According to Stokes’ Law, larger air bubbles rise through a liquid faster than smaller ones because their greater radius increases buoyancy relative to drag.  As bubbles collide and merge, they grow larger and escape the liquid more quickly.

Surfactants strongly influence this process.  AB-type surfactants tend to orient perpendicular to the air/water interface, with their hydrophilic chains extending into the liquid, creating steric barriers that prevent bubbles from coalescing.  In contrast, ABA-type surfactants typically orient more tangentially along the interface, providing less steric resistance and increasing the likelihood that bubbles will merge into larger ones.

This difference in molecular orientation can significantly affect foam stability and bubble size distribution.