Open Chem., 2019; 17: 798–805 Research Article Alfa Akustia Widati*, Nuryono Nuryono*, Indriana Kartini Design of SiO 2 /TiO 2 that Synergistically Increases The Hydrophobicity of Methyltrimethoxysilane Coated Glass https://doi.org/10.1515/chem-2019-0087 received November 27, 2018; accepted April 8, 2019. Abstract: This research work presents the design of a mixture of SiO 2 /TiO 2 that increases the surface roughness and hydrophobicity of methyltrimethoxysilane (MTMS) coated glass. The deposition of SiO 2 , TiO 2 , and MTMS were conducted using a layer by layer dip coating technique. The SiO 2 /TiO 2 coating was derived from complete hydrolysis of tetraethylorthsilicate and titanium tetraisopropoxide. In order to evaluate and compare the performance of SiO 2 /TiO 2 /MTMS coated glass, the SiO 2 /SiO 2 /MTMS and TiO 2 /TiO 2 /MTMS were also fabricated. SiO 2 /TiO 2 /MTMS samples displayed the highest water contact angle. The topography of surfaces showed that SiO 2 /TiO 2 /MTMS exposed higher surface roughness with micro-nanoscale structures. The sequence of SiO 2 and TiO 2 influenced the water contact angle and the stability of the coatings. SiO 2 / TiO 2 /MTMS produced higher contact angle and stability than TiO 2 /SiO 2 /MTMS. Keywords: SiO 2 /TiO 2 ; MTMS; surface roughness; stable; hydrophobic glass. 1 Introduction The degree of water repellency depends on the surface energy and surface roughness. Several studies reported that surface roughness is a key factor for creating hydrophobic surfaces. Surface roughness can be increased by etching, chemical grafting, and the sol–gel process [1-2]. The sol–gel process is a wet chemical technique, also referred to as chemical solution deposition, which produces particles that are dispersed and aggregated on the surfaces. The clustered particles subsequently afford a highly hierarchical rough surface. Air bubbles are trapped in the grooves between aggregated particles which makes it difficult for water droplets to penetrate the gaps between the surfaces. Hence, surfaces with high roughness tend to follow heterogeneous wetting as the water easily rolls off from the surfaces [3]. The water contact angle depends on the surface roughness, which can be explained by two models: Cassie–Baxter and Wenzel models. Wenzel proposed a model in which water droplets penetrate into surface cavities, while Cassie–Baxter proposed a model in which water in the surface cavities is entrapped in air. Both these models explain the effect of the surface roughness on the water contact angle [2-4]. The correlation between the contact angle and surface roughness based on the Wenzel and Cassie–Baxter models is shown in equations 1 and 2, respectively. (1) (2) where cos θw and cos θCB are the Wenzel and Cassie– Baxter contact angles respectively. r is the roughness factor, which is defined as the ratio of the actual area of the rough surface to the geometric projected area. f1 and f2 are the fractions of the surface occupied by solid/liquid *Corresponding authors: Alfa Akustia Widati, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Sekip Utara, Yogyakarta 55281, Indonesia; Department of Chemistry, Faculty of Science and Technology, Universitas Airlangga, Surabaya 60115, Indonesia, E-mail: alfaakustia@fst.unair.ac.id; Nuryono Nuryono, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Sekip Utara, Yogyakarta 55281, Indonesia, E-mail: nuryono_mipa@ugm.ac.id Indriana Kartini, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Sekip Utara, Yogyakarta 55281, Indonesia Open Access. © 2019 Alfa Akustia Widati, Nuryono Nuryono, Indriana Kartini, published by De Gruyter. This work is licensed under the Creative Commons Attribution alone 4.0 License.