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Darsh T. Wasan - One of the best experts on this subject based on the ideXlab platform.
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Vertical Spreading of Aqueous Trisiloxane Solution Driven by a Spontaneously Developing Surface Tension Gradient
Industrial & Engineering Chemistry Research, 2008Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:This article reports the results of experiments conducted on the spontaneous climbing of an aqueous film of trisiloxane surfactants (“superspreaders”) on a vertical strongly hydrophobic solid Surface. The final height achieved is much in excess of that expected purely on the basis of the capillary wetting action and suggests that a spontaneously developing Surface Tension Gradient aids in film climbing. Maxima are observed in both the spreading rate and the height achieved as a function of the surfactant concentration, similar to the spreading of a superspreader drop on a horizontal hydrophobic Surface.
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Spreading of a Water Drop Triggered by the Surface Tension Gradient Created by the Localized Addition of a Surfactant
Industrial & Engineering Chemistry Research, 2007Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:The spreading of aqueous solutions of trisiloxane surfactants on solid Surfaces has been studied extensively. Trisiloxane surfactants are used in pesticide delivery as adjuvants to promote spreading on leaves and provide a larger area for solute transfer. The spreading of a dew-drop on a leaf when a spray of pesticide is delivered is simulated by studying the spreading of a water drop on a hydrophobic Surface when a small drop of aqueous trisiloxane surfactant is brought in contact with it. This study reveals many new features that differ from the spreading of an aqueous trisiloxane drop on a solid Surface; the spreading of the substrate drop is characterized by an inertial rather than a viscous response, the imposed Surface Tension Gradient dies out rapidly, and the spreading velocity is consistent with a balance of kinetic energy imparted to the substrate drop and the decrease in its Surface energy.
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Surface Tension Gradient driven spreading of trisiloxane surfactant solution on hydrophobic solid
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:Abstract The spreading of aqueous solutions of trisiloxane surfactant on hydrophobic Surfaces has been studied extensively, but the underlying mechanisms are still being debated. Recently, we advanced the view that the initial high rate of spreading is driven by the Surface Tension Gradient that develops spontaneously over the air–solution Surface due to surfactant depletion caused by stretching of this Surface. In this short paper, we substantiate this view with additional experiments. To understand the role of capillary forces, spreading experiments were conducted so that during the spreading of surfactant solution over the solid Surface, the fluid displaced from the solid was an organic liquid instead of air as is the usual case. Through this scheme, the balance of forces at the three phase contact line was altered, while retaining the same Surface Tension Gradient over the air–solution interface. Such experiments were also conducted on solid Surfaces of different wettability, to examine the role of the solid–liquid interfacial Tension on spreading rate. Our finding is that the initial rate of spreading is not influenced by the forces at the contact line or at the solid–solution interface, leading to the conclusion that the major driving force for spreading of trisiloxane surfactant solution on hydrophobic Surfaces is the Surface Tension Gradient over the air–solution Surface. The occurrence of a maximum in spreading area with surfactant concentration is shown to be consistent with this mechanism. We also present a comparison between a simplified theoretical model and experiments to support the conclusion of Surface Tension Gradient driven spreading.
Anoop Chengara - One of the best experts on this subject based on the ideXlab platform.
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Vertical Spreading of Aqueous Trisiloxane Solution Driven by a Spontaneously Developing Surface Tension Gradient
Industrial & Engineering Chemistry Research, 2008Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:This article reports the results of experiments conducted on the spontaneous climbing of an aqueous film of trisiloxane surfactants (“superspreaders”) on a vertical strongly hydrophobic solid Surface. The final height achieved is much in excess of that expected purely on the basis of the capillary wetting action and suggests that a spontaneously developing Surface Tension Gradient aids in film climbing. Maxima are observed in both the spreading rate and the height achieved as a function of the surfactant concentration, similar to the spreading of a superspreader drop on a horizontal hydrophobic Surface.
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Spreading of a Water Drop Triggered by the Surface Tension Gradient Created by the Localized Addition of a Surfactant
Industrial & Engineering Chemistry Research, 2007Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:The spreading of aqueous solutions of trisiloxane surfactants on solid Surfaces has been studied extensively. Trisiloxane surfactants are used in pesticide delivery as adjuvants to promote spreading on leaves and provide a larger area for solute transfer. The spreading of a dew-drop on a leaf when a spray of pesticide is delivered is simulated by studying the spreading of a water drop on a hydrophobic Surface when a small drop of aqueous trisiloxane surfactant is brought in contact with it. This study reveals many new features that differ from the spreading of an aqueous trisiloxane drop on a solid Surface; the spreading of the substrate drop is characterized by an inertial rather than a viscous response, the imposed Surface Tension Gradient dies out rapidly, and the spreading velocity is consistent with a balance of kinetic energy imparted to the substrate drop and the decrease in its Surface energy.
