The wetting nature of solid surfaces has numerous industrial applications ranging from enhanced oil (petroleum) recovery to microelectronics manufacturing. Wettability of an inert solid surface is its relative affinity towards a fluid in the presence of another immiscible or sparingly soluble fluid. Contact angle measurement is a widely used and accepted method for quantifying wettability of a surface. Alteration of inherently hydrophilic glass/quartz surface towards hydrophobic nature has many applications especially in microfluidics. The current study presents experimental procedures to obtain various degrees of controlled hydrophobicities on glass surfaces, corresponding air-water contact angle and surface roughness measurements using goniometer and atomic force microscopy, respectively. Chlorinated Polydimethylsiloxane (CM), Chlorinated Fluoroalkylmethylsiloxane (CF) and Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)Triethoxysilane (HT) with the respective experimental protocols were used to prepare the hydrophobic surfaces. First, all the glass substrates were rinsed in toluene. Then the silane (HT) was dissolved in 95:5 volume percent ethanol:water mixture and a 0.02% by volume glacial acetic acid and the siloxanes (CM and CF) were dissolved in toluene. Subsequently, the substrates were added to the respective solutions and left in the solutions for an hour for the surface chemical reactions to occur. To remove unreacted silane and siloxanes, the substrates were rinsed in ethanol, and n-hexane and ethanol, respectively. The untreated substrates were rinsed using n-hexane and ethanol. The treated and untreated substrates were dried in an oven at 105 °C. The average air-water contact angles measured on CM, CF, and HT hydrophobic surfaces were 90.8 ± 0.8°, 97.8 ± 0.4°, and 114.6 ± 0.75°, respectively, whereas on the untreated hydrophilic glass surface the contact angle was 33.91± 0.4°. The surface roughness data on the treated and untreated surfaces were found to be in the range of 1-5 nm. It is a known fact that on smooth surfaces such as used in this study, the maximum attainable air-water contact angle is 120°. So, the HT treated glass surface wettability alteration is close to the maximum possible hydrophobicity. From the above measurements, it can be observed that the contact angle values on treated glass surfaces are increased by 57° to 82° compared to the untreated surface depending on the coating material.

Preparation and quantification of various degrees of hydrophobic glass surfaces

256th National Meeting (2018)

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