Instability and dynamics of volatile thin films

Abstract

Volatile viscous fluids on partially-wetting solid substrates can exhibit interesting interfacial instabilities and pattern formation. We study the dynamics of vapor condensation and fluid evaporation governed by a one-sided model in a low Reynolds number lubrication approximation incorporating surface tension, intermolecular effects and evaporative fluxes. Parameter ranges for evaporationdominated and condensation-dominated regimes and a critical case are identified. Interfacial instabilities driven by the competition between the disjoining pressure and evaporative effects are studied via linear stability analysis. Transient pattern formation in nearly-flat evolving films in the critical case is investigated. In the weak evaporation limit unstable modes of finite amplitude non-uniform steady states lead to rich droplet dynamics, including flattening, symmetry breaking, and droplet merging. Numerical simulations show long time behaviors leading to evaporation or condensation are sensitive to transitions between film-wise and drop-wise dynamics.

Sessile drop evaporation in a gap – crossover between diffusion-limited and phase transition-limited regime

“…The transition-limited case is considered in a number of different variants. The 'kinetic' approach by Burelbach, Bankoff & Davis (1988) and Joo, Davis & Bankoff (1991) assumes a uniform constant saturated vapour density in the gas and determines the strength of evaporation/condensation via the difference of film surface temperature and the uniform saturation temperature in the gas phase. The approach is also normally applied if evaporation is into a pure vapour atmosphere, i.e.…”

“…However, these effects are included in another variant of the transition-limited case, as presented by Potash & Wayner (1972), Moosman & Homsy (1980), Wayner (1993), Sharma (1998), Padmakar, Kargupta & Sharma (1999), Kargupta, Konnur & Sharma (2001), Ajaev & Homsy (2006) and Ji & Witelski (2018). It seems the earliest model for an evaporating meniscus influenced by Laplace (curvature) and Derjaguin (or disjoining) pressures is given by Potash & Wayner (1972), where evaporation into pure vapour is considered.…”

Sessile drop evaporation in a gap -- crossover between diffusion-limited and phase transition-limited regime

“…Although the involved processes can be modelled employing the full hydrodynamic description based on (Navier-)Stokes equations for the liquid and (advection-)diffusion equations for solutes in the liquid and vapour in the gas phase (Petsi & Burganos 2008;Bhardwaj et al 2009), in many cases reduced descriptions are used. Common examples are long-wave (or lubrication, or thin-film) models for the liquid that are valid for small contact angles and interface slopes (Oron et al 1997;Craster & Matar 2009;Saxton et al 2016;Ji & Witelski 2018).…”

“…However, these effects are included in another flavour of the transition-limited case as presented by Potash & Wayner (1972); Moosman & Homsy (1980); Wayner (1993); Sharma (1998); Padmakar et al (1999); Kargupta et al (2001); Ajaev & Homsy (2006); Ji & Witelski (2018). It seems the earliest model for an evaporating meniscus influenced by Laplace (curvature) and Derjaguin (or disjoining) pressures is given by Potash & Wayner (1972), where evaporation into pure vapour is considered.…”

Hierarchical Morphology of Polymer Blend Films Induced by Convection-Driven Solvent Evaporation

“…Phase separation plays a vital role in the controllable morphology, which dominates the performance of polymer blend films covering a wide range of fields such as optoelectronics, sensor, biomedicine, and so on. − Spin coating has been the prime choice as a film-forming method because of its easy-to-implement smoothing and accelerated drying of liquid films. − When combined with a mixture of solvents, the designed microphase separation has been pushed to a far-reaching refinement toward the optimization of device performance at the laboratory scale as in the field of optoelectronics. − In the rotating liquid film, however, the stimulated solvent evaporation removes the heat from the surface, leaving the inhomogeneous concentration and temperature fluctuations, both of which lead to the fluid flow and disturb the film morphology at the mesoscale. − Consequently, it remains challenging to obtain a mesoscale uniform film while retaining the desired microphase morphology, suggesting that heterogeneous deposition exists in the film formation under fluid disturbance, which goes beyond the traditional phase separation mechanism and arouses the urgent in-depth research for the coupling effect of fluid disturbance and phase separation. − …”