Further Step toward a Comprehensive Understanding of the Effect of Surfactant Additions on Altering the Impact Dynamics of Water Droplets

Abstract

The addition of surfactants to pure water for specific applications has made controlling the impact dynamics of surfactant-laden droplets a complex phenomenon. This work investigates the influence of the molecular weight (MW), concentration, and ionic nature of the surfactants as well as the substrate surface characteristics on the impact dynamics of surfactant-laden droplets using a high-speed camera at 10 000 frames per second. Sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and n-decanoyl-n-methylglucamine were used as anionic, cationic, and nonionic surfactants, respectively. We used hydrophilic glass slides, hydrophobic polytetrafluoroethylene, and superhydrophobic alkyl ketene dimer (AKD) as substrates. The results show that the efficiency of the surfactant addition in increasing the maximum spreading diameter is significantly influenced by the molecular weight and ionic nature of the solutions as well as the nonwettability of the substrate. Among all of the surfaces examined, the concentration and ionic nature of the solutions were found to be more dominant parameters in determining the energy dissipation in the retraction phase of the droplet impact on the superhydrophobic AKD surfaces. As the concentration decreases or positive charges are present in the solution, it is more likely to observe a similar retraction dynamic to pure water when the droplet hits the superhydrophobic AKD having negatively charged surface sites. Finally, in terms of the impact outcomes of the surfactant-laden droplets on the superhydrophobic AKD, it is shown that the influence of the surfactant addition is more noticeable at lower Weber numbers, where the droplet tries to rebound by overcoming the energy loss that occurred in the spreading.

Impact Dynamics and Freezing Behavior of Surfactant-Laden Droplets on Non-Wettable Coatings at Subzero Temperatures

“…At this point, by increasing the concentration of the solutions further to 2 × CMC, no notable change is observed in the surface tension values, which is in agreement with the previous studies on these solutions. 25,36 This phenomenon is interpreted as the formation of micellar bilayers on the surface, which prohibits any further changes in the surface tension of the solutions with the increase in the concentration. 37,38 Based on the data of Figure 2, we divided the solutions into three groups with each having an almost similar equilibrium surface tension to separately study the influence of molecular weight and ionic nature of the surfactants on the droplet dynamics at subzero temperatures.…”

“…More details regarding surface characterization of the samples used in the current work, including the surface free energy, roughness, and morphology, can be found in our recent comprehensive studies on non-wettable AKD coatings. 25,34,35 According to roughness characterization of the fabricated samples, the root mean square (RMS) value of the substrates is approximately 2.92 μm. 25 To study the influence of concentration, molecular weight, and ionic nature of surfactants on the impact dynamics and freezing behavior of the solutions, three well-known surfactants, sodium dodecyl sulfate (SDS, anionic), hexadecyltrimethylammonium bromide (CTAB, cationic), and n-decanoyl-n-methylglucamine (MEGA-10, nonionic) were used (Sigma-Aldrich, USA).…”

“…25,34,35 According to roughness characterization of the fabricated samples, the root mean square (RMS) value of the substrates is approximately 2.92 μm. 25 To study the influence of concentration, molecular weight, and ionic nature of surfactants on the impact dynamics and freezing behavior of the solutions, three well-known surfactants, sodium dodecyl sulfate (SDS, anionic), hexadecyltrimethylammonium bromide (CTAB, cationic), and n-decanoyl-n-methylglucamine (MEGA-10, nonionic) were used (Sigma-Aldrich, USA). To prepare the solutions, a specific amount of each surfactant was dissolved in deionized water at room temperature to reach the desired concentration.…”

Impact Dynamics of Nanodroplets on V-Shaped Substrates: Asymmetrical Behavior and Fast-Rebound Dynamics

“…The impact behavior of the drops on the solid substrate is a frequently studied phenomenon in fluid mechanics because of numerous industrial and daily applications ranging from spray coating, inkjet printing, , aeronautics, , to criminal forensics . During the impact process, there are two main stages, including spreading and retraction, and various outcomes of the drop, such as splash, deposition, and rebound, , which are highly determined by liquid properties (e.g., size, density, viscosity, surface tension), substrate properties (e.g., wettability, roughness, surface nano/microstructure, shape, elasticity, or porosity), and impact conditions (e.g., impact velocity, environment temperature and humidity, gas pressure, and so on). ,− Among these, the design of surface structures is the most commonly used method to tune the droplet dynamics . Generally speaking, the control of the drop impact dynamics for application has two aspects.…”

Droplet Impact on Surfaces with Asymmetric Microscopic Features

“… 5 , 6 The complex fluid–surface interaction during the impact—which includes splashing 7 − 11 and trapping of a thin gas film underneath the droplet 12 − 15 —has been studied theoretically, 16 − 19 numerically, 18 − 21 and experimentally. 22 − 28 These studies have established useful scaling laws of maximal deformation, which among other things are reviewed in ref ( 2 , 29 ).…”