TEOS based water repellent silica films obtained by a co-precursor sol–gel method

• Published in: Smart Materials and Structures Vol. 18; no. 9; pp. 095017 - 095017 (6)
• Main Authors: Latthe, Sanjay S, Hirashima, H, Rao, A Venkateswara
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.09.2009; Institute of Physics
• Subjects: Adsorption and desorption kinetics; evaporation and condensation; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Water; Scanning electron microscopy; Infrared spectroscopy; Fourier transformation; Hydrophobic compound; Contact angle; Hydrophobicity; Experimental study; Silica; Heat treatments; Thermal stability; Angular measurement; Optical measurement; Modelling; Hydrophilic compound; Sol-gel process; Methanol
• ISSN: 0964-1726; 1361-665X
• DOI: 10.1088/0964-1726/18/9/095017

The nature of interfaces between water and hydrophobic materials has been a subject of great interest. Experimental results from tetraethoxysilane (TEOS) based hydrophobic silica films synthesized by the two step sol-gel process using hexadecyltrimethoxysilane (HDTMS) as a co-precursor are described. The molar ratio of TEOS, methanol (MeOH), acidic water (0.001 M, oxalic acid), and basic water (8 M, NH4OH) was kept constant at 1:66.66:6.76:6.66, and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 22.9 X 10-2. The maximum contact angle of 125 deg was obtained for M = 22.9 X 10-2. It is observed that the water contact angle value on the HDTMS modified films remained stable at 125 deg, after heat treatment up to 235 deg C. However, the water contact angle value decreased to 52 deg in the case of unmodified films, indicating the improvement in the thermal stability using HDTMS as a co-precursor. The hydrophobic silica films retained their hydrophobicity up to a temperature of 235 deg C and above this temperature the films became hydrophilic. The hydrophobic silica films were characterized by surface roughness studies, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, contact angle measurements, and % optical transmission.