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Chemical and Biomolecular Engineering

Charles Sing Research

Polymer Physics, Statistical Mechanics, and Computer Simulation

Sing Research Group

Polymers represent powerful chemical systems with which to develop highly-functional materials for a wide variety of uses, ranging from energy to biomedical to nanomaterial applications. Biological systems already utilize many of the unique physical properties of polymeric molecules (e.g. proteins, polysaccharides, DNA) as the foundation of intricate, hierarchical structures that make up living materials. Our group is inspired by biological systems, and we seek to develop new and designed materials that can emulate analogues in the biological realm. We desire new technologies that are capable of matching biological materials, since materials addressing the technological and societal challenges in modern science (the development and storage of energy, the delivery of a drug to a specific location, the assembly of complicated nano-scale structures, etc.) have yet to catch up to the sophistication of biological systems.

To provide new paradigms in bioinspired materials, we are interested in using a combination of polymer physics and computer simulation to provide quantitative and physical insight into molecular-level mechanisms to dictate structure or function in polymer systems. Projects in our group consider fundamental problems in polymer physics, however with an eye towards how they will be applied or leveraged to tackle real societal and technological problems as well as to interrogate specific biophysical problems. We are currently focusing on three primary research themes:

Charged Polymer Systems

A common motif in both biopolymers and synthetic polymers is the inclusion of charges; Coulomb interactions are known to lead to a rich array of physical behaviors that remain a crucial area of study within polymer physics. The importance of these systems on material applications is immense, with ramifications in a wide array of systems such as fuel cell and battery membranes, bio-inspired adhesives, drug-delivery vehicles, and self-assembled nanostructures; understanding these systems is crucial to addressing societal issues concerning green energy, sustainability, and health.

Charge organization can be used to tune polymeric systems, with dramatic effects seen due to polymer connectivity and molecular structure.

We will be leveraging recent advances in the study of charged systems to understand fundamental questions in charged polymer physics and elucidate new routes to designing nano-structured materials. For example, charged block copolymers can be used for designed membranes for energy-related devices, and understanding the effect of charges on structure is imperative to effective membrane design. Likewise, oppositely-charged polyions are currently being investigated for their self-assembly properties and their sensitivity to the local ion environment. We seek to further clarify design principles and physical intuition governing these systems, including understanding the role of molecular-level structural features.

Driven Polymers

Architecture can play a key role in single polymer dynamics. Topological constraints and branches (for example) can affect the dynamical behavior of these systems. Collaboration with the Charles Schroeder group seeks to fundamentally understand these effects.

Processing polymer materials involves deformations due to flows or stresses, and it is thus imperative to understand how polymers respond at a molecular level. In particular, using flows to manipulate polymeric materials can lead to driven assembly. This can work in concert with equilibrium self-assembly to guide the manipulation of these materials to new levels of complexity. Advances in kinetically driven systems using flows and fields provide an orthogonal way to tune systems that has yet to be fully explored, however is poised to revolutionize how we manipulate materials to exhibit properties desired for applications such as molecular organic electronics, drug delivery vehicles, and patterned substrates.

Our research is investigating the possibility that judicious and minimal design of monomer sequence or architecture can be coupled with driving fields and flows. This new level of control will enhance the ability to explore the conformational and structural organization of polymeric systems. We are interested in the fundamental connection between polymer dynamics, both at the single-chain and bulk level, and their molecular structure and properties (sequence, charge-based properties, architecture) in order to design new materials with tunable out-of-equilibrium properties. New theoretical and conceptual understandings that specifically take into account polymer structure and chemistry will allow the manipulation of polymers via the interplay between macroscopic controls and molecular-level features.

The conformational evolution of single polymer chains can be manipulated using flows and/or fields. Monomer sequence – even in block copolymers – has a profound effect on conformations in such out-of-equilibrium scenarios. We are developing simplified models that will elucidate underlying physical fundamentals that inform the design of polymer systems.

Biophysics and Bioinspired Materials

An abundance of biological materials such as mucin, von Willebrand Factor, and chromatin are known to display interesting physics on disparate time and length scales. We aspire to emulate these physical behaviors found in biological systems. For example, DNA-protein interactions enable DNA conformation to be dictated by proteins, but conversely the DNA itself will govern protein binding. We will be developing new models to look at larger-length scale cooperative properties of this DNA-protein interplay. We want to develop large scale computational models as well as a theoretical understanding of how proteins interact with genetic material to create a “computational probe” of large length scale biophysical processes and ultimately connect molecular interactions with physiological behaviors.

We aspire to subsequently use our theoretical insight to enable the design of molecular systems with novel properties. Specifically, we will use our understanding of elasticity and electrostatics in protein-protein interactions and DNA-protein binding such that we can subsequently apply these effects to designed materials that exhibit molecular biomimetic properties such as artificial allostery and ion-specific stimuli response. Using fundamental polymer systems, we ultimately aim to elucidate minimal schemes for the realization of “artificial signalling” where synthetically accessible materials can partake in elaborate regulatory processes to form “soft computers.”

Competitive binding of multiple species may couple to the properties of an underlying substrate. Coarse-grained models of biophysical processes will inspire the development of soft devices.
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