Theoretical and Computational Modeling of Soft Materials

North Dakota State University Fargo, Fargo ND

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical studies and educational activities in the interdisciplinary field of soft materials science. Soft materials, such as colloidal dispersions and polymer solutions and melts, display remarkable thermal, mechanical, and optical properties that emerge from self-assembly of macromolecules into diverse structures. Predicting and controlling the structure, phase behavior, and dynamics of such materials require a deep understanding of the forces and correlations between macromolecules. Recent experimental observations demonstrate that strong ion-ion coupling, incorporation of nanoparticles, and application of external fields can profoundly influence the self-assembly of colloidal and polymeric materials. Motivated by these experiments, this project addresses several technologically relevant issues regarding the behavior of colloid-nanoparticle suspensions and polymer-nanoparticle composites. Specifically, the research will address the following fundamental questions: (1) Through what mechanisms can nanoparticles affect the stability of colloidal suspensions? (2) By tuning interparticle interactions, can we predict and control how nanoparticles perturb polymer conformations and induce coils to swell or shrink? (3) How should external fields be configured to guide self-assembly of soft materials? These unresolved questions will be addressed through a coarse-grained modeling approach that combines a variety of statistical mechanical methods. Poisson-Boltzmann theory, effective-interaction theory, classical density-functional theory, and Monte Carlo simulations will be developed and applied to probe length and time scales that are inaccessible to ab initio simulations. The ultimate goal of this research is to advance fundamental understanding of soft matter to the point of facilitating discovery and fabrication of novel, multifunctional, and environmentally sustainable nanostructured materials. Guiding the self-assembly of colloids, nanoparticles, and polymers has many potential applications. For example, enhancing phase stability of colloidal suspensions can aid the design and fabrication of photonic band-gap materials for optical switching. Engineering nanoparticles with tailored properties holds promise for modifying morphology of soft materials and controlling drug delivery. Understanding crowding of proteins by macromolecules within the cytoplasm has profound implications for manipulating the functions of biological cells. Furthermore, since suspensions of colloids and nanoparticles evolve slowly and can be imaged in real space, they can yield insights into the behavior of hard materials. Finally, the methods developed for colloidal and polymeric systems can be adapted to biologically relevant systems, such as biopolymers, virus suspensions, and polyelectrolyte microgels and microcapsules. Educational impacts of this project include training of undergraduate students and a postdoctoral fellow in soft matter physics and computational modeling methods; development of courses for graduate students in physics and interdisciplinary materials science programs; and support of outreach programs for local schools and Native American students throughout the state of North Dakota. NONTECHNICAL SUMMARY This award supports theoretical studies and educational activities in the interdisciplinary and technologically relevant field of soft materials science. Soft materials, which are composed of giant molecules called macromolecules, display remarkable physical properties that emerge from spontaneous organization of diverse structures. Common types of macromolecules are colloids, which are an ultra-divided form of matter consisting of particles some one-thousandth to one-millionth the size of the human hair, and polymers which are long chain-like molecules making up many natural and synthetic materials. Charge-stabilized colloids pervade industry and nature: familiar examples include aqueous paints, detergents, and clays, to name a few. Polymers are the building blocks of such ubiquitous materials as plastics and rubbers, and are key components of biomaterials including DNA and proteins. Predicting and controlling the behavior of soft materials requires a deep understanding of the highly tunable forces acting between macromolecules. Recent experimental observations demonstrate that incorporation of nanoparticles and application of external electric or magnetic fields can profoundly influence the self-assembly of colloidal and polymeric materials. Motivated by these experiments, this project applies an array of theoretical and computer modeling methods to address technologically relevant issues regarding the physical behavior of colloid-nanoparticle suspensions and polymer-nanoparticle composites. By clarifying several technologically important issues, outcomes of this work are expected to have broad significance for materials scientists and engineers by providing powerful tools to rationally design novel materials with potential applications to renewable energy and medicine. Furthermore, since suspensions of colloids and nanoparticles evolve slowly and can be imaged in real space, they can yield insights into the behavior of hard materials. Finally, the modeling methods developed will be broadly adaptable to a variety of macromolecular systems, including biological materials. Educational impacts of this project include training of undergraduate students and a postdoctoral fellow in soft matter physics and computational modeling methods; development of courses for graduate students in physics and interdisciplinary materials science programs; and support of outreach programs for local schools and Native American students throughout the state of North Dakota.