Marangoni effect

About: Marangoni effect is a research topic. Over the lifetime, 5336 publications have been published within this topic receiving 98562 citations. The topic is also known as: Gibbs–Marangoni effect.

Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study

Abstract: An efficient way to precisely pattern particles on solid surfaces is to dispense and evaporate colloidal drops, as for bioassays The dried deposits often exhibit complex structures exemplified by the coffee ring pattern, where most particles have accumulated at the periphery of the deposit In this work, the formation of deposits during the drying of nanoliter colloidal drops on a flat substrate is investigated numerically and experimentally A finite-element numerical model is developed that solves the Navier–Stokes, heat and mass transport equations in a Lagrangian framework The diffusion of vapor in the atmosphere is solved numerically, providing an exact boundary condition for the evaporative flux at the droplet–air interface Laplace stresses and thermal Marangoni stresses are accounted for The particle concentration is tracked by solving a continuum advection–diffusion equation Wetting line motion and the interaction of the free surface of the drop with the growing deposit are modeled based on criteria on wetting angles Numerical results for evaporation times and flow field are in very good agreement with published experimental and theoretical results We also performed transient visualization experiments of water and isopropanol drops loaded with polystyrene microspheres evaporating on glass and polydimethylsiloxane substrates, respectively Measured evaporation times, deposit shapes and sizes and flow fields are in very good agreement with the numerical results Different flow patterns caused by the competition of Marangoni loops and radial flow are shown to determine the deposit shape to be either a ring-like pattern or a homogeneous bump

Insoluble surfactant spreading on a thin viscous film: Shock evolution and film rupture

Abstract: Lubrication theory and similarity methods are used to determine the spreading rate of a localized monolayer of insoluble surfactant on the surface of a thin viscous film, in the limit of weak capillarity and weak surface diffusion. If the total mass of surfactant increases as t(alpha), then at early times, when spreading is driven predominantly by Marangoni forces, a planar (axisymmetric) region of surfactant is shown to spread as t(1 + alpha)/3 (t(1 + alpha)/4) . A shock exists at the leading edge of the monolayer; asymptotic methods are used to show that a wavetrain due to capillary forces exists ahead of the shock at small times, but that after a finite time it is swamped by diffusive effects. For alpha < 1/2 (alpha < 1), the diffusive lengthscale at the shock grows faster than the length of the monolayer, ultimately destroying the shock; subsequently, spreading is driven by diffusion, and proceeds as t1/2. The asymptotic results are shown to be good approximations of numerical solutions of the governing partial differential equations in the appropriate limits. Additional forces are also considered: weak vertical gravity can also destroy the shock in finite time, while effects usually neglected from lubrication theory are important only early in spreading. Experiments have shown that the severe thinning of the film behind the shock can cause it to rupture: the dryout process is modelled by introducing van der Waals forces.

Formation of Immiscible Alloy Powders with Egg-Type Microstructure

Abstract: The egg-type core microstructure where one alloy encases another has previously been obtained during experiments in space. Working with copper-iron base alloys prepared by conventional gas atomization, we were able to obtain this microstructure under gravity conditions. The minor liquid phase always formed the core of the egg, and it sometimes also formed a shell layer. The origin of the formation of this core microstructure can be explained by Marangoni motion on the basis of the temperature dependence of the interfacial energy, which shows that this type of powder can be formed even if the cooling rate is very high.