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11: a-c. Images of a region within 40 µm of the drop contact line, taken at time t/t F inal = 0.5, for suspensions of spheres (a), suspensions of ellipsoids with α = 3.5 (b), and ellipsoids with α = 3.5 mixed with a surfactant (SDS) at 0.2% by weight. While spheres pack closely at the contact line, ellipsoids form loosely packed structures. Added surfactant lowers the surface tension of the drop, making ellipsoidal particles pack closely at the contact line, thus restoring the coffee ring effect. For a and b, pictures of the entire drop after evaporation are shown and the magnified region is indicated. d,e. Confocal projections of suspension of ellipsoids (α = 2.5) and spheres (d and e, respectively) onto the z-r plane in cylindrical coordinates. While spheres are efficiently transported to the contact line, ellipsoids sit at the air-water interface.
Source publication
This thesis describes experiments that utilize colloids to explore nonequilibrium phenomena. Specifically, the deposition of particles during evaporation and the glass transition are explored.
In the first set of experiments, we found that particle shape has a profound effect on particle deposition. We evaporated drops of colloidal suspensions cont...
Citations
... For a sessile drop, the fluid flows radially outwards to replace the evaporated fluid at the base edge of the drop, maintaining a constant radius thus leading to the commonly seen coffee ring. 35,36 The pinning of the contact line ensures outward capillary flow that helps in carrying the material toward the edge of the pinned surface, as represented in the literature. [37][38][39][40] Moreover, capillary flow creates a thick outer ring at its maximum spread when the droplet impinges at a certain velocity for which the viscosity of the base fluid medium is accountable for transporting particles toward the contact line. ...
Despite extensive studies on kinematic features of impacting drops, the effect of mechanical stress on desiccated bacteria-laden droplets remains unexplored. In the present study, we unveiled the consequences of the impaction of bacteria-laden droplets on solid surfaces and their subsequent desiccation on the virulence of an enteropathogen Salmonella Typhimurium (STM). The methodology elucidated the deformation, cell-cell interactions, adhesion energy, and roughness in bacteria induced by impact velocity and low moisture due to evaporation. Salmonella retrieved from the dried droplets were used to understand fomite-mediated pathogenesis. The impact velocity-induced mechanical stress deteriorated the in vitro viability of Salmonella. Interestingly, an uninterrupted bacterial proliferation was observed in macrophages at higher mechanical stress. Wild-type Salmonella under mechanical stress induced the expression of phoP while infecting macrophages. The inability of STM ΔphoP to grow in nutrient-rich dried droplets signifies the role of phoP in sensing the mechanical stress and maintaining the virulence of Salmonella.
... The copyright holder for this preprint this version posted May 29, 2022. 19,20 . Moreover, capillary flow creates a thick outer ring at its maximum spread when the droplet is impacted at a certain velocity for which the viscosity of the base fluid medium is accountable for carrying the particle towards the contact line 21 . ...
Droplet impacts on various surfaces play a profound role in different bio-physiological processes and engineering applications. The current study opens a new realm that investigates the plausible effect of impact velocities on bacteria-laden droplets against a solid surface. We unveiled the alarming consequences of Salmonella Typhimurium (STM) laden drop, carrying out the in vitro and intracellular viability of STM to the impact Weber numbers ranging from 100-750. The specified Weber number range mimics the velocity range occurring during the respiratory processes, especially the airborne dispersion of drops during cough. A thick ring of bacterial deposition was observed in all cases irrespective of impacting velocity and the nutrient content of the bacterial medium. The mechanical properties of the bacterial deposit examined using Atomic Force Microscopy reveals the deformation of bacterial morphology, cushioning effect and adhesion energy to determine the cell-cell interactions. The impact velocity induces the shear stress onto the cell walls of STM, thereby deteriorating the in vitro viability. However, we found that even with compromised in vitro viability, Salmonella retrieved from deposited patterns impacted at higher velocity revealed an increased expression of phoP (the response regulator of the PhopQ two-component system) and uninterrupted intracellular proliferation in macrophages. The inability of STM ΔphoP growth in nutrient-rich dried droplets to the subjected impact velocities signifies the predominant role of phoP in maintaining the virulence of Salmonella during desiccation stress. Our findings open a promising avenue for understating the effect of bacteria-laden drop impact and its role in disease spread.
