Hydrophobic Coating Of Glass Surface Using Atmospheric Pressure Dielectric Barrier Discharge Plasma

The wettability of glass was tailored over a wide range by creating a coating layer on its surface using double-dielectric barrier discharge plasma in argon (Ar). Chemical precursors such as tetramethylsilane (TMS) and (3-Aminopropyl)triethoxysilane (APTES) were used to alter the hydrophobicity and mechanical strength of the coating layer. In the plasma-induced deposition process to improve hydrophobicity, the wettability and mechanical strength of the coating layer was varied by the TMS/APTES ratio, treatment time, applied voltage and oxygen content. The hydrophilic cleaning of the glass surface was separately carried out by exposing it directly to Ar or Ar$/ \mathrm {O}_{2}$ plasma without using any chemical precursor. The hydrophobic coating layer observed by AFM technique was uniform and smooth with a root mean square roughness of 1.5 nm and a water contact angle (WCA) of around 100°. When oxygen was added to TMS, SiOSi and/or SiOC linkages were formed, which dominated the existence of Si(CHCH
2n
Si network, leading to decreasing the WCA. The mechanical strength of the coating layer was improved by lowering the TMS/APTES ratio, whereas the wettability decreased. The hydrophilic cleaning of the glass surface using Ar plasma showed that a short exposure time of about 10 s was very effective to make the surface hydrophilic without significant modification of the glass surfaces itself. The hydrophilic cleaning decreased the WCA from above 30° to nearly zero and the WCA was kept below 10° in 24 h in ambient air.