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NONTECHNICAL SUMMARY
This CAREER award supports computational and theoretical research, and education on the physics of evaporative drying of soft matter solutions. Paint is an example of soft matter solution. Paint is a particle suspension, which is a heterogeneous mixture of little particles suspended throughout the bulk of a solvent. A polymer solution is another example, which is a mixture of a solvent and polymers, long-chain molecules, dissolved in it. The drying process of these soft matter solutions provides a way to fabricate materials and a way to investigate physics in systems out of equilibrium. A famous illustration is the coffee ring effect, where a spill of coffee, a particle suspension like paint, leaves a ring-like deposit at its perimeter after drying. As another example, novel stratification phenomena have recently been discovered in suspension films containing particles of varied sizes, where the particles are found to form stratified layers according to their sizes after the suspensions are rapidly dried. The goal of the research is to use computer simulation techniques and simple physical models to elucidate the collective behavior of particles intrinsic to the evaporation processes of particle suspensions, polymer solutions, and their mixtures, and to map out the optimized drying conditions under which the resultant materials have desired structures. Such materials include multi-layered thin films of particles or polymer and composite materials with particulate fillers dispersed through a polymer matrix in a controlled manner. Specifically, this project aims to answer the following questions: How are the dissolved or dispersed components distributed in the dry film after a solution containing a mixture of solutes is dried quickly? How do particles and polymers migrate under concentration, temperature or other gradients that naturally emerge in a drying process? The findings will be used to guide the design of new solvent evaporation processes for more efficient material fabrication. The project integrates research into education and outreach activities that involve high school, undergraduate, and graduate students, high school and college educators, and the broader public. Specific goals include establishing a soft matter curriculum at Virginia Tech, cultivating students and future workforce with this curriculum, fostering the growth of a soft matter community in Virginia, and promoting the emerging concept of “material discovery accelerated through complementary efforts in computation, theory, and experiment” to the general public.

TECHNICAL SUMMARY
This CAREER award supports computational and theoretical research, and education on the physics of evaporative drying of soft matter solutions. Solvent evaporation out of colloidal and polymer solutions and their mixtures is a tool frequently used to fabricate thin film materials, but our understanding of how the evaporation process of the solvent impacts the structures of the final colloidal and polymer films is largely based on experience and lacks predictive capabilities. The overarching objective of the research component is to use tools in nonequilibrium statistical mechanics to map out the optimized evaporation conditions under which the drying colloidal and polymer solutions yield materials with desired structures, including stratified colloidal thin films, layered polymer thin films, and polymer nanocomposites with controlled dispersion of nanoparticles. Adopting a hybrid computational/theoretical approach, the PI uses particle-based descriptions of liquids, colloidal particles, and polymers to probe the rich nonequilibrium, many-body physics intrinsic to evaporation processes. The main goal is to use molecular dynamics techniques to model the drying process of various soft matter solutions with an explicit solvent based on Lennard-Jones liquids or water in coarse-grained representations, and to reveal the effects of evaporation processes on the resulting material structures. These effects are challenging to evaluate with current experiments. Specifically, the PI aims to elucidate the physics of drying-induced stratification in various multicomponent soft matter solutions and the phoretic response of particles and polymers to concentration, temperature, chemical potential, and other gradients that emerge during the drying process. Studying solvent explicitly enables the PI to identify cases where an implicit solvent model might be appropriate, which can serve as a guidance for many other researchers who lack the resources to model a solvent explicitly for drying solutions. The project integrates research into education and outreach activities that involve students, educators, and the broader public and aim to establish a soft matter curriculum at Virginia Tech, to cultivate students and future workforce with this curriculum, to foster the growth of a soft matter community in Virginia, and to promote nonequilibrium physics and the emerging concepts of “computational thinking” and “materials via self-assembly” to the general public.

This award reflects NSF’s statutory mission and has been deemed worthy of support through evaluation using the Foundation’s intellectual merit and broader impacts review criteria.

Detailed Award Information

Award Information:
Title: CAREER: Nonequilibrium Physics in Drying Soft Matter Solutions
ID: 1944887
Effective Date: 06/01/2020
Expiration Date: 05/31/2025
Amount: $514,786

Institution Information:
Name: Virginia Polytechnic Institute and State University
City: Blacksburg
State: VA
Country: United States
MSI: Other Institution

Investigator Information:
Role Code: Principal Investigator
Name: Shengfeng Cheng
Email Address: chengsf@vt.edu

Organization Information:
Directorate: 4900
Division: NSF

Program Information:
Code: 4900
Text: CONDENSED MATTER & MAT THEORY