Natural surfactant system: precursor flow in one-shot two-dimensional foam drainage

Area of Science:

• Colloid and Surface Science
• Foam Physics
• Rheology

Background:

• Foam drainage is crucial for foam stability, influenced by gravity, surface tension, and viscosity.
• Forced drainage experiments help elucidate liquid flow dynamics within foams.
• Understanding foam drainage is essential for applications ranging from detergents to enhanced oil recovery.

Purpose of the Study:

• To investigate two-dimensional (2D) forced drainage in foam stabilized by a natural surfactant from Sapindus mukorossi.
• To analyze the vertical and horizontal movement of draining liquid within the foam column.
• To characterize the flow behavior and identify novel flow phenomena.

Main Methods:

• Utilized a natural surfactant extracted from Sapindus mukorossi to create a foam column.
• Employed a 2D forced drainage technique, introducing liquid from the top to study flow dynamics.
• Visually monitored the draining liquid using a dye and measured light intensity to quantify liquid fraction.

Main Results:

• Observed that the draining wave front exhibits both vertical flow and horizontal spreading.
• The vertical front's movement followed a power law, indicative of Poiseuille flow, similar to synthetic surfactants.
• Liquid fraction distribution was Gaussian horizontally but showed an asymmetric, distorting Gaussian vertically after 10 seconds, suggesting dual flow mechanisms.

Conclusions:

• The study demonstrates novel 2D forced drainage behavior in natural Sapindus mukorossi surfactant foam.
• The observed asymmetric vertical distribution and distortion indicate the simultaneous occurrence of two distinct liquid flow types.
• These dual flow mechanisms in foam drainage are unprecedented and warrant further investigation to understand their underlying causes.