Abstract Figure
... In the second stage of evaporation, capillary and Marangoni flows compete to establish the flow inside the drop, as shown in Stage II, Figure 9. Without measurements of the flow inside the drop, which would be technically difficult, it is unfathomable to discern the details of this process, but some aspects can be inferred from the subsequent evaporation phase. In the third stage of evaporation, in droplets containing Clonazepam, Methotrexate, and Ciprofloxacin, the capillary flows overcome Marangoni flows, see Stage III in Figure 9. Here, evaporation at the edge of the droplet induces outwards flow that increases the concentration of compounds at the rim of the drop (the coffee ring) ring [42][43][44]. ...
The quality control of medicines guarantees the effectiveness of treatments for diseases. We explore the use of texture analysis of patterns in dried droplets as a tool to readily detect both impurities and changes in drug concentration. Four types of medicines associated with different routes of administration were analyzed: Methotrexate, Ciprofloxacin, Clonazepam, and Budesonide. We use NaCl and a hot substrate at 63 ∘C to promote aggregate formation and to reduce droplet drying time. Depending on the medicine, optical microscopy reveals different complex aggregates such as circular to oval splatters, fern-like islands, crown shapes, crown needle-like and bump-like patterns as well as dendritic branched and star-like crystals. We use some physical features of the stains (as the stain diameter and superficial area) and gray level co-occurrence matrix (GLCM) to characterize patterns of dried droplets. Finally, we show that structural analysis of stains can achieve 95% accuracy in identifying medicines with 30% water dilution, while it achieves 99% accuracy in detecting drugs with 10% other substances.
... For instance, evaporation of droplet is a recurrent technique which allows different pattern formation of particles by evaporation of solvent in an open system. Convection flow (capillary and Marangoni flow) and different forces (collision, electrostatic interaction caused by the charges of the molecules, adhesion between the molecules and substrate) are responsible for the ultimate pattern formation by drying of the droplet studied so far for many synthetic as well as biomolecules [16][17][18][19][20][21][22][23][24][25][26]. Here, we report formation of spherulites from tubulins through polymerization into MTs by heating under water evaporation in a droplet like open system. ...
... The Maltese Crosses pattern formation in the droplets was observed at a certain tubulin concentration 45 μM which favored the velocity of growth of polymerization of tubulins into MTs [34,36] and formed spherulite like structures at the edge of the droplet. The radially aligned structure formation at the edge of the droplet confirmed the replacement of the solute particles (tubulin dimes) by the capillary flow like convection flow similar to the so-common coffee ring effect at the elevated temperature [16][17][18][19] (Fig 2C). With further increasing the concentration of tubulin, nucleation points of spherulites appeared from the center of the droplet after the drying of the edge which indicates uniform deposition of tubulin dimers and consequently polymerized MTs. ...
... The mechanism of MT spherulite formation in the evaporating droplet is a very complicated one that cannot be elucidated by a single step. The evaporation of the droplet of tubulin solution indeed agrees with the so-called phenomenon coffee ring effect [16,20,22] by the convection flow and it may have some effect on the directional alignment of MTs. But the formation of radially aligned spherulite structure by the polymerized MTs still remains elusive. ...
We report the formation of spherulites from droplets of highly concentrated tubulin solution via nucleation and subsequent polymerization to microtubules (MTs) under water evaporation by heating. Radial alignment of MTs in the spherulites was confirmed by the optical properties of the spherulites observed using polarized optical microscopy and fluorescence microscopy. Temperature and concentration of tubulins were found as important parameters to control the spherulite pattern formation of MTs where evaporation plays a significant role. The alignment of MTs was regulated reversibly by temperature induced polymerization and depolymerization of tubulins. The formation of the MTs patterns was also confirmed at the molecular level from the small angle X-ray measurements. This work provides a simple method for obtaining radially aligned arrays of MTs.
... The morphology of the deposit of a protein mixture solution is a consequence of the competition between gelation and desiccation kinetics [9]. Faster evaporation at the edge of the droplet produces a radial flow that increases the protein concentration generating a coffee ring effect [39,40,14], see Fig. 6a and b. After that, the gelation process appears forming a rim. ...
