Auto-production of biosurfactants reverses the coffee ring effect in a bacterial system.
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ABSTRACT:
SUBMITTER: Sempels W
PROVIDER: S-EPMC3644097 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The coffee-ring effect, ubiquitously present in the drying process of aqueous droplets, impedes the performance of a myriad of applications involving precipitation of particle suspensions in evaporating liquids on solid surfaces, such as liquid biopsy combinational analysis, microarray fabrication, and ink-jet printing, to name a few. We invented the methodology of laser-induced differential evaporation to remove the coffee-ring effect. Without any additives to the liquid or any morphology modifications of the solid surface the liquid rests on, we have eliminated the coffee-ring effect by engineering the liquid evaporation profile with a CO2 laser irradiating the apex of the droplets. The method of laser-induced differential evaporation transitions particle deposition patterns from coffee-ring patterns to central-peak patterns, bringing all particles (e.g. fluorescent double strand DNAs) in the droplet to a designated area of 100 ?m diameter without leaving any stains outside. The technique also moves the drying process from the constant contact radius (CCR) mode to the constant contact angle (CCA) mode. Physical mechanisms of this method were experimentally studied by internal flow tracking and surface evaporation flux mapping, and theoretically investigated by development of an analytical model.
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Project description:The mechanism of droplet drying is a widely concerned fundamental issue since controlling the deposition morphology of droplet has significant influence on printing, biology pattern, self-assembling and other solution-based devices fabrication. Here we reveal a striking different kinetics-controlled deposition regime beyond the ubiquitous coffee-ring effect that suspended particles tend to kinetically accumulate at the air-liquid interface and deposit uniformly. As the interface shrinkage rate exceeds the particle average diffusion rate, particles in vertical evaporation flow will be captured by the descending surface, producing surface particle jam and forming viscous quasi-solid layer, which dramatically prevents the trapped particles from being transported to drop edge and results in uniform deposition. This simple, robust drying regime will provide a versatile strategy to control the droplet deposition morphology, and a novel direction of interface assembling for fabricating superlattices and high quality photonic crystal patterns.
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Project description:When a sessile droplet evaporates, coffee-ring effect drives the suspended particulate matters to the droplet edge, eventually forming a ring-shaped deposition. Because it causes a non-uniform distribution of solid contents, which is undesired in many applications, attempts have been made to eliminate the coffee-ring effect. Recent reports indicated that the coffee-ring effect can be suppressed by a mixture of spherical and non-spherical particles with enhanced particle-particle interaction at air-water interface. However, a model to comprehend the inter-particulate activities has been lacking. Here, we report a discrete element model (particle system) to investigate the phenomenon. The modeled dynamics included particle traveling following the capillary flow with Brownian motion, and its resultant 3D hexagonal close packing of particles along the contact line. For particles being adsorbed by air-water interface, we modeled cluster growth, cluster deformation, and cluster combination. We found that the suppression of coffee-ring effect does not require a circulatory flow driven by an inward Marangoni flow at air-water interface. Instead, the number of new cluster formation, which can be enhanced by increasing the ratio of non-spherical particles and the overall number of microspheres, is more dominant in the suppression process. Together, this model provides a useful platform elucidating insights for suppressing coffee-ring effect for practical applications in the future.
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Project description:Photocatalytic water purification is important for the degradation of organic pollutants, attracting intensive interests. Photocatalysts are preferred to be immobilized on a substrate in order to reduce the laborious separation and recycling steps. To get uniform irradiation, the photocatalysts are preferred to be even/uniform on the substrate without aggregation. Generally, the "coffee ring effect" occurs on the substrate during solvent evaporation, unfortunately resulting in the aggregation of the photocatalysts. This aggregation inevitably blocks the exposure of active sites, reactant exchange, and light absorption. Here, we reported a paper-based photocatalyst immobilization method to solve the "coffee ring" problem. We also used a "drop reactor" to achieve good photocatalytic efficiency with the advantages of large surface area, short diffusion lengths, simple operation, and uniform light absorption. Compared with the coffee ring type, the paper-based method showed higher water purification efficiency, indicating its potential application value in the future.
