Bubble formation in complex fluids using an orifice in throat arrangement

• Pinch-off process in swelled biopolymer from natural sources using a novel co-flow device.
• Effect of the liquid to gas flow ratio.
• Deviations from unimodal size distribution.
• The self-alignment of mono/bidisperse bubbles in a cluster.
• Retained alignment of bubbles through crosslinking and drying of the continuous phase.

During the co-flow of a gas and a surrounding liquid film, the inner thread of gas breaks due to Rayleigh instability, and produces a series of bubbles in the embedding liquid. This article describes a co-flow arrangement that generates bubbles to form a hydrogel scaffold. The flow arrangement utilizes the “orifice in throat” configuration for a second squeeze on the bubble that resulted in further split into the bubbles of smaller size. Aqueous solutions of two biocompatible polymers were considered as the continuous phases. These are alginate and chitosan. The mechanism of bubble formation was studied under a microscope. The bubbles were collected on a petridish in a thin layer of liquid. The images demonstrate the self-alignment of bubbles in a monolayer, without coalescence, or shrinkage. An edge detection algorithm was utilized to compute the bubble size. The cumulative frequency of less than type as a function of the bubble diameter was fitted to Gompertz function. The derivative of this function provided the bubble size distribution. Multiple functions were considered for a single curve to explore possibilities other than unimodal distributions. The bubble growth and disengagement processes, and consequent dispersion in bubble size were compared for the two gel systems. The effect of heterogeneity in the gel formulation on the bubble generation process associated bifurcations was reviewed. Sprinkling of the cross-linker solution on the scaffold resulted in the formation of a robust free-resting gel film, without any alteration of the mutual alignment of bubbles. The vacuum-dried gel film was further studied under a scanning electron microscope.