Abstract:A simplified model is developed, which allows us to perform computer simulations of the particles transport in an evaporating droplet with a contact line pinned to a hydrophilic substrate. The model accounts for advection in the droplet, diffusion and particle attraction by capillary forces. On the basis of the simulations, we analyze the physical mechanisms of forming of individual chains of particles inside the annular sediment. The parameters chosen correspond to the experiments of Park and Moon [Langmuir 2… Show more
“…6). This is natural if the adhesion to the substrate and capillary attraction between the particles are not taken into account [13,45,46]. Nevertheless, Fig.…”
Section: Resultsmentioning
confidence: 99%
“…To understand physical mechanisms of pattern formation in the process of sessile droplet drying is a fundamental task of crucial importance in various applications including biosensors, labs-on-chip, functional coatings, optoelectronics, biomedical applications, inkjet printing and many others [1,2]. Although issues of spatial structuring of deposition patterns from drying sessile drops have been extensively studied and the role of many effects has been clarified [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], no comprehensive analysis of pattern formation has been done so far, so evaporation of a droplet remains a complex phenomenon and there are a lot of questions that are unanswered yet. A prime example of such a controversial issue is the role of particle-particle, particle-substrate and particle-liquid-gas interface interactions in the presence of charged particles and counterions that are caused by electrolytic dissociation.…”
A model is developed for describing transport of colloidal silica particles in an evaporating aqueous sessile droplet on the electrified metal substrate in the presence of a solvent flow. The model takes into account the electric charge of colloidal particles and small ions produced by electrolytic dissociation of the active groups on the colloidal particles and water molecules. We employ a system of self-consistent Poisson and Nernst-Planck equations for electric potential and average concentrations of colloidal particles and ions with the respective boundary conditions. The developed model is used to make a first-principles numerical simulation of charged colloidal particle transport. We find that electric double layers can be destroyed by a sufficiently strong fluid flow such as Marangoni flow. Capillary fluid flows cannot destroy the electric double layer because they are much weaker than Marangoni flows.
“…6). This is natural if the adhesion to the substrate and capillary attraction between the particles are not taken into account [13,45,46]. Nevertheless, Fig.…”
Section: Resultsmentioning
confidence: 99%
“…To understand physical mechanisms of pattern formation in the process of sessile droplet drying is a fundamental task of crucial importance in various applications including biosensors, labs-on-chip, functional coatings, optoelectronics, biomedical applications, inkjet printing and many others [1,2]. Although issues of spatial structuring of deposition patterns from drying sessile drops have been extensively studied and the role of many effects has been clarified [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], no comprehensive analysis of pattern formation has been done so far, so evaporation of a droplet remains a complex phenomenon and there are a lot of questions that are unanswered yet. A prime example of such a controversial issue is the role of particle-particle, particle-substrate and particle-liquid-gas interface interactions in the presence of charged particles and counterions that are caused by electrolytic dissociation.…”
A model is developed for describing transport of colloidal silica particles in an evaporating aqueous sessile droplet on the electrified metal substrate in the presence of a solvent flow. The model takes into account the electric charge of colloidal particles and small ions produced by electrolytic dissociation of the active groups on the colloidal particles and water molecules. We employ a system of self-consistent Poisson and Nernst-Planck equations for electric potential and average concentrations of colloidal particles and ions with the respective boundary conditions. The developed model is used to make a first-principles numerical simulation of charged colloidal particle transport. We find that electric double layers can be destroyed by a sufficiently strong fluid flow such as Marangoni flow. Capillary fluid flows cannot destroy the electric double layer because they are much weaker than Marangoni flows.
“…This distance is determined by the value of the angle θ and the particle size itself. The boundary that particles cannot cross has been called the fixation radius 49 . This boundary corresponds to the radial coordinate, where the thickness of the liquid layer is about the particle size.…”
Section: Introductionmentioning
confidence: 99%
“…In this study, numerical calculations are performed using a mathematical model from Refs. 49,50 . Here, this model is adapted to a binary particle mixture.…”
Colloidal droplets are used in a variety of practical applications. Some applications require particles of different sizes. These include medical diagnostic methods, the creation of photonic crystals, the formation of supraparticles, and the production of membranes for biotechnology. Series of experiments have previously shown the possibility of particle separation by their size near the contact line. A mathematical model has been developed to describe this process. Bidispersed colloidal droplets evaporating on a hydrophilic substrate are taken into consideration. A particle monolayer is formed due to the small value of the contact angle near the periphery of such droplets. The shape of the resulting sediment is associated with the coffee ring effect. The model takes into account the particle diffusion and transfer with a capillary flow caused by liquid evaporation. Monte Carlo simulation of particle dynamics has been performed at several values of the solution concentration. The numerical results agree with the experimental observations, in which small particles accumulate closer toward the contact line than large particles.
“…As particles are immersed in the liquid, it is common that they are electrically charged or surrounded by an electrical layer, which would lead to the electrostatic force between particles and between particles and substrates. For particles captured by the descending interface, surface tension force would be exerted on the particles, which may lead to the capillary attraction between particles [119]. During the evaporation process, particles may touch the substrate under the flow transportation or gravitational sedimentation, then the friction force exists to hinder any further particle motion.…”
Section: Forces Acting On Suspended Particlesmentioning
Prof F. Duan provided the initial project direction and edited the manuscript drafts.At first, I would like to express my sincere gratitude and appreciation to my supervisor, Associate Professor Fei Duan. His patience, understanding, and support really help me a lot in dealing with the problems. Without his guidance during these four years, I will not be able to achieve the current progress. His efficient working style and constant encouragement always inspire me a lot.Second, I would like to sincerely express my special thankfulness to Dr. Xin Zhong for her direct help and guidance in my study. I acknowledge the help from Mr. Kian Soo ONG and Mr. (A*STAR) for fabricating the surfaces, his support is really important in my study. My gratitude also goes to my friends and colleagues, especially Dr. Wei Tong,
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