... During this process, the capillary flows move radially outwards to compensate the loss of mass because the evaporation of water molecules occurs mostly at the edge of the droplet. Indeed, this transport mechanism generated the so called "coffee ring effect" [14,39,40]. Marangoni flows, on the other hand, are produced by surfactants and temperature gradients. ...
Patterns formed by the evaporation of a drop containing biological molecules have provided meaningful information about certain pathologies. In this context, several works propose the study of protein solutions as a model to understand the formation of deposits of biological fluids. Generally, dry droplets of proteins in a saline solution create complex aggregates. Here, we present an experimental study on the formation of patterns produced by the evaporation of droplet suspensions containing a protein binary mixture. We explore the structural aspect of such deposits by using optical and atomic force microscopy. We found that salt is unnecessary for the formation of complex structures such as crystal clusters, dendritic and undulated branches, and interlocked chains. Such structural features allow us to differentiate among protein binary mixtures. Finally, we discuss the potential use of this finding to reveal the presence of a protein suspensions, the folded and unfolded state of a protein, as well as their structural changes.
... Dans la majorité des systèmes, les trois conditions sont réalisées, c'est-à-dire que l'effet tache de café est le mode de séchage auquel on doit s'attendre lors du séchage d'une goutte de suspension du fait de l'immobilisation de la ligne de contact, généralement due à la fixation d'une certaine quantité de particules sur le substrat [156]. ...
La formulation d'une encre diélectrique et son dépôt par impression jet d'encre en vue de la fabrication de modules LTCC ont été étudiés, dans le cadre du projet européen SPrinTronics. Les verrous technologiques de la formulation de l'encre ont pu être levés afin d'ajuster ses caractéristiques au procédé. Pour cela, les mécanismes d'hydrolyse de la poudre, d'adsorption/désorption du dispersant et de fragmentation de la poudre ont été étudiés. Il a été mis en évidence la complexité d'obtenir à la fois une grande stabilité et une granulométrie fine. Les tests préliminaires d'impression ont révélé que les différentes stratégies influencent fortement la planéité des plans. Notamment, il est possible de minimiser la rugosité de surface de plans diélectriques imprimés par jet d'encre en maîtrisant la nature de la maille, l'interpénétration des gouttes et la stratégie de remplissage de la maille. Ces différents travaux sont prometteurs quand à l'industrialisation futur de la méthode. Cependant, les efforts doivent être poursuivis afin de mettre au point des véhicules de test.
The deposit patterns derived from droplet evaporation allow current development of medical tests and new strategies for diagnostic in patients. For such purpose, the development and implementation of algorithms capable of characterizing and differentiating deposits are crucial elements. We report the study of deposit patterns formed by the droplet evaporation of binary mixtures of proteins containing NaCl. Optical microscopy reveals aggregates such as tip arrow-shaped, dendritic and semi-rosette patterns, needle-like and scalloped lines structures, as well as star-like and prism-shaped salt crystals. We use the first-order statistics (FOS) and gray level co-occurrence matrix (GLCM) to characterize the complex texture of deposit patterns. Three significant findings arise from this analysis: first, the FOS and GLCM parameters structurally characterize protein deposits. Secondly, they conform to simple exponential laws that change as a function of the NaCl concentration. Finally, the parameters are capable of revealing the different structural changes that occur during the droplet evaporation
The objective of this review is to investigate different deposition patterns from dried droplets of a range of fluids: paints, polymers and biological fluids. This includes looking at mechanisms controlling the patterns and how they can be manipulated for use in certain applications such as medical diagnostics and nanotechnology. This review introduces the fundamental properties of droplets during evaporation. These include profile evolution (constant contact angle regime (CCAR) and constant radius regime (CRR)) and the internal flow (Marangoni and Capillary flow (Deegan et al. [22])). The understanding of these processes and the basic physics behind the phenomenon are crucial to the understanding of the factors influencing the deposition patterns. It concludes with the applications that each of these fluids can be used in and how the manipulation of the deposition pattern is useful. The most commonly seen pattern is the coffee-ring deposit [27] which can be seen frequently in real life from tea/coffee stains and in water colour painting. This is caused by an outward flow known as capillary flow which carries suspended particles out to the edge of the wetted area. Other patterns that were found were uniform, central deposits and concentric rings which are caused by inward Marangoni flow. Complex biological fluids displayed an array of different patterns which can be used to diagnose patients.
