Shapes of surfactant-laden Taylor bubbles in a square microchannel

Experiments on contaminated Taylor flows in a square microchannel were carried out to investigate the effects of surfactant on the bubble shape in the nose and tail regions for different surfactant properties. The nose curvature was found to be proportional to the bubble length at low surfactant concentrations, while it was independent of the concentration at high concentrations. The rate of increase in the nose curvature at the former concentrations can be expressed in terms of the surface coverage ratio. The bubble velocity decreased with increasing the nose curvature, whereas the surface tension reduced by surfactant adsorption worked better to correlate the velocity data. The curvature of the bubble tail increased steeply at low concentrations as a consequence of the early coverage due to interfacial advection. The tail curvature also had a strong correlation with the surface coverage ratio.