Tribological and Wetting Properties of TiO2 Based Hydrophobic Coatings for Ceramics

Abstract

Hydrophobic and self-cleaning photocatalytic ceramics and concrete with potential for the superhydrophobicity are promising novel materials for civil engineering applications including buildings, bridges, road pavements, and airport runways. Due to embedded liquid-repellent properties, such materials have low water and salt absorption and, therefore, enhanced durability. However, in applications requiring high traction (e.g., tire and pavement), there is a concern that reduced adhesion may compromise the friction. This paper reports on wetting, dry friction, and roughness properties of TiO2 coated (hydrophilic) and polymethyl hydrogen siloxane (PMHS) coated (hydrophobic) self-cleaning ceramic tiles. The coefficient of friction values of the tile–rubber interface do not change significantly with the applications of the coatings up to 0.67 for hydrophilic TiO2 based and up to 0.46 for hydrophobic TiO2 + PMHS coatings versus 0.45 for uncoated reference. Friction has adhesion and roughness-related components and this response can be attributed to the roughness component of friction due to TiO2 coating. The challenges related to hydrophobic coatings, including the durability and future research, are also discussed.

Lotus Effect and Friction: Does Nonsticky Mean Slippery?

“…The effects of micro- and macroscale roughness on surface wetting properties are well established. The characterization and synthesis of superhydrophobic and hydrophilic surfaces have been studied extensively over the years [ 67 , 68 , 69 , 70 , 71 ]. Whether a surface is hydrophobic or hydrophilic depends upon the adhesion of water molecules to the solid surface.…”

“…Lanka et al studied the tribological and wetting properties of TiO 2 -based hydrophobic coatings [ 71 ]. To replicate a system for tire–concrete friction in the laboratory setup, nitrile rubber and ceramic tiles were used.…”

“… ( a ) Contact angle (CA) vs. surface roughness for hydrophobic tiles and ( b ) COF vs. roughness for hydrophilic and hydrophobic samples (reproduced from Reference [ 71 ] with permission). …”

Development of Multifunctional Coatings for Protecting Stones and Lime Mortars of the Architectural Heritage

“…Moreover, a hydrophobic environment could protect the photocatalyst from washing away owing to the rain action (Shajari-Ghasemkheili and Sarraf-Mamoory 2019). In support of this approach, the scientific literature provides some works dealing with photocatalytic-hydrophobic coatings (Kamegawa, Shimizu and Yamashita 2012;La Russa et al 2012;Kapridaki and Maravelaki-Kalaitzaki 2013;Kapridaki et al 2014;Gobakis et al 2015;Kamegawa, Irikawa and Yamashita 2015;Kapridaki and Maravelaki 2016;Aldoasri et al 2017;Colangiuli et al 2019;Lanka et al 2019; Shajari-Ghasemkheili and Sarraf-Mamoory 2019. However, the coatings so far reported for Built Heritage are based on TiO 2 and organic water repellent agents.…”