Measurement of bubble size distribution in a gas–liquid foam using pulsed-field gradient nuclear magnetic resonance

Pulsed-field gradient nuclear magnetic resonance, previously used for measuring droplet size distributions in emulsions, has been used to measure bubble size distributions in a non-overflowing pneumatic gas–liquid foam that has been created by sparging propane into an aqueous solution of 1.5 g/l (5.20 mM) SDS. The bubble size distributions measured were reproducible and approximated a Weibull distribution. However, the bubble size distributions did not materially change with position at which they were measured within the froth. An analysis of foam coarsening due to Ostwald ripening in a non-overflowing foam indicates that, for the experimental conditions employed, one would not expect this to be a significant effect. It is therefore apparent that the eventual collapse of the foam is due to bubble bursting (or surface coalescence) rather than Ostwald ripening. This surface coalescence occurs because of evaporation from the free surface of the foam. An analytical solution for the liquid fraction profile for a certain class of non-overflowing pneumatic foam is given, and a mean bubble size that is appropriate for drainage calculations is suggested. Collated number distribution of bubble radii as a function of the height above the bubbly liquid–foam interface. The bold-dashed line is a Weibull distribution with α = 2.49 and β = 2.93. [Display omitted] ► Pulsed-Field Gradient Nuclear Magnetic Resonance has been used to measure the bubble size distribution in a non-overflowing pneumatic gas–liquid foam. ► The bubble size distributions are seen to approximately fit to the Weibull distribution. ► The bubble size distribution was seen to be approximately constant, indicating the changes in bubble size distribution due to inter-bubble gas diffusion (Ostwald ripening) and internal coalescence were insignificant. Pulsed-field gradient nuclear magnetic resonance, previously used for measuring droplet size distributions in emulsions, has been used to measure bubble size distributions in a non-overflowing pneumatic gas–liquid foam that has been created by sparging propane into an aqueous solution of 1.5 g/l (5.20 mM) SDS. The bubble size distributions measured were reproducible and approximated a Weibull distribution. However, the bubble size distributions did not materially change with position at which they were measured within the froth. An analysis of foam coarsening due to Ostwald ripening in a non-overflowing foam indicates that, for the experimental conditions em