Fig. 2.
Reduced pressure in channels due to evaporation. (A) Photograph of an open channel. (B) Microscopy image of an air–water meniscus at the end of an open channel. (C) Series of microscopy images depicting the imbibition of fluorescent oil into an open channel. For conditions with no evaporation (pw = pw,sat), no imbibition occurs; when evaporation is induced (pw < pw,sat), the oil is imbibed far into the biofilm. (D) Infrared thermograph of a biofilm on agar exposed to ambient air with RH = 56% and T = 21.5 °C reveals spatial differences in evaporative flux. (E) Illustration of evaporation from the surface of the film (blue arrows) that drives liquid flow throughout the agar and the biofilm. (Inset) Liquid-filled channels with high permeability for liquid flow exist beneath the biofilm and facilitate the flow of liquid in the xy plane. A gradient in evaporative flux (black arrows) could drive liquid flow within the channel (white arrow).