APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020;
Denver, Colorado
Session S68: Non-equilibrium Dynamics of Film Formation During Drying
11:15 AM–2:15 PM,
Thursday, March 5, 2020
Room: Four Seasons 4
Sponsoring
Units:
DPOLY DSOFT
Chair: Gary Grest, Sandia National Laboratories
Abstract: S68.00003 : Drying Process in Films of Nanoparticle Suspensions and Polymer Solutions*
Abstract
Presenter:
Shengfeng Cheng
(Virginia Tech)
Author:
Shengfeng Cheng
(Virginia Tech)
The drying process of polymer solutions or nanoparticle suspensions provides an excellent playground to explore nonequilibrium physics. For example, novel stratification phenomena have recently been discovered in polydisperse particle suspension films that undergo rapid drying. In these systems, the complex interplay of solvent evaporation, fluid dynamics, diffusion, phoresis, and capillarity leads to rich, far-from-equilibrium phenomena. I will describe our efforts using large scale molecular dynamics (MD) simulations to study the drying process of colloid suspensions, polymer solutions, and their mixtures. For bidisperse particle suspensions, a state diagram of stratification is determined and the counterintuitive "small-on-top" stratification, with an enrichment of the smaller particles at the receding liquid-vapor interface during fast drying, is observed. Results are compared to the predictions of several theoretical models based on diffusiophoresis. We show that the temperature gradient induced by evaporative cooling can lead to size-dependent thermophoretic responses of nanoparticles, which compete with diffusiophoresis and suppress the “small-on-top'” stratification. On the basis of this observation, an approach to control stratification using various externally imposed thermal gradients is suggested and validated with MD simulations. We further show that a mixture of two liquids stratifies when rapidly dried with the less volatile component concentrated near the evaporating interface. This phenomenon can be used to separate and stratify particles which have different couplings to the components of a liquid mixture. Finally, we demonstrate a new strategy of unfirmly dispersing nanoparticles into a polymer matrix using fast solvent evaporation, based on the stratification behavior of polymer-particle mixtures in a far-from-equilibrium situation induced by rapid drying.
*Computational hours are provided through a DOE ALCC award.