sizes of 850, 400, 320, and 120 nm by varying the molar ratio (MR) of DCDMS to silica spheres (MR = 4, 8, and 16). The optimal amount of modifier is closely related to the size of spheres with fixed mass of silica spheres. In addition, large MSS arrays can provide rougher surfaces and thus trap more air within the voids, which resulting in stable hydrophobic properties. This work can provide guidance for the design of superhydrophobic coatings.