Influence of wettability on pressure-driven bubble nucleation: A potential method for dissolved gas separation

Abstract

Bubble nucleation in supersaturated solutions is important for a wide range of natural and industrial processes. In this systematic experimental investigation, the effect of wettability on pressure-driven CO2 bubble nucleation from its aqueous supersaturated solution is studied. Glass surfaces of various degrees of hydrophobicities were prepared using respective surface chemical treatments with chlorinated polydimethylsiloxane (CM), chlorinated fluoroalkylmethylsiloxane (CF), and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (HT) for the bubble nucleation experiments. Contact angle and atomic force microscopy (AFM) measurements were conducted to quantify the wettability and surface roughness of the treated and untreated glass substrates. The average air-water contact angles of untreated, CM, CF and HT treated substrate were 33.9° ± 0.4°, 90.8° ± 0.8°, 97.8° ± 0.4° and 114.6° ± 0.75°, respectively. The average roughness (Ra) values of the untreated and treated surfaces were in the range of 1.1–18.9 nm. Supersaturated solutions of CO2 in water were prepared in a glass vial placed in a pressure cell by reducing the pressure in 100 mbar steps from the initial saturation pressure of 6000 mbar. The untreated (hydrophilic) surface did not promote bubble nucleation even when the pressure was reduced to atmospheric pressure. In contrast, the average bubble nucleation onset pressures for CM, CF and HT treated glass vials were 4840 ± 182, 5260 ± 134 and 5560 ± 89 mbar, respectively. These onset pressures for bubble nucleation were further confirmed by conducting the bubble nucleation experiments using CM, CF, and HT treated glass beads in hydrophilic vials.