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Applications of surfactants in paints
Published in David R. Karsa, Surfactants in Polymers, Coatings, Inks and Adhesives, 2020
The acetylenediols mentioned above are popular in coating formulations as low-foaming or defoaming surfactants. It has been claimed that the special geometry of these surfactants favours foam destabilization [30]. A conventional surfactant, such as an alcohol ethoxylate or an alkylphenol ethoxylate, forms a well ordered monolayer at the air/water interface. If the liquid lamella is stretched, there will be less surfactant in the stretched segment, i.e. the surface tension in this segment will be high. The so-called Gibbs-Marangoni effect will cause a transport of surfactant along the surface in order to restore the low surface tension. In this transport the surfactant will pull water along, thus restoring also the width of the lamella (Figure 6.11). In order for this restoring mechanism to be effective, the surfactant must have a relatively low bulk concentration, i.e. the critical micelle concentration must be relatively low [26]. Acetylenediols do not align well at interfaces. Instead, they are believed to be horizontally adsorbed at the air/water interface. If a foam film is disturbed, leading to regions of high surface tension, this type of surfactant will be transported to the area of high surface tension by bulk diffusion, not by lateral movement at the surface. The low surface tension will eventually be restored but, since water will not be pulled along the surface, the stretched part of the lamella will remain thin and fragile.
Wetting of Wetting/Spreading in the Presence of Surfactants
Published in Victor M. Starov, Manuel G. Velarde, Wetting and Spreading Dynamics, 2019
Victor M. Starov, Manuel G. Velarde
where η and u are the liquid dynamic shear viscosity and tangential velocity on the liquid surface located at height h, respectively; (r, z) are radial and vertical coordinates; and γ(Γ) is the liquid–air interfacial tension whose linear dependency on surfactant surface concentration we assume below in this section. The surface tension gradient-driven flow induced by the Marangoni effect moves surfactant along the surface, and a dramatic spreading process takes place. Then the liquid–air interface deviates from an initially flat position to accommodate with the normal stress also occurring during motion.
2 Capture Based on Chemical Absorption
Published in I. M. Mujtaba, R. Srinivasan, N. O. Elbashir, The Water–Food–Energy Nexus, 2017
Atuman S. Joel, Eni Oko, Meihong Wang, Colin Ramshaw, Jonathan G. M. Lee, KeJun Wu, DoYeon Kim, Nilay Shah, Lin Ma, Mohamed Pourkashanian
The Marangoni effect occurs when there is a gradient of surface tension at the interface between two phases. In most cases, this is a gas–liquid interface. The surface tension typically changes due to variations in solute concentration, surfactant concentration, and temperature variations along the interface.
A review on control of droplet motion based on wettability modulation: principles, design strategies, recent progress, and applications
Published in Science and Technology of Advanced Materials, 2022
Mizuki Tenjimbayashi, Kengo Manabe
First, we summarize the significant findings from the perspective of phenomenon and theory. In 1756, the Leidenfrost phenomenon was discovered in which droplets levitate on a superheated substrate [4]. In 1787, Monge reported that capillary action was an outcome of the superficial nature of the liquid [5]. Young presented a quantitative study of wetting phenomena in 1805 [6]. In his essay, he quantified the wettability of a droplet in terms of the contact angle. He showed that the contact angle is determined by the cohesive force of the droplet and the interfacial interaction (interfacial tension or capillary force) with the contacting substrate. The phenomenon wherein a gradient in the capillary force becomes the driving force for mass transfer between fluids is called the Marangoni effect. This effect was recognized by Thomson and Belfast in the ‘tears of wine’ phenomenon in 1855 [2] and studied by Marangoni in 1865 [7]. In 1878, Gibbs identified a frictional resistance in the movement of droplet contact lines [8]. Wenzel proposed models for droplet wetting behavior on rough surfaces in 1936 [9], followed by Cassie and Baxter in 1944 [10]. In 1964, Johnson and Dettre reported the relationship between droplet adhesion behavior (contact angle hysteresis) and surface roughness [11]. These studies laid the foundation for the classical theory of wetting. They suggested that surface chemical composition and structure are crucial in controlling wettability.
Pore-scale visual investigation on the spontaneous imbibition of surfactant solution in oil-wet capillary tubes
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Bingbing Li, Weiyao Zhu, Qipeng Ma, Hua Li, Debin Kong, Zhiyong Song
Due to the surfactant continuously diffused at the oil–water interface, the distribution of surfactant concentration at the interface was an imbalance, which resulted in the appearance of tension gradient on both sides of the oil–water interface, namely the Marangoni effect (Zhao et al. 2020a). The concentration of surfactant at the interface surpassed that of the oil phase, which induced the oil moved toward the direction of surfactant to counteract the concentration difference (Mirzaei, DiCarlo, and Pope 2016). Additionally, the negative charge released from silica repelled the negative charge of surfactant molecules, which lead to the concentration in the middle was higher than the concentration on the boundary. That was one of the main reasons for the distribution characteristics of the velocity field in Section 3.2. Wettability alteration might be conducive to reduce the capillary force on the side of the surfactant, and IFT reduction would also lead to the decrease of capillary force, whereas the capillary force on the side of the oil phase appeared to be constant. The imbibition distance of the surfactant solution in the capillary tube was prolonged by these two potential macroscopic factors. In brief, surfactant molecules could get into the oil phase through diffusion effect, and the induced Marangoni effect promoted the surfactant molecules to continue to diffuse in the capillary tube. When the resistance composed of capillary force and viscous force neutralized the motive power, the recovery of spontaneous imbibition in the capillary tube was balanced (Morrow and Mason 2001).
A homogenization approach to the effect of surfactant concentration and interfacial slip on the flow past viscous drops
Published in Applicable Analysis, 2023
H. S. Mahato, G. P. Raja Sekhar
While these works are mostly on the migration of viscous drop in pure ambient viscous flows, there are also studies concerned with the effect of surfactants on the motion of drops and droplets in creeping flow. Surfactants are surface active agents that are adsorbed at a fluid–fluid interface or at a fluid–gas interface [3,4,16–19]. The surfactants usually lower the interfacial tension and cause a Marangoni effect. It is observed that even a small amount of surfactant can reduce the terminal velocity of a drop [20], where the authors have studied the effect of surfactants on the terminal velocity of a drop in an axisymmetric flow. Along the interface, the surfactant is governed by a convection–diffusion equation [18,21,22], where the authors have formulated a problem in the context of concrete carbonation in a micro–macro scale setting. The authors in [23,24] have used the collocation method to solve the convection–diffusion problem for high Péclet numbers and studied the retardation of drop motion when the surfactant is present. The authors in [25] studied the flow past a drop which is partially coated with a stagnant layer of surfactant for large surface Péclet number. Several works have been done where the effects of soluble and insoluble surfactants on the motion of drops using various numerical techniques are considered [26,27]. It should be noted that the existing literature dealing with thermocapillary migration of drops contributed explicit idea or numerical treatment. Similarly, the collective behavior of the drops has been investigated via experimental means or simulations. These were though no attempts dealing with rich mathematical theory applied to understand the collective behavior of surfactant coated drops.