Bubble Growth from Submerged Orifice Plates: Part 1- Decoupling Interfacial Tension and Surface Wettability Effects

Liquid-gas interfacial tension, substrate wettability, and upstream gas-chamber volume strongly affect the departure size and the growth dynamics of a bubble emanating from an orifice plate submerged in a quiescent liquid pool. These are experimentally investigated in two companion papers. Part 2 examines the gas-chamber volume influence on the growth dynamics. In Part 1 (this paper), to decouple and understand the effects of surface tension and wettability, bubble growth-dynamics in aqueous surfactant solutions and binary mixtures of ethanol-water are studied. Seven different substrates with contact angles ranging from 43° to 128° are used. High-speed videography and precision digital image processing were utilized to experimentally analyze bubble growth. Experiments using ethanol-water mixtures with surface tension varying between 35.5 and 72.5 mN/m revealed that there is a critical liquid-gas interfacial tension (∼46 mN/m) below which no de-wetting is observed on both hydrophobic and hydrophilic surfaces, and the bubble departure size is independent of surface wettability. For surface tension greater than the critical surface tension, bubble base spreads on hydrophobic substrates giving rise to larger bubble sizes at departure. Likewise, using six different concentrations of Triton X-305 solutions, the critical contact angle was obtained (∼64°) below which no de-wetting of bubble base is observed. A regime map is provided that demarcates the capillary-like behavior from the region where surface de-wetting occurs.