Insights into Transient Dynamics of Bacteria-Laden Liquid Bridges

We study the evaporation mechanics and precipitate characterization of the bacteria-laden liquid bridge using experimental and theoretical analysis. Aqueous suspensions of motile and nonmotile <i>Salmonella typhimurium</i> and <i>Pseudomonas aeruginosa</i> typically found in contaminated food and water were used in liquid bridge configuration between hydrophilic substrates. Using the inverse logarithmic evaporation flux model, we study the liquid bridge volume regression using cylindrical and catenoid volume models for various confinement distances. We show that for all confinement distances the volume regression is linear on normalizing both volume and time as in the case of a pure sessile drop. However, in normalized volume and dimensional time space we observe some nonlinearities as the total evaporation time scales non linearly with the confinement distance. The nonlinearities found were captured using the catenoid model. The cylindrical volume model fails to capture the regression trend, whereas the catenoid model conforms to the experimental volume regression data at all confinement distances and the transient liquid bridge interface evolution profile at a high confinement distance. Further, we also study the precipitate pattern and bacterial distribution using micro/nanocharacterization techniques. We show that the average precipitate pattern for both sessile and higher confinement distances resembles coffee-ring-type deposits, although the underlying bacterial distribution differs. For lower confinement, we observe a pattern resulting from a combination of the coffee-ring effect, stick-slick motion, and thin film instability. The reduction in confinement distance causes an altered bacterial agglomeration, resulting in a multipattern network instead of a single circumferential edge deposition. We show that the aerial size of motile bacteria increases with decreasing confinement, whereas the size of nonmotile bacteria remains constant in the precipitate. These findings have a crucial understanding of the establishment of pathogenesis in humans in hospital settings.