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Surface Tension Gradient driven spreading of trisiloxane surfactant solution on hydrophobic solid
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:Abstract The spreading of aqueous solutions of trisiloxane surfactant on hydrophobic Surfaces has been studied extensively, but the underlying mechanisms are still being debated. Recently, we advanced the view that the initial high rate of spreading is driven by the Surface Tension Gradient that develops spontaneously over the air–solution Surface due to surfactant depletion caused by stretching of this Surface. In this short paper, we substantiate this view with additional experiments. To understand the role of capillary forces, spreading experiments were conducted so that during the spreading of surfactant solution over the solid Surface, the fluid displaced from the solid was an organic liquid instead of air as is the usual case. Through this scheme, the balance of forces at the three phase contact line was altered, while retaining the same Surface Tension Gradient over the air–solution interface. Such experiments were also conducted on solid Surfaces of different wettability, to examine the role of the solid–liquid interfacial Tension on spreading rate. Our finding is that the initial rate of spreading is not influenced by the forces at the contact line or at the solid–solution interface, leading to the conclusion that the major driving force for spreading of trisiloxane surfactant solution on hydrophobic Surfaces is the Surface Tension Gradient over the air–solution Surface. The occurrence of a maximum in spreading area with surfactant concentration is shown to be consistent with this mechanism. We also present a comparison between a simplified theoretical model and experiments to support the conclusion of Surface Tension Gradient driven spreading.
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superspreading driven by marangoni flow
Advances in Colloid and Interface Science, 2002Co-Authors: Alex Nikolov, Anoop Chengara, D T Wasan, Kalman Koczo, George A Policello, Istvan KolossvaryAbstract:The spontaneous spreading (called superspreading) of aqueous trisiloxane ethoxylate surfactant solutions on hydrophobic solid Surfaces is a fascinating phenomenon with several practical applications. For example, the ability of trisiloxane ethoxylate surfactants to enhance the spreading of spray solutions on waxy weed leaf Surfaces, such as velvetleaf (Abutilion theophrasti), makes them excellent wetting agents for herbicide applications. The superspreading ability of silicone surfactants has been known for decades, but its mechanism is still not well understood. In this paper, we suggest that the spreading of trisiloxane ethoxylates is controlled by a Surface Tension Gradient, which forms when a drop of surfactant solution is placed on a solid Surface. The proposed model suggests that, as the spreading front stretches, the Surface Tension increases (the surfactant concentration becomes lower) at the front relative to the top of the droplet, thereby establishing a dynamic Surface Tension Gradient. The driving force for spreading is due to the Marangoni effect, and our experiments showed that the higher the Gradient, the faster the spreading. A simple model describing the phenomenon of superspreading is presented. We also suggest that the superspreading behavior of trisiloxane ethoxylates is a consequence of the molecular configuration at the air/water Surface (i.e. small and compact hydrophobic part), as shown by molecular dynamics modeling. We also found that the aggregates and vesicles formed in trisiloxane solutions do not initiate the spreading process and therefore these structures are not a requirement for the superspreading process.
Alex Nikolov - One of the best experts on this subject based on the ideXlab platform.
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Vertical Spreading of Aqueous Trisiloxane Solution Driven by a Spontaneously Developing Surface Tension Gradient
Industrial & Engineering Chemistry Research, 2008Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:This article reports the results of experiments conducted on the spontaneous climbing of an aqueous film of trisiloxane surfactants (“superspreaders”) on a vertical strongly hydrophobic solid Surface. The final height achieved is much in excess of that expected purely on the basis of the capillary wetting action and suggests that a spontaneously developing Surface Tension Gradient aids in film climbing. Maxima are observed in both the spreading rate and the height achieved as a function of the surfactant concentration, similar to the spreading of a superspreader drop on a horizontal hydrophobic Surface.
