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Materials Science Division

Theme II: Precision Synthesis and Characterization

Our group utilizes a wide array of microscopy, spectroscopy and scattering techniques to understand with particular attention to charged polymers including multivalent interactions, the phase behavior of complex coacervates, polymer brushes and micelles.

Designer Polymers

Polyelectrolyte complexes (PECs) form through associative phase separation of oppositely–charged polymers in aqueous settings. These ion-containing polymers can be tailored toward completely hydrophilic, compartmentalized assemblies in solution, depending on the chemical attributes, electrostatic interactions and arrangement of the constituent monomers. This positions them to encapsulate/transport challenging biomolecules such as nucleic acids or proteins, coat underwater surfaces with ionic surfaces, and repair tissues between skin and bone as biocompatible soft adhesives.

However, the functional roles of chemical and ionic interactions need to be mechanistically understood for translation into safe, effective and reliable end-use technologies. A materials–genome approach, based on expanding experimental and simulation datasets of PEC systems, can enable a more-diverse materials information infrastructure for understanding how specific non-covalent interactions prevail in polyelectrolyte behavior.

Our work aims to advance soft matter design based on charge complexation in micelle and hydrogel platforms. New synthesis–screening platforms have been pursued in a parallel synthesizer, facilitating the rapid preparation of well-defined block polyelectrolyte candidates. The complex formation, temporal evolution, and disassembly of structured PECs have been investigated with a wide range of solution phase characterization tools that our group specializes in to better predict and design specialized assemblies for emerging storage and delivery challenges in the biomedical landscape.

Macromolecules 53, 102-111 (2020) DOI: 10.1021/acs.macromol.9b01814

ACS Macro Lett. 7, 406411 (2018) DOI: 10.1021/acsmacrolett.8b00069

ACS Macro Lett. 7, 726733 (2018) DOI: 10.1021/acsmacrolett.8b00346

Structure of Dense Polyelectrolyte Brushes in the Presence of Multivalent Counterions

The response of polyelectrolyte brushes to specific environmental conditions has attracted materials scientists due to its relevance in biological systems and various applications in materials science and nanotechnology. We combined atomic force microscopy (AFM), SFA technique, and coarse-grained molecular dynamics (MD) simulations to study the structure of planar polyelectrolyte brushes (poly(styrene-sulfonate), PSS) in a variety of solvent conditions. AFM images directly visualized lateral inhomogeneities on the surface of polyelectrolyte brushes collapsed in solutions containing trivalent counterions, results that were fully supported by the coarse-grained MD simulations. We also observed that the presence of multivalent counterions (2+/3+) dramatically increased the friction forces between brushes. Our discoveries have the potential for far reaching impact in materials science for the development of stimuli-responsive nanoscale structured surfaces.

Science 460 (2018) 1434-1438

Water Filtration

As many resources are being unsustainably depleted as the global population exponentially rises, society is turning towards wastewater as a new source for reclaiming valuable nutrients. Novel materials need to be engineered to sequester and recycle these valuable resources for reuse, with phosphate as a key target for reuse as a fertilizer. This work specifically aims to design a new material based on biologically-inspired peptide amphiphiles (PAs) that can molecularly recognize, sequester and recycle phosphate out of water. To perform these functions, we are synthetically manipulating the natural ability of proteins to specifically bind to ions and small molecules based on their molecular sequence and secondary structure. Thus, we have incorporated phosphate-binding amino acid sequences into the peptide ​“headgroup” of PAs, which are conjugated to an alkyl ​“tail.” These molecules then spontaneously self-assemble into supramolecular structures that display the binding sequence to the aqueous environment. We have also programed these PA micelles to entangle and crosslink, creating a dense, gelled network of molecular-recognition structures that will retain phosphate at high pH and controllably release phosphate at low pH, as water is flowed through the hydrogel. This work utilizes a step-wise approach to exploit biological inspiration of protein binding to design and evaluate a synthetic material that can molecularly recognize, sequester and release phosphate, exploring fundamental reversible-binding knowledge for selective materials and paving the way for future designs of sustainable capture-and-release materials.

Abstracts of papers of the American Chemical Society, 258 Abstract number:448-PMSE (2019)