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2 Physicochemical Problems of Mineral Processing

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Fabrication of transparent polysiloxane coatings on a glass support via the sol-gel dip coating technique and the effect of their hydrophobization with hexamethyldisilazane

Chodkowski Michał, Terpiłowski Konrad, Pasieczna-Patkowska Sylwia

Physicochemical Problems of Mineral Processing

2020

Vol. 56, iss. 6

76--88

This study aimed at synthesis, preparation, and physicochemical properties investigation of undoped polysiloxane-based coatings deposited on the glass supports. The other goal was to test the effectiveness of their hydrophobization with hexamethyldisilazane at an elevated temperature using a bubbler. The coatings were obtained in a sol-gel process by acid-assisted hydrolysis of tetraethoxysilane and they were applied to the glass supports using the dip coating technique with various withdrawal speeds. The synthesized composition was scanned using TurbiscanLAB and its particle size was determined by means of the dynamic light scattering technique. The obtained surfaces were examined based on the water wettability measurements, photoacoustic spectroscopy, and transmittance measurements. It was found that the stability of the sol did not change during the dip-coating. Smooth, homogeneous, uniform, hydrophobic, and transparent coatings on the glass supports were obtained. Their wettability was determined by the contact angle in the range from 83.5 to 95.2 degrees and very low contact angle hysteresis. The hydrophobic effect obtained by modification with hexamethyldisilazane appears to be permanent – the contact angles do not change significantly after 7 days. The synthesized sol composition appears to be a good starting point for its chemical and physical modification for hydrophobicity increase and surface properties modification. Moreover, the hydrophobization of the coatings with hexamethyldisilazane at an elevated temperature using the bubbler did not have the desired effect.

Surface properties of the doped silica hydrophobic coatings deposited on plasma activated glass supports

Chodkowski Michał, Terpiłowski Konrad, Goncharuk Olena

Physicochemical Problems of Mineral Processing

2019

Vol. 55, iss. 6

1450--1459

The paper discusses preparation and characteristics of silica hydrophobic layers deposited on the plasma-modified glass supports. The surfaces were investigated using wettability measurements, profilometry, photoacoustic and infrared spectroscopy, X-ray photoelectron spectroscopy as well as scanning electron microscopy. The wettability measurements showed that the obtained surfaces are hydrophobic – the water contact angle was in the range of 140-150 degrees. The photoacoustic and infrared spectroscopy as well as X-ray photoelectron spectroscopy disclosed the surface compositions, particularly that of the hydrophobic alkyl groups deposited on them. They were methyl groups introduced during hydrophobization by hexamethyldisilazane. In addition, it was found that the number of groups on the surface depends on the kind of plasma by which the supports were activated. The optical profilometer showed differences in the surface roughness which affects their hydrophobicity. Moreover, the surface free energies were determined using the contact angle hysteresis method. They disclosed differences in each surface, depending on the way of supports activation. The largest hydrophobicity was obtained on the layer deposited on the support activated by the argon plasma. However, support activation by the air plasma resulted in a decrease of hydrophobicity compared to that of the non-activated surface.