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Spreading of a Water Drop Triggered by the Surface Tension Gradient Created by the Localized Addition of a Surfactant
Industrial & Engineering Chemistry Research, 2007Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:The spreading of aqueous solutions of trisiloxane surfactants on solid Surfaces has been studied extensively. Trisiloxane surfactants are used in pesticide delivery as adjuvants to promote spreading on leaves and provide a larger area for solute transfer. The spreading of a dew-drop on a leaf when a spray of pesticide is delivered is simulated by studying the spreading of a water drop on a hydrophobic Surface when a small drop of aqueous trisiloxane surfactant is brought in contact with it. This study reveals many new features that differ from the spreading of an aqueous trisiloxane drop on a solid Surface; the spreading of the substrate drop is characterized by an inertial rather than a viscous response, the imposed Surface Tension Gradient dies out rapidly, and the spreading velocity is consistent with a balance of kinetic energy imparted to the substrate drop and the decrease in its Surface energy.
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Surface Tension Gradient driven spreading of trisiloxane surfactant solution on hydrophobic solid
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002Co-Authors: Anoop Chengara, Alex Nikolov, Darsh T. WasanAbstract:Abstract The spreading of aqueous solutions of trisiloxane surfactant on hydrophobic Surfaces has been studied extensively, but the underlying mechanisms are still being debated. Recently, we advanced the view that the initial high rate of spreading is driven by the Surface Tension Gradient that develops spontaneously over the air–solution Surface due to surfactant depletion caused by stretching of this Surface. In this short paper, we substantiate this view with additional experiments. To understand the role of capillary forces, spreading experiments were conducted so that during the spreading of surfactant solution over the solid Surface, the fluid displaced from the solid was an organic liquid instead of air as is the usual case. Through this scheme, the balance of forces at the three phase contact line was altered, while retaining the same Surface Tension Gradient over the air–solution interface. Such experiments were also conducted on solid Surfaces of different wettability, to examine the role of the solid–liquid interfacial Tension on spreading rate. Our finding is that the initial rate of spreading is not influenced by the forces at the contact line or at the solid–solution interface, leading to the conclusion that the major driving force for spreading of trisiloxane surfactant solution on hydrophobic Surfaces is the Surface Tension Gradient over the air–solution Surface. The occurrence of a maximum in spreading area with surfactant concentration is shown to be consistent with this mechanism. We also present a comparison between a simplified theoretical model and experiments to support the conclusion of Surface Tension Gradient driven spreading.
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superspreading driven by marangoni flow
Advances in Colloid and Interface Science, 2002Co-Authors: Alex Nikolov, Anoop Chengara, D T Wasan, Kalman Koczo, George A Policello, Istvan KolossvaryAbstract:The spontaneous spreading (called superspreading) of aqueous trisiloxane ethoxylate surfactant solutions on hydrophobic solid Surfaces is a fascinating phenomenon with several practical applications. For example, the ability of trisiloxane ethoxylate surfactants to enhance the spreading of spray solutions on waxy weed leaf Surfaces, such as velvetleaf (Abutilion theophrasti), makes them excellent wetting agents for herbicide applications. The superspreading ability of silicone surfactants has been known for decades, but its mechanism is still not well understood. In this paper, we suggest that the spreading of trisiloxane ethoxylates is controlled by a Surface Tension Gradient, which forms when a drop of surfactant solution is placed on a solid Surface. The proposed model suggests that, as the spreading front stretches, the Surface Tension increases (the surfactant concentration becomes lower) at the front relative to the top of the droplet, thereby establishing a dynamic Surface Tension Gradient. The driving force for spreading is due to the Marangoni effect, and our experiments showed that the higher the Gradient, the faster the spreading. A simple model describing the phenomenon of superspreading is presented. We also suggest that the superspreading behavior of trisiloxane ethoxylates is a consequence of the molecular configuration at the air/water Surface (i.e. small and compact hydrophobic part), as shown by molecular dynamics modeling. We also found that the aggregates and vesicles formed in trisiloxane solutions do not initiate the spreading process and therefore these structures are not a requirement for the superspreading process.
Anne-marie Cazabat - One of the best experts on this subject based on the ideXlab platform.
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The Thickness of Surface-Tension-Gradient-Driven Spreading Films
Journal of Colloid and Interface Science, 1993Co-Authors: Philippe Carles, Anne-marie CazabatAbstract:We present here a new interpretation of the origin of the thickness of Surface-Tension-Gradient-driven spreading films. Besides the already known regime, where this thickness is controlled by the influence of gravity and is proportional to the Surface Tension Gradient, we show the existence of another regime, where the curvature of the meniscus, out of which the film climbs, must be taken into account, and the thickness is proportional to the square of the Surface Tension Gradient. This situation corresponds to low Surface Tension Gradients, or equivalently to highly curved menisci. This theory is successfully used to explain the differences observed between two previously published papers (Ludviksson and Lightfoot, AIChE J. 17, 1166 (1971); Cazabat et al., Nature 346, 824 (1990)), and its predictions are checked by new experiments.
