Sanjay S. Latthe

Preparation of MTMS based transparent superhydrophobic silica films by sol-gel method.

Superhydrophobic surfaces with water contact angle higher than 150 degrees generated a lot of interest both in academia and in industry because of the self-cleaning properties. Optically transparent superhydrophobic silica films were synthesized at room temperature (27 degrees C) using sol-gel process by a simple dip coating technique. The molar ratio of MTMS:MeOH:H(2)O (5 M NH(4)OH) was kept constant at 1:10.56:4.16, respectively. Emphasis is given to the effect of the surface modifying agents on the hydrophobic behavior of the films. Methyl groups were introduced in the silica film by post-synthesis grafting from two solutions using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents in hexane solvent, individually. The percentage of silylating agents and silylation period was varied from 2.5 to 7.5% and 1 to 3 h, respectively. The TMCS modified films exhibited a very high water contact angle (166+/-2 degrees) in comparison to the HMDZ (138+/-2 degrees) modified films, indicating the water repellent behavior of the surface. When the TMCS and HMDZ modified films were heated at temperatures higher than 350 degrees C and 335 degrees C, respectively, the films became superhydrophilic; the contact angle for water on the films was smaller than 5 degrees. Further, the humidity study was carried out at a relative humidity of 85% at 30 degrees C temperature over 30 days. The films have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), % optical transmission, humidity tests and contact angle (CA) measurements.

Water repellent porous silica films by sol-gel dip coating method

The wetting of solid surfaces by water droplets is ubiquitous in our daily lives as well as in industrial processes. In the present research work, water repellent porous silica films are prepared on glass substrate at room temperature by sol-gel process. The coating sol was prepared by keeping the molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), water (H(2)O) constant at 1:12.90:4.74, respectively, with 2M NH(4)OH throughout the experiments and the molar ratio (M) of MTES/Ph-TMS was varied from 0 to 0.22. A simple dip coating technique is adopted to coat silica films on the glass substrates. The static water contact angle as high as 164° and water sliding angle as low as 4° was obtained for silica film prepared from M=0.22. The surface morphological studies of the prepared silica film showed the porous structure with pore sizes typically ranging from 200nm to 1.3μm. The superhydrophobic silica films prepared from M=0.22 retained their superhydrophobicity up to a temperature of 285°C and above this temperature the films became superhydrophilic. The porous and water repellent silica films are prepared by proper alteration of the Ph-TMS in the coating solution. The prepared silica films were characterized by surface profilometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity tests, chemical aging tests, static and dynamic water contact angle measurements.

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

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 ? 10?2. The maximum contact angle of 125? was obtained for M = 22.9 ? 10?2. It is observed that the water contact angle value on the HDTMS modified films remained stable at 125?, after heat treatment up to 235??C. However, the water contact angle value decreased to 52? 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??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.