Detecting microorganisms producing surface active compounds in mangrove sediments in São Luís, Maranhão

Mangroves are areas of sediment transitions, favoring the cycling of materials associated with high concentration of microorganisms, presenting vulnerability to anthropogenic actions. The objective of this study was to evaluate the ability of microbiota in mangrove sediments of the Anil River, in the city of São Luís, Maranhão. To produce surface active compounds (SACs), samples were collected according to the EMBRAPA methodology by inoculating them in the Bushnell Haas medium, with carbon sources varying at 3% (v/v). From the production obtained, the supernatants of each culture were submitted to E24 analysis, drop spreading, thermal stability/pressure and pH variation. The SAC-producing species were identified using the MALDI-QTOF MS method. The producing species were identified as Serratia marcescens (2), Ochrobactrum spp. (3). E24 values ranged from 33% to 48% yield, with stability increase after autoclaving of 3% to 6% and of 17% for basic pH ranges, demonstrating the feasibility of using regional microorganisms present in mangroves to produce SACs from different carbon sources, as they have good rates of emulsification and stability to the diverse environmental factors.

Capillary ripples in thin viscous films

Capillary ripples in thin viscous films are important features of coating and lubrication flows. Here, we present experiments based on digital holographic microscopy, measuring with nanoscale resolution the morphology of capillary ripples ahead of a viscous drop spreading on a prewetted surface. Our experiments reveal that upon increasing the spreading velocity, the amplitude of the ripples first increases and subsequently decreases. Above a critical spreading velocity, the ripples even disappear completely and this transition is accompanied by a divergence of the ripple wavelength. These observations are explained quantitatively using linear wave analysis, beyond the usual lubrication approximation, illustrating that new phenomena arise when the capillary number becomes of the order of unity.

Enhancing the spreading dynamics of oil drops over nanofiber substrates

The spreading dynamics of small oil drops over nanofiber layers has been investigated to improve the oil spill management process. Although liquid transport studies have been used to compare different substrates, the actual effect of the fibrous substrate structure has not been precisely investigated. Nanofiber substrate structures consist of micro- and nanocapillaries that vary in diameter and length and are interconnected in a complex manner. Migration of a liquid from one layer to another as well as on the same layer is an important part of the sorption process in nanofiber substrate structures. In this work, the problem under investigation provides spreading small oil drops over a thin porous layer nanofiber until saturation. An experimental evolution describing the drop spreading has been deduced, which shows the speed of spread of the oil drop is significantly affected by the substrate areal weight. The oil drop area over a dry porous layer seems to be caused by the interchange of two spreading velocities, one over the layers and the other penetration of the oil drop through the pores of the substrate. The higher the oil spreading speed, the lower the permeation of the oil into the porous nanofiber substrate and vice versa. To increase the absorption of the nanofiber substrate, adding a nonwoven thin film to cover the nanofiber layers was studied. It was revealed that the presence of such film significantly accelerates the oil-drop spreading speed by up to 300% and reduces the overall time of the oil drop's life.