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The spreading of films by Surface Tension Gradients
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1993Co-Authors: Philippe Carles, Anne-marie Cazabat, E. KolbAbstract:Abstract We present theoretical and experimental investigations of thermally driven spreading films. As well as the already established regime, in which the thickness of the films is controlled by the influence of gravity and is proportional to the Surface Tension Gradient, another regime can be obtained in which the curvature of the meniscus (out of which the film climbs) must be taken into account. Here the thickness is proportional to the square of the Surface Tension Gradient. A systematic study of this regime has been performed for a “free meniscus”, the curvature of which is controlled by the capillary length, and low Gradients (see P. Carles, Doctoral Thesis, Paris, 1992). In this paper, we report preliminary investigations of highly curved menisci and larger Gradients. New processes have to be taken into account, i.e. the change in the shape of the meniscus at high Gradient and the presence of a precursor film on top of the main film at high curvatures, where this main film is especially thin and evolves slowly with time.
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On the Origin of the Bump in the Profile of Surface-Tension-Gradient-Driven Spreading Films
MRS Proceedings, 1991Co-Authors: Philippe Carles, Anne-marie CazabatAbstract:We show that the presence of a bump, in the profile of spreading films driven by forces such as Surface Tension Gradients, can be explained by a simple analysis of the steady-state velocity, without taking into account contact line effects.
Hiromitsu Kozuka - One of the best experts on this subject based on the ideXlab platform.
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spontaneous pattern formation induced by benard marangoni convection for sol gel derived titania dip coating films effect of co solvents with a high Surface Tension and low volatility
Langmuir, 2015Co-Authors: Hiroaki Uchiyama, Tadayuki Matsui, Hiromitsu KozukaAbstract:Evaporation-driven Surface Tension Gradient in the liquid layer often causes the convective flow, i.e., Benard–Marangoni convection, resulting in the formation of cell-like patterns on the Surface. Here, we prepared sol–gel-derived titania films from Ti(OC3H7i)4 solutions by dip coating and discussed the effect of the addition of co-solvents with a high Surface Tension and low volatility on the spontaneous pattern formation induced by Benard–Marangoni convection. Propylene glycol (PG, with a Surface Tension of 38.6 mN m–1) and dipropylene glycol (DPG, with a Surface Tension of 33.9 mN m–1) were added to the coating solutions containing 2-propanol (2-Pr, with a Surface Tension of 22.9 mN m–1) for controlling the evaporation-driven Surface Tension Gradient in the coating layer on a substrate. During dip coating at a substrate withdrawal speed of 50 cm min–1 in a thermostatic oven at 60 °C, linearly arranged cell-like patterns on a micrometer scale were spontaneously formed on the titania gel films, irrespec...
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spontaneous pattern formation induced by benard marangoni convection for sol gel derived titania dip coating films effect of co solvents with a high Surface Tension and low volatility
Langmuir, 2015Co-Authors: Hiroaki Uchiyama, Tadayuki Matsui, Hiromitsu KozukaAbstract:Evaporation-driven Surface Tension Gradient in the liquid layer often causes the convective flow, i.e., Benard-Marangoni convection, resulting in the formation of cell-like patterns on the Surface. Here, we prepared sol-gel-derived titania films from Ti(OC3H7(i))4 solutions by dip coating and discussed the effect of the addition of co-solvents with a high Surface Tension and low volatility on the spontaneous pattern formation induced by Benard-Marangoni convection. Propylene glycol (PG, with a Surface Tension of 38.6 mN m(-1)) and dipropylene glycol (DPG, with a Surface Tension of 33.9 mN m(-1)) were added to the coating solutions containing 2-propanol (2-Pr, with a Surface Tension of 22.9 mN m(-1)) for controlling the evaporation-driven Surface Tension Gradient in the coating layer on a substrate. During dip coating at a substrate withdrawal speed of 50 cm min(-1) in a thermostatic oven at 60 °C, linearly arranged cell-like patterns on a micrometer scale were spontaneously formed on the titania gel films, irrespective of the composition of coating solutions. Such Surface patterns remained even after the heat treatment at 200 and 600 °C, where the densification and crystallization of the titania films progressed. The width and height of the cell-like patterns increased with increasing PG and DPG contents in the coating solutions, where the addition of PG resulted in the formation of cells with a larger height than DPG.