Physicochemical hydrodynamics of droplets out of equilibrium

Abstract

Droplets abound in nature and technology. In general, they are multicomponent, and, when out of equilibrium, with gradients in concentration, implying flow and mass transport. Moreover, phase transitions can occur, with either evaporation, solidification, dissolution, or nucleation of a new phase. The droplets and their surrounding liquid can be binary, ternary, or contain even more components, and with several even in different phases. In the last two decades the rapid advances in experimental and numerical fluid dynamical techniques has enabled major progress in our understanding of the physicochemical hydrodynamics of such droplets, further narrowing the gap from fluid dynamics to chemical engineering and colloid & interfacial science and arriving at a quantitative understanding of multicomponent and multiphase droplet systems far from equilibrium, and aiming towards a one-to-one comparison between experiments and theory or numerics. This review will discuss various examples of the physicochemical hydrodynamics of droplet systems far from equilibrium and our present understanding of them. These include immiscible droplets in a concentration gradient, coalescence of droplets of different liquids, droplets in concentration gradients emerging from chemical reactions (including droplets as microswimmers) and phase transitions such as evaporation, solidification, dissolution, or nucleation, and droplets in ternary liquids, including solvent exchange, nano-precipitation, and the so-called ouzo effect. We will also discuss the relevance of the physicochemical hydrodynamics of such droplet systems for many important applications, including in chemical analysis and diagnostics, microanalysis, pharmaceutics, synthetic chemistry and biology, chemical and environmental engineering, the oil and remediation industries, inkjet-printing, for micro-and nano-materials, and in nanotechnolgoy.

Two-layer thermally driven turbulence: mechanisms for interface breakup

“…Clearly, buoyancy will also play a prominent role in the interfacial breakup in other turbulent flows, such as Bénard-Marangoni convection, and horizontal and vertical convection. All these phenomena add to the richness of physico-chemical hydrodynamics of droplets far from equilibrium (Lohse & Zhang 2020).…”

Dynamics of hygroscopic aqueous solution droplets undergoing evaporation or vapour absorption

“…In recent years, studies on multicomponent droplets have revealed attractive physical phenomena (Lohse & Zhang 2020) induced by the preferential evaporation of individual components or mediated by external vapour sources, e.g. the occurrence of density-driven flows (Edwards et al 2018;Li et al 2019), phase segregation/separation (Li et al 2018;Li et al 2020;Mao et al 2020), the transient Marangoni flow and solutal effects (Christy, Hamamoto & Sefiane 2011), etc.…”

Universality in microdroplet nucleation during solvent exchange in Hele-Shaw-like channels

“…This limitation can be overcome in a bottom-up approach such as solvent exchange (Lou et al 2000;, 2020Zhang et al 2015), where a large number of micro-and nanodroplets are generated by nucleation out of an oversaturated solution. This method, also called nanoprecipitation or solvent shifting (Fessi et al 1989;Galindo-Rodriguez et al 2004;Aubry et al 2009;Lepeltier, Bourgaux & Couvreur 2014;Hajian & Hardt 2015), though commonly used, is much less well understood.…”