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Project description:Inkjet printing is of growing interest due to the attractive technologies for surface patterning. During the printing process, the solutes are transported to the droplet periphery and form a ring-like deposit, which disturbs the fabrication of high-resolution patterns. Thus, controlling the uniformity of particle coating is crucial in the advanced and extensive applications. Here, we find that sweet coffee drops above a threshold sugar concentration leave uniform rather than the ring-like pattern. The evaporative deposit changes from a ring-like pattern to a uniform pattern with an increase in sugar concentration. We moreover observe the particle movements near the contact line during the evaporation, suggesting that the sugar is precipitated from the droplet edge because of the highest evaporation and it causes the depinning of the contact line. By analyzing the following dynamics of the depinning contact line and flow fields and observing the internal structure of the deposit with a FIB-SEM system, we conclude that the depinned contact line recedes due to the solidification of sugar solution without any slip motion while suppressing the capillary flow and homogeneously fixing suspended particles, leading to the uniform coating. Our findings show that suppressing the coffee-ring effect by adding sugar is a cost-effective, easy and nontoxic strategy for improving the pattern resolution.
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Project description:A uniform deposition of the suspended particles in an evaporating droplet is necessary in many research fields. Such deposition is difficult to achieve, because the coffee-ring effect dominates the internal flow in a droplet. The present study adopts a biocompatible, surfactant-like polymer (Polyethylene glycol, PEG) to break the coffee-ring effect and obtain a relatively uniform deposition of the microparticles with yielding multi-ring pattern over a droplet area. Movements of the suspended particles in evaporating droplets and deposition patterns of them on a glass substrate were analyzed with microscopic images and video files. The PEG in the droplets successfully altered the coffee-ring effect because of the surface tension variation, which induced a centripetal Marangoni flow. Balancing these two phenomena apparently generated the Marangoni vortex. For PEG solution droplets, the pinning-depinning process during evaporation was periodically repeated and multiple rings were regularly formed. In conclusion, adding a surfactant-like viscous polymer in a droplet could provide a uniform coating of suspended particles, such as cells and various biomaterials, which would be essentially required for droplet assays of biomedical applications.
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Project description:The work is aimed to investigate the suitability of underutilized coffee cherry husk (CCH) for the production and optimization of bacterial cellulose (BC) by Gluconacetobacter hansenii UAC09 and to study the physico-mechanical properties of BC films. CCH extract was used as a carbon source in various concentrations along with other nutritional components such as nitrogen (corn steep liquor, urea) and additives (ethyl alcohol, acetic acid). Concentration of CCH extract at 1:1 (w/v) along with 8% (v/v) corn steep liquor, 0.2% (w/v) urea, combination of 1.5% ethyl alcohol and 1.0% (v/v) acetic acid resulted in the production of 5.6-8.2 g/L of BC. BC had tensile strength varying between 28.5 and 42.4 MPa. BC produced with CCH and Hestrin and Schramm (HS) media did not differ in structure as analyzed by FT-IR. Scanning electron microscopic studies indicated BC to contain reticulated network of fine fibers. Under optimized condition, based on the other additives, CCH produced more than three folds yield of BC (5.6-8.2 g/L) than control medium (1.5 g/L). This is the first report on the use of CCH for the production of BC and paved way for the utilization of organic wastes with pectin and high polyphenol content.
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Project description:A macroscopic evaporating water droplet with suspended particles on a solid surface will form a ring-like structure at the pinned contact line due to induced capillary flow. As the droplet size shrinks, the competition between the time scales of the liquid evaporation and the particle movement may influence the resulting ring formation. When the liquid evaporates much faster than the particle movement, coffee ring formation may cease. Here, we experimentally show that there exists a lower limit of droplet size, D(c), for the successful formation of a coffee ring structure. When the particle concentration is above a threshold value, D(c) can be estimated by considering the collective effects of the liquid evaporation and the particle diffusive motion within the droplet. For suspended particles of size approximately 100 nm, the minimum diameter of the coffee ring structure is found to be approximately 10 microm.
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Project description:The residual deposits usually left near the contact line after pinned sessile colloidal droplet evaporation are commonly known as a "coffee-ring" effect. However, there were scarce attempts to simulate the effect, and the realistic fully three-dimensional (3D) model is lacking since the complex drying process seems to limit the further investigation. Here we develop a stochastic method to model the particle deposition in evaporating a pinned sessile colloidal droplet. The 3D Monte Carlo model is developed in the spherical-cap-shaped droplet. In the algorithm, the analytical equations of fluid flow are used to calculate the probability distributions for the biased random walk, associated with the drift-diffusion equations. We obtain the 3D coffee-ring structures as the final results of the simulation and analyze the dependence of the ring profile on the particle volumetric concentration and sticking probability.
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