Influence of evaporation on the morphology of a thin film of a partially miscible binary mixture

Abstract

In this paper, we develop numerical, theoretical and experimental analyses of the different morphologies that can be created by the phase separation phenomena that are induced by solvent evaporation in a thin film of a partially miscible binary mixture. Disregarding hydrodynamic effects, the Cahn-Hilliard-Cook and temperature equations are used to describe the thermodynamics of non-isothermal phase separation in a 2D thin film. Numerical simulations are performed to investigate the interplay between evaporation and phase separation and we examine the effect on the morphology of the film of several parameters such as the initial thickness of the layer, or the initial temperature and concentration of the mixture. Interestingly, the competition between evaporation and phase separation is shown to be the main determinant of the choice between a lamellar or a lateral pattern in the beginning of phase separation. For moderate evaporation rate, the spinodal instability takes place close to the evaporating interface and a lateral structure is formed. For stronger evaporation, the spinodal instability does not occur and a lamellar structure is created. In addition, the mid-or long-term evolution of the system is also considered. The thickness of the film is an important parameter in this analysis and possible modifications of the pattern over time are emphasized. Detailed physical and theoretical interpretations are proposed for the results and experiments in a Hele-Shaw cell that nicely confirm our predictions are presented.

A Mesoscopic Lattice Model for Morphology Formation in Ternary Mixtures with Evaporation

“…As first step, we will be investigating which of the geometric structures of the morphologies formed via our mesoscopic simulations can be via changing parameters in the Cahn-Hilliard-Cook model from [11] (or other variants as reported e.g. in [28,29,32], and, more recently, in [26]), and which are not obtainable via such macroscopic-level simulations.…”

“…On the other hand, with the current scaling we are unable to obtain mean-field effects. More work is needed in this direction, especially if one is tempted to find a rigorous link between the morphologies obtained with microscopic and/or mesoscopic lattice models, as done here, with the ones obtained by means of coupled systems of Cahn-Hilliard-type models, as for instance was performed in [26,30,32] and references cited therein.…”

State-of-the-art review of porous polymer membrane formation characterization—How numerical and experimental approaches dovetail to drive innovation

“…Because of the non-uniform temperature in the horizontal dimension and the decrease of the temperature with time, membrane structure with a spatial gradient in the pore size is obtained. TIPS via phase-field simulations has also been studied in Rogers (1989), Graham et al (1997), Barton and McHugh (1999), and Goyal et al (2021).…”

A Theoretical Perspective on the Thermodynamic Stability of Polymer Blends for Solar Cells: From Experiments to Predictive Modeling

“…[171] Finally, the morphology evolution of the full active layer can be simulated by continuum approaches, such as phase field (PF) models. [172][173][174][175] These are typically used to model the kinetics of phase separation of donor:acceptor blends by the Cahn-Hilliard equation, [176,177] which evaluates the change of local composition with annealing time. PF models require the knowledge of a number of effective parameters of the blend, including the Flory-Huggins parameters and donor/acceptor/solvent interface energies, which can be obtained from experiments or by atomistic/CG simulations as described earlier.…”