Controlling soft materials self-assembly through macromolecular design and solvent processing: theory and simulations
Date
2019
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Controlling the structure and self-assembly of polymers and soft materials is a key step in enabling their application as functional materials for technology, human health, and the environment. To satisfy performance metrics for these diverse applications, researchers are constantly developing new polymer chemistries, macromolecular architectures, assembly paradigms, and processing approaches. However, controlling the interplay between equilibrium driving forces and kinetic limitations in polymer and colloidal self-assembly, though crucial to appropriately harnessing these new techniques, remains a challenge. In this thesis, we apply coarse-grained molecular dynamics (CG-MD) simulations and liquid state theory to probe the interplay between two complementary approaches to control polymer and colloidal self-assembly: tuning the intra- and inter-molecular interactions that drive assembly via manipulating the molecular-level design of a macromolecule, and controlling the thermodynamics and dynamics of