The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Victor Starov - One of the best experts on this subject based on the ideXlab platform.
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hysteresis of the Contact Angle of a meniscus inside a capillary with smooth homogeneous solid walls
Langmuir, 2016Co-Authors: I V Kuchin, Victor StarovAbstract:A theory of Contact Angle hysteresis of a meniscus inside thin capillaries with smooth, homogeneous solid walls is developed in terms of surface forces (disjoining/conjoining pressure isotherm) using a quasi-equilibrium approach. The disjoining/conjoining pressure isotherm includes electrostatic, intermolecular, and structural components. The values of the static Receding θr, advancing θa, and equilibrium θe Contact Angles in thin capillaries were calculated on the basis of the shape of the disjoining/conjoining pressure isotherm. It was shown that both advancing and Receding Contact Angles depend on the capillary radius. The suggested mechanism of the Contact Angle hysteresis has a direct experimental confirmation: the process of Receding is accompanied by the formation of thick β-films on the capillary walls. The effect of the transition from partial to complete wetting in thin capillaries is predicted and analyzed. This effect takes place in very thin capillaries, when the Receding Contact Angle decrea...
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Evaporation of Droplets of Surfactant Solutions
2016Co-Authors: Sergey Semenov, Victor Starov, Hezekiah Agogo, Anna Trybala, Nina Kovalchuk, Francisco Ortega, Ramón G. Rubio, Manuel G. VelardeAbstract:The simultaneous spreading and evaporation of droplets of aqueous trisiloxane (superspreader) solutions onto a hydrophobic substrate has been studied both experimentally, using a video-microscopy technique, and theoretically. The experiments have been carried out over a wide range of surfactant concentration, temperature, and relative humidity. Similar to pure liquids, four different stages have been observed: the initial one corresponds to spreading until the Contact Angle, θ, reaches the value of the static advancing Contact Angle, θad. Duration of this stage is rather short, and the evaporation during this stage can be neglected. The evaporation is essential during the next three stages. The next stage after the spreading, which is referred to herein as the first stage, takes place at constant perimeter and ends when θ reaches the static Receding Contact Angle, θr. During the next, second stage, the perimeter decreases at constant Contact Angle θ = θr for surfactant concentration above the critical wetting concentration (CWC). The static Receding Contact Angle decreases during the second stage for concentrations below CWC because the concentration increases due to the evaporation. During the final stage both the perimeter and the Contact Angle decrease. In what follows, we consider only the longest stages I and II. The developed theory predicts universal curves for the Contact Angle dependency on time during the first stage, and for the droplet perimeter on time during the second stage. A very good agreement between theory and experimental data has been found for the first stage of evaporation, and for the second stage for concentrations above CWC; however, some deviations were found for concentrations below CWC
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hysteresis of Contact Angle of sessile droplets on smooth homogeneous solid substrates via disjoining conjoining pressure
Langmuir, 2015Co-Authors: I V Kuchin, Victor StarovAbstract:A theory of Contact Angle hysteresis of liquid droplets on smooth, homogeneous solid substrates is developed in terms of the shape of the disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all Contact Angles, θ, in the range θr < θ < θa, which are different from the unique equilibrium Contact Angle θ ≠ θe, correspond to the state of slow "microscopic" advancing or Receding motion of the liquid if θe < θ < θa or θr < θ < θe, respectively. This "microscopic" motion almost abruptly becomes fast "macroscopic" advancing or Receding motion after the Contact Angle reaches the critical values θa or θr, correspondingly. The values of the static Receding, θr, and static advancing, θa, Contact Angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining/conjoining pressure isotherm. It is shown now that (i) both advancing and Receding Contact Angles of a droplet on a on smooth, homogeneous solid substrate can be calculated based on shape of disjoining/conjoining pressure isotherm, and (ii) both advancing and Receding Contact Angles depend on the drop volume and are not unique characteristics of the liquid-solid system. The latter is different from advancing/Receding Contact Angles in thin capillaries. It is shown also that the Receding Contact Angle is much closer to the equilibrium Contact Angle than the advancing Contact Angle. The latter conclusion is unexpected and is in a contradiction with the commonly accepted view that the advancing Contact Angle can be taken as the first approximation for the equilibrium Contact Angle. The dependency of hysteresis Contact Angles on the drop volume has a direct experimental confirmation.
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Evaporation of droplets of surfactant solutions
2013Co-Authors: Sergey Semenov, Victor Starov, Hezekiah Agogo, Anna Trybala, Nina Kovalchuk, Francisco Ortega, Ramon Rubio, M.g. VelardeAbstract:The simultaneous spreading and evaporation of droplets of aqueous trisiloxane (super-spreader) solutions onto a hydrophobic substrate has been studied both experimentally, using a video-microscopy technique, and theoretically. The experiments have been carried out over a wide range of surfactant concentration, temperature and relative humidity. Similar to pure liquids, four different stages have been observed: the initial one corresponds to spreading till the Contact Angle, , reaches the value of the static advancing Contact Angle, θad. Duration of this stage is rather short and the evaporation during this stage can be neglected. The evaporation is essential during next three stages. The next stage after the spreading, which is referred to below as the first stage, takes place at constant perimeter and ends when reaches the static Receding Contact Angle, θr. During the next, second stage, the perimeter decreases at constant Contact Angle =θr for surfactant concentration above critical wetting concentration (CWC). The static Receding Contact Angle decreases during the second stage for concentrations below CWC because the concentration increases due to the evaporation. During the final stage both the perimeter and the Contact Angle decrease till the drop disappears. Below we consider only the longest stages one and two. The developed theory predicts universal curves for the Contact Angle dependency on time during the first stage, and for the droplet perimeter on time during the second stage. A very good agreement between theory and experimental data has been found for the first stage of evaporation, and for the second stage for concentrations above CWC, however, some deviations were found for concentrations below CWC
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evaporation of sessile water droplets universal behaviour in presence of Contact Angle hysteresis
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011Co-Authors: Sergey Semenov, Victor Starov, Ramon G Rubio, Hezekiah Agogo, Manuel G VelardeAbstract:A theory is presented, which describes the diffusion limited evaporation of sessile water droplets in presence of Contact Angle hysteresis. Theory describes two stages of evaporation process: (I) evaporation with a constant radius of the droplet base; and (II) evaporation with a constant Contact Angle. During stage (I) the Contact Angles decreases from static advancing Contact Angle to static Receding Contact Angle. During stage (II) the Contact Angle remains equal to the static Receding Contact Angle. Universal dependences are deduced for both evaporation stages. Obtained universal curves are validated against available in the literature experimental data.
Li-jen Chen - One of the best experts on this subject based on the ideXlab platform.
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fabrication of sticky and slippery superhydrophobic surfaces via spin coating silica nanoparticles onto flat patterned substrates
Nanotechnology, 2011Co-Authors: Li-jen ChenAbstract:Silica nanoparticles were spin-coated onto a flat/patterned (regular pillar-like) substrate to enhance the surface roughness. The surface was further modified by a self-assembled fluorosilanated monolayer. The advancing/Receding Contact Angle and sliding Angle measurements were performed to determine the wetting behavior of a water droplet on the surface. It is interesting to find that a transition from a Wenzel surface to a sticky superhydrophobic surface is observed due to the spin-coating silica nanoparticles. A slippery superhydrophobic surface can be further obtained after secondary spin-coating with silica nanoparticles to generate a multi-scale roughness structure. The prepared superhydrophobic substrates should be robust for practical applications. The adhesion between the substrate and nanoparticles is also examined and discussed.
I V Kuchin - One of the best experts on this subject based on the ideXlab platform.
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hysteresis of the Contact Angle of a meniscus inside a capillary with smooth homogeneous solid walls
Langmuir, 2016Co-Authors: I V Kuchin, Victor StarovAbstract:A theory of Contact Angle hysteresis of a meniscus inside thin capillaries with smooth, homogeneous solid walls is developed in terms of surface forces (disjoining/conjoining pressure isotherm) using a quasi-equilibrium approach. The disjoining/conjoining pressure isotherm includes electrostatic, intermolecular, and structural components. The values of the static Receding θr, advancing θa, and equilibrium θe Contact Angles in thin capillaries were calculated on the basis of the shape of the disjoining/conjoining pressure isotherm. It was shown that both advancing and Receding Contact Angles depend on the capillary radius. The suggested mechanism of the Contact Angle hysteresis has a direct experimental confirmation: the process of Receding is accompanied by the formation of thick β-films on the capillary walls. The effect of the transition from partial to complete wetting in thin capillaries is predicted and analyzed. This effect takes place in very thin capillaries, when the Receding Contact Angle decrea...
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hysteresis of Contact Angle of sessile droplets on smooth homogeneous solid substrates via disjoining conjoining pressure
Langmuir, 2015Co-Authors: I V Kuchin, Victor StarovAbstract:A theory of Contact Angle hysteresis of liquid droplets on smooth, homogeneous solid substrates is developed in terms of the shape of the disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all Contact Angles, θ, in the range θr < θ < θa, which are different from the unique equilibrium Contact Angle θ ≠ θe, correspond to the state of slow "microscopic" advancing or Receding motion of the liquid if θe < θ < θa or θr < θ < θe, respectively. This "microscopic" motion almost abruptly becomes fast "macroscopic" advancing or Receding motion after the Contact Angle reaches the critical values θa or θr, correspondingly. The values of the static Receding, θr, and static advancing, θa, Contact Angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining/conjoining pressure isotherm. It is shown now that (i) both advancing and Receding Contact Angles of a droplet on a on smooth, homogeneous solid substrate can be calculated based on shape of disjoining/conjoining pressure isotherm, and (ii) both advancing and Receding Contact Angles depend on the drop volume and are not unique characteristics of the liquid-solid system. The latter is different from advancing/Receding Contact Angles in thin capillaries. It is shown also that the Receding Contact Angle is much closer to the equilibrium Contact Angle than the advancing Contact Angle. The latter conclusion is unexpected and is in a contradiction with the commonly accepted view that the advancing Contact Angle can be taken as the first approximation for the equilibrium Contact Angle. The dependency of hysteresis Contact Angles on the drop volume has a direct experimental confirmation.
Elmar Bonaccurso - One of the best experts on this subject based on the ideXlab platform.
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influence of surfactant transport suppression on dynamic Contact Angle hysteresis
Colloid and Polymer Science, 2013Co-Authors: Daniela Fell, Ngamjarassrivichai Pawanrat, Elmar Bonaccurso, Hansjuergen Butt, Gunter K AuernhammerAbstract:The influence of local and nonlocal transport processes of cetyltrimethylammonium bromide (CTAB) molecules on dynamic Contact Angles and Contact Angle hysteresis was studied in a rotating drum setup. The influence of long-range surfactant transport was analyzed by hindering selectively the surface or the bulk transport via movable barriers. With increasing hindrance of the surfactant transport, the Receding Contact Angle decreased at all withdrawing velocities in the presence of CTAB. The control experiment with pure water was unaffected by the presence of the barriers. Dynamic Contact Angles are, therefore, not only influenced by short-range effects like Marangoni stresses close to the Contact line, but also by long-range transport processes (like diffusion and advection) between the regions close to the Receding and advancing Contact lines.
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evaporation control of sessile water drops by soft viscoelastic surfaces
Soft Matter, 2012Co-Authors: Marcus C Lopes, Elmar BonaccursoAbstract:In this paper the evaporation of sessile water drops on soft viscoelastic substrates is investigated. We demonstrate how the deformation of the substrate close to the triple-phase Contact line influences the evaporation of a sessile drop by using surfaces with similar wettability, but different viscoelastic properties. We show that water drops on soft surfaces (Young's modulus ∼ 0.02 MPa) evaporate faster than those on hard surfaces (Young's modulus ∼ 1.5 MPa). The faster evaporation rates on soft surfaces can be related to a different dynamic evolution of the Receding Contact Angle, which is a direct consequence of the substrate deformation close to the triple-phase Contact line. By adjusting the substrate softness we are able to control the transition between constant Contact radius and constant Contact Angle evaporation modes.
Doris Vollmer - One of the best experts on this subject based on the ideXlab platform.
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direct observation of drops on slippery lubricant infused surfaces
Soft Matter, 2015Co-Authors: Frank Schellenberger, Periklis Papadopoulos, Alexandre Hardy, Hansjurgen Butt, Markus Klapper, Noemi Encinas, Doris VollmerAbstract:For a liquid droplet to slide down a solid planar surface, the surface usually has to be tilted above a critical Angle of approximately 10°. By contrast, droplets of nearly any liquid “slip” on lubricant-infused textured surfaces – so termed slippery surfaces – when tilted by only a few degrees. The mechanism of how the lubricant alters the static and dynamic properties of the drop remains elusive because the drop–lubricant interface is hidden. Here, we image the shape of drops on lubricant-infused surfaces by laser scanning confocal microscopy. The Contact Angle of the drop–lubricant interface with the substrate exceeds 140°, although macroscopic contour images suggest Angles as low as 60°. Confocal microscopy of moving drops reveals fundamentally different processes at the front and rear. Drops recede via discrete depinning events from surface protrusions at a defined Receding Contact Angle, whereas the advancing Contact Angle is 180°. Drops slide easily, as the apparent Contact Angles with the substrate are high and the drop–lubricant interfacial tension is typically lower than the drop–air interfacial tension. Slippery surfaces resemble superhydrophobic surfaces with two main differences: drops on a slippery surface are surrounded by a wetting ridge of adjustable height and the air underneath the drop in the case of a superhydrophobic surface is replaced by lubricant in the case of a slippery surface.
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characterization of super liquid repellent surfaces
Current Opinion in Colloid and Interface Science, 2014Co-Authors: Hansjuergen Butt, Periklis Papadopoulos, Doris Vollmer, Ilia V Roisman, Martin Brinkmann, Ciro SemprebonAbstract:Characterization of the wetting properties is a prerequisite for a fundamental understanding and the targeted development of superhydrophobic and superamphiphobic layers. To fabricate super liquid-repellent layers, two requirements need to be met: The surfaces have to be of low energy and their nano- and microstructure needs to be designed in a way that leads to the entrapment of air. The challenge is to design and produce suitable nano- and microstructures to control wetting. Here we describe important methods to quantify wetting properties of super liquid-repellent layers. These properties include the apparent advancing and Receding Contact Angles, the roll-off Angle, tensile and lateral adhesion, the impalement pressure, and the observation of drop impact. The most important one is the apparent Receding Contact Angle because it also limits lateral adhesion. The link of these properties to the nano- and microscopic structure of the layer is discussed. Limits, problems, and future challenges are pointed out.
