Figure 2: Low concentrations of self-produced biosurfactants induce oscillatory flows in drying colonies.
From: Auto-production of biosurfactants reverses the coffee ring effect in a bacterial system
Plot of the time-dependent movement (horizontal axis, in seconds) of an individual bacterium of P. aeruginosa and its offset to the edge of the droplet, that is, the relative distance between the droplet edge and the position of the suspended bacterium (vertical axis, in μm). A recurrent back and forth movement can be observed, reminiscent of the phenomenon of ‘ebb and flood’. The outward capillary flow in the droplet and the subsequent local concentration buildup of the biosurfactant at the edge creates an opposing Marangoni stress of equal strength that counteracts the coffee ring effect.
