Physicochemical hydrodynamics in confined multicomponent liquids

Abstract

When a system contains more than one liquid, each liquid will evaporate depending on the volatility and the composition close to the evaporating interface. Based on Raoult's law [50] and the non-ideality of the mixture, the concentration of water-vapor close to the surface is modified aswhere a w is the thermodynamic activity of water, x w the mole fraction of water in the liquid, and ψ w (x w ) the activity coefficient of water corresponding to x w [51]. For an ideal mixture, a w = x w and ψ w = 1. Thus, for multicomponent liquids, the local evaporation rate changes with changes in the local composition. Therefore, to determine the evaporation rates in such systems, one can resort to numerical simulations to easily account for the spatio-temporal changes in composition and mixture properties [46]. However, in Chapters 2 and 5, we will show cases where we can still analytically determine the evaporation rates for multicomponent mixtures, albeit under simplifying assumptions, which will be complemented by corresponding direct numerical simulations. Evaporation-induced secondary processesSimilar to pure liquids, evaporation of multicomponent liquids can produce capillary flow, thermal Marangoni flow, and buoyancy-driven flow. However, in multicomponent liquids, the secondary processes also result from the spatiotemporal changes in the composition. Thus, evaporation in multicomponent liquids can trigger phenomenologically richer secondary processes compared to pure liquids. Such secondary processes include fluid flows [44,46,52], nontrivial contact line motion [53], segregation [49,54], and phase separation [48] (Figure 1.5). We discuss a few of these processes below: (a) Solutal Marangoni flow by selective evaporation Selective evaporation of the more volatile liquid in droplets and capillaries results in spatial gradients in concentration. Such spatial concentration gradients can lead to gradients in interfacial tension. Surface tension gradients lead to flows which are termed as solutal Marangoni flows [46, 52] (Figure 1.5 a), in contrast to the thermal Marangoni flows that are caused by temperature gradients. The direction of solutal Marangoni flow depends on whether 1.4. EVAPORATION OF MULTICOMPONENT LIQUIDS 13 14 CHAPTER 1. INTRODUCTION 1.5. EVAPORATION-INDUCED SELF-ASSEMBLY OF PARTICLES 15 1.5. EVAPORATION-INDUCED SELF-ASSEMBLY OF PARTICLES 17 18 CHAPTER 1. INTRODUCTION Chapter 4. System: Particles dispersed in an evaporating ternary ouzo droplet. Questions: Does modifying the surface properties of particles affect the supraparticles formed using self-lubricating ouzo droplets? If yes, which surface modifications have a stronger influence on the supraparticle formation? Chapter 5 System: Binary mixture of water and glycerol in thin capillaries. Questions: How is the evaporation of a binary mixture in a capillary different from that of a pure liquid? Can we analytically model the evaporation of binary liquid mixtures in a capillary? What are the important control parameters that determine the evaporation behav...