K. S. Kolegov

Bio: K. S. Kolegov is an academic researcher from Volga State University of Water Transport. The author has contributed to research in topics: Evaporation & Particle. The author has an hindex of 3, co-authored 11 publications receiving 40 citations. Previous affiliations of K. S. Kolegov include Landau Institute for Theoretical Physics & Astrakhan State University.

Joint effect of advection, diffusion, and capillary attraction on the spatial structure of particle depositions from evaporating droplets

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 22, 3506 (2006)LANGD50743-746310.1021/la053450j], where an annular deposition and snakelike chains of colloid particles have been identified. The annular sediment is formed by advection and diffusion transport. We find that the close packing of the particles in the sediment is possible if the evaporation time exceeds the characteristic time of diffusion-based ordering. We show that the chains are formed by the end of the evaporation process due to capillary attraction of particles in the region bounded by a fixing radius, where the local droplet height is comparable to the particle size. At the beginning of the evaporation, the annular deposition is shown to expand faster than the fixing radius moves. However, by the end of the process, the fixing radius rapidly outreaches the expanding inner front of the ring. The snakelike chains are formed at this final stage when the fixing radius moves toward the symmetry axis.

Simulation of Patterned Glass Film Formation in the Evaporating Colloidal Liquid under IR Heating

Abstract: The paper theoretically studies the method of evaporative lithography in combination with external infrared heating. This method makes it possible to form solid microstructures of the required relief shape as a result of evaporation of the liquid film of the colloidal solution under the mask. The heated particles are sintered easier, so there are no cracks in the obtained structure, unlike the structure obtained employing the standard method of evaporative lithography. The paper puts forward a modification of the mathematical model which allows to describe not only heat and mass transfer at the initial stage of the process, but also the phase transition of colloidal solution into glass. Aqueous latex is taken as an example. The resulting final form of solid film is in good agreement with the experimental data of other authors.

Joint effect of advection, diffusion, and capillary attraction on the spatial structure of particle depositions from evaporating droplets

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 22, 3506 (2006)LANGD50743-746310.1021/la053450j], where an annular deposition and snakelike chains of colloid particles have been identified. The annular sediment is formed by advection and diffusion transport. We find that the close packing of the particles in the sediment is possible if the evaporation time exceeds the characteristic time of diffusion-based ordering. We show that the chains are formed by the end of the evaporation process due to capillary attraction of particles in the region bounded by a fixing radius, where the local droplet height is comparable to the particle size. At the beginning of the evaporation, the annular deposition is shown to expand faster than the fixing radius moves. However, by the end of the process, the fixing radius rapidly outreaches the expanding inner front of the ring. The snakelike chains are formed at this final stage when the fixing radius moves toward the symmetry axis.

Nonuniform heating of a substrate in evaporative lithography

Abstract: The work is devoted to one method of structured sediments formation connected to evaporative lithography. Experiments were carried out with nonuniform evaporation of an isopropanol film containing polystyrene microspheres in a cylindrical cell. The local inhomogeneity of the vapor flux density was achieved due to the temperature gradient. A copper rod was mounted in the central part of the bottom of the cell for further heating. The thermocapillary flow resulting from the surface tension gradient due to the temperature drop transfers the particles that were originally at rest along the bottom of the cell. The effect of the initial thickness of the liquid layer on the height and area of the sediment formed in the central region of the cell is studied. The velocity was measured using PIV. A model describing the process at the initial stage is developed. The equations of heat transfer and thermal conductivity were used to define the temperature distribution in the liquid and the cell. The fluid flow was simulated by the lubrication approximation. The particle distribution was modeled using the convection-diffusion equation. The evaporation flux density was calculated using Hertz-Knudsen Eq. The dependence of the liquid viscosity on the particle concentration was described by Mooney's formula. Numerical results showed that the liquid film gradually becomes thinner in the central region, as the surface tension decreases with increasing temperature. The liquid flow is directed to the heater near the substrate. It transfers the particles to the center of the cell. The volume fraction of the particles increases over time in this region. The heat flow from the heater affects the geometry of the sediment for two reasons. First, the Marangoni flow velocity depends on the temperature gradient. Secondly, the decrease in film thickness near the heater depends on the temperature.

Lithographically-directed self-assembly of nanostructures

Abstract: The combination of lithography and self-assembly provides a powerful means of organizing solution-synthesized nanostructures for a wide variety of applications. We have developed a fluidic assembly method that relies on the local pinning of a moving liquid contact line by lithographically produced topographic features to concentrate nanoparticles at those features. The final stages of the assembly process are controlled first by long-range immersion capillary forces and then by the short-range electrostatic and Van der Waal's interactions. We have successfully assembled nanoparticles from 50 nm to 2 nm in size using this technique and have also demonstrated the controlled positioning of more complex nanotetrapod structures. We have used this process to assemble Au nanoparticles into pre-patterned electrode structures and have performed preliminary electrical characterization of the devices so formed. The fluidic assembly method is capable of very high yield, in terms of positioning nanostructures at each lithographically-defined location, and of excellent specificity, with essentially no particle deposition between features.

Evaporation of Sessile Droplets

Abstract: The evaporation of a sessile droplet of liquid is a complex and multifaceted fundamental topic of enduring scientific interest that is key to numerous physical and biological processes. As a result, in recent decades a considerable multidisciplinary research effort has been directed toward many different aspects of the problem. This review focuses on some of the insights that can be obtained from relatively simple mathematical models and discusses some of the directions in which the field may move in the future. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 55 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Disk-Ring Deposition in Drying a Sessile Nanofluid Droplet with Enhanced Marangoni Effect and Particle Surface Adsorption.

Abstract: The present study is to explore the central particle deposition from drying a sessile nanofluid droplet experimentally and theoretically. Normally, a pinned colloidal droplet dries into a coffee-ri...