Thermodynamics of chemical Marangoni-driven engines

Abstract

The goal of this paper is to perform a general thermodynamic study of Marangoni-driven engines in which chemical energy is directly transformed into mechanical motion. Given that this topic has not been discussed before, we will explore here the most basic and fundamental aspects of the phenomena at work, which leads to a number of interesting observations typical of controversies in classical thermodynamics. Starting with a discussion of a few key motivating examples of chemical Marangoni-driven phenomena - tears of wine, an oscillating pendant droplet, "beating" oil lens, and traveling waves in a circular container - and contrasting homogeneous versus inhomogeneous thermodynamic systems we naturally arrive at alternative ways of storing and generating energy with the help of inhomogeneities in the bulk and surface properties of the working media. Of particular interest here are systems with interfaces - hence, in this context we discuss the nature and efficiency of the corresponding thermodynamic cycles leading to work done as a result of a non-uniform distribution of surface tension, which is in turn induced by a non-uniform surface active substance (surfactant) distribution, for both soluble and insoluble surfactants. Based on the relevant physical parameters of the working medium we can also evaluate the isothermality, i.e. temperature variations, dissipative losses, energy output and efficiency, entropy generation, and the period of such cycles in real processes. The role of singularity formation at the interface for the existence of such thermodynamic cycles is unraveled as well. Finally the discussion is concluded with a few ideas for potential applications of Marangoni-driven engines.

Superposition of Translational and Rotational Motions under Self-Propulsion of Liquid Marbles Filled with Aqueous Solutions of Camphor

“…Thus, the general model describing the self-propulsion is represented by eq . The Marangoni solutocapillary-induced motion − ,,,− can be described by the system of Newtonian equations as follows: where m and v⃗ cm are the mass and velocity of the center of mass of the marble, respectively (the change in the mass of marble due to evaporation is neglected) . The second term on the right-hand side in eq (namely, α a 2 ∇γ) is the Marangoni force .…”

“…Co-occurrence of soluto- and thermocapillary Marangoni flows is often observed under self-propulsion. , Thermal imaging of the self-propulsion of liquid marbles containing saturated aqueous solutions of camphor (see section ) showed that the temperature field formed at the liquid support surface under self-propulsion was not uniform, and the maximal change in temperature across the liquid/vapor interface was established as Δ T max ≅ 0.25 K.…”

“…Self-propulsion occurs under breaking of spherical symmetry of a nonstick droplet, taking place when evaporation of the volatile compound (camphor) in a certain direction is spontaneously increased . A volatile compound evaporated from a marble and consequently adsorbed at a water/vapor interface produces Marangoni solutocapillary flows, resulting in the self-propulsion of a droplet. − …”

Bio-inspired untethered fully soft robots in liquid actuated by induced energy gradients

“…‘Tears of wine’ was first observed in 1855 [ 28 ] and consequently recognized as an interfacial phenomenon of mass transport due to the surface-tension gradient [ 29 - 31 ] or, in brief, the Marangoni effect. The usage of a surface-tension gradient in propulsion by a few insects was discovered in succession [ 32 - 34 ] and then named as Marangoni propulsion consequently [ 35 , 36 ]. Among these insects are rove beetles in genus Stenus—a kind of beetle that generally lives around ponds and streams.…”

Evolution of entrained water film thickness and dynamics of Marangoni flow in Marangoni drying

“…Owing to the ability to drive and control fluid flow, 1 the Marangoni effect 2–5 has been applied in many technologies, including self-assembly, 6,7 coating, 8–10 and Marangoni drying. 11,12 Marangoni drying can realize the drying of wafers by Marangoni-driven flow after a sequence of wet cleaning processes, and it has been widely employed in the manufacturing of integrated circuits (ICs).…”