Modeling Solution Drying by Moving a Liquid-Vapor Interface: Method and Applications

Abstract

A method of simulating the drying process of a soft matter solution with an implicit solvent model by moving the liquid-vapor interface is applied to various solution films and droplets. For a solution of a polymer and nanoparticles, we observe “polymer-on-top” stratification, similar to that found previously with an explicit solvent model. Furthermore, “polymer-on-top” is found even when the nanoparticle size is smaller than the radius of gyration of the polymer chains. For a suspension droplet of a bidisperse mixture of nanoparticles, we show that core-shell clusters of nanoparticles can be obtained via the “small-on-outside” stratification mechanism at fast evaporation rates. “Large-on-outside” stratification and uniform particle distribution are also observed when the evaporation rate is reduced. Polymeric particles with various morphologies, including Janus spheres, core-shell particles, and patchy particles, are produced from drying droplets of polymer solutions by combining fast evaporation with a controlled interaction between the polymers and the liquid-vapor interface. Our results validate the applicability of the moving interface method to a wide range of drying systems. The limitations of the method are pointed out and cautions are provided to potential practitioners on cases where the method might fail.

Deposition Patterns Induced by the Evaporation of the Cyclic Diblock Copolymer Solution Droplet

“…40 Cheng et al studied the evaporation of the linear diblock copolymer solution droplet using the implicit solvent MD simulation combined with the moving interface method. 60 They further point out that the coffee-ring structure is hard to be observed without considering the flow inside the droplet. On the basis of the above discussion, internal flows inside the droplet always play an important role in the nonuniform distribution of polymers among the deposition pattern, such as the coffee-ring structure.…”

“…Kravchenko and Potemkin studied the deposition pattern of the linear homopolymer solution in a droplet . Cheng et al studied the evaporation of the linear diblock copolymer solution droplet using the implicit solvent MD simulation combined with the moving interface method . They further point out that the coffee-ring structure is hard to be observed without considering the flow inside the droplet.…”

Inducing stratification of colloidal mixtures with a mixed binary solvent

“…22 Fortini et al later discovered the unexpected small-on-top stratification in the case of extremely fast drying rates. 23 This discovery has triggered a series of experimental, [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] theoretical, [40][41][42][43][44][45] and computational [46][47][48][49][50][51][52][53][54][55][56][57][58] studies to reveal the underlying physical mechanism. It is now generally believed that the small-on-top stratification can be explained on the basis of diffusiophoresis, where colloidal particles are driven by the concentration gradient of other solutes (e.g., another type of particles) in the suspension.…”

Evidence of Size Stratification in Colloidal Glass Microgranules Realized by Rapid Evaporative Assembly

“…The nature of jamming of the nanoparticles, and thus their positional correlation in the assembled granules, is complex enough and primarily governed by the two competitive diffusional processes [(i) the osmotic pressure gradient and (ii) thermo-diffusion, which is known as the “Soret effect”] and the capillary force during droplet shrinkage. These diffusion processes depend on the size of the nanoparticles and the physiochemical properties of the colloidal dispersion; however, the kinetic effects in such a nonequilibrium process can give rise to kinetic trapping and thus can lead to stratification , during rapid jamming of the polydisperse colloidal particles. Furthermore, the possibility of formation of local clusters , during assembly adds to the configurational complexity.…”