Generation and Observation of Long-Lasting and Self-Sustaining Marangoni Flow

Abstract

When solute molecules in a liquid evaporate at the surface, concentration gradients can lead to surface tension gradients and provoke fluid convection at the interface, a phenomenon commonly known as the Marangoni effect. Here, we demonstrate that minute quantities of ethanol in concentrated sodium hydroxide solution can induce pronounced and long-lasting Marangoni flow upon evaporation at room temperature. By employing particle image velocimetry and gravimetric analysis, we show that the mean interfacial speed of the evaporating solution sensitively increases with the evaporation rate for ethanol concentrations lower than 0.5 mol %. Placing impermeable objects near the liquid−gas interface enforces steady concentration gradients, thereby promoting the formation of stationary flows. This allows for contact-free control of the flow pattern as well as its modification by altering the objects shape. Analysis of bulk flows reveals that the energy of evaporation in the case of stationary flows is converted to kinetic fluid energy with high efficiency, but reducing the sodium hydroxide concentration drastically suppresses the observed effect to the point where flows become entirely absent. Investigating the properties of concentrated sodium hydroxide solution suggests that ethanol dissolution in the bulk is strongly limited. At the surface, however, the co-solvent is efficiently stored, enabling rapid adsorption or desorption of the alcohol depending on its concentration in the adjacent gas phase. This facilitates the generation of large surface tension gradients and, in combination with the perpetual replenishment of the surface ethanol concentration by bulk convection, to the generation of longlasting, self-sustaining flows.

Experimental and theoretical research on oscillation behavior of droplets on horizontally oscillating substrates

“…In fact, using a video microscope, we observed that the carbon particles in the aqueous ethanol solution droplet moved sufficiently fast against the measurement interval, which is a phenomenon commonly known as Marangoni flow. 37,38) The developed method can obtain the physical properties of a droplet with high time resolution and capture unsteady phenomena, as shown in Fig. 7.…”

The Dynamics of Per- and Polyfluoroalkyl Substances (PFAS) at Interfaces in Porous Media: A Computational Roadmap from Nanoscale Molecular Dynamics Simulation to Macroscale Modeling

“…For verification of these models, the Marangoni number ( Ma - a dimensionless number that characterizes the Marangoni effect) can be used M a = Δ σ L m μ D Here, Δσ is the change in the interfacial tension [MT –2 ] (due to a solute concentration) along the characteristic length L m ; μ is the dynamic viscosity [ML –1 T –1 ]; and D is the diffusion coefficient [L 2 T –1 ] . The Marangoni number concept is applicable to studies across scales ,− and thus adaptable to quantitative studies of the PFAS interaction in multiphase systems for the development of transport model systems.…”

Speleothem-Inspired Copper/Nickel Interfaces for Enhanced Liquid–Vapor Transport by Marangoni and Soret Effects

“…The Soret effect, or thermal diffusion, causes a separation of the mixture components in response to a temperature gradient. , The Marangoni effect, on the other hand, induces fluid motion along the interface due to a surface tension gradient. This effect can cause the vapor bubbles in the binary mixture to shift toward the high-temperature area, further promoting liquid replenishment at the nucleation sites and preventing dry-out. , The impact of the Soret and Marangoni effects on heat transfer characteristics has been well-documented for plain surfaces. However, there is a lack of theoretical frameworks and empirical correlations that account for the influence of heater surface attributes on these complex phenomena.…”