Influence of Glycerol Additive on the Chemical Structure, Hydrophobicity, Morphology and Optical Properties of Sol-gel Based Zirconia Coatings

Abstract

This work represents the influence of glycerol additive on the chemical structure, hydrophobicity, morphology and optical properties of the sol-gel based zirconia coatings. The drying control chemical additives (DCCAs) are found to sustain the porous structure of the materials, which reduces the risk of cracking. Among various DCCAs like oxalic acid, glycerol (GLY), formamide etc., GLY is observed to be an effective DCCA because of its low vapor pressure (2.13 x 10-6 bar at 20oC). Therefore, the effect of GLY additive on the properties of zirconia coatings has been studied by varying the molar ratio of GLY:Zr4+ from 0 to 2.15. During the sol-gel process the molar ratio of ZrPro: PrOH: Acac: H2O was maintained constant as 1:79.8:0.615:35.08, respectively with 0.1 M HCl. The Fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) analyses revealed that the coating material was zirconia. Scanning electron microscope (SEM) images manifested the porous morphology of the zirconia coatings, having the optical transmission larger than 90%. Moreover, the porous nature of the zirconia coatings was confirmed by calculating their refractive indices. The zirconia coatings synthesized using the GLY:Zr4+ molar ratio of 0.429 exhibited the high contact angel of 108o and low refractive index of 1.66, which evidenced their optically transparent and hydrophobic characteristics.