title: Auto-production of biosurfactants reverses the coffee ring effect in a bacterial system.
abstract: The deposition of material at the edge of evaporating droplets, known as the 'coffee ring effect', is caused by a radially outward capillary flow. This phenomenon is common to a wide array of systems including colloidal and bacterial systems. The role of surfactants in counteracting these coffee ring depositions is related to the occurrence of local vortices known as Marangoni eddies. Here we show that these swirling flows are universal, and not only lead to a uniform deposition of colloids but also occur in living bacterial systems. Experiments on Pseudomonas aeruginosa suggest that the auto-production of biosurfactants has an essential role in creating a homogeneous deposition of the bacteria upon drying. Moreover, at biologically relevant conditions, intricate time-dependent flows are observed in addition to the vortex regime, which are also effective in reversing the coffee ring effect at even lower surfactant concentrations.
authors.affiliation: Department of Chemistry, KU Leuven, University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
authors.forename: Wouter
authors.initials: W
authors.lastname: Sempels
authors.forename: Raf
authors.initials: R
authors.lastname: De Dier
authors.forename: Hideaki
authors.initials: H
authors.lastname: Mizuno
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Jan
authors.initials: J
authors.lastname: Vermant
mesh_terms: D000327:Adsorption; D018407:Bacterial Physiological Phenomena / Q000187:drug effects; D003198:Computer Simulation; D003890:Desiccation; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000378:metabolism*; D012212:Rheology / Q000187:drug effects; D013501:Surface-Active Agents / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors
chemical_list: D013501:Surface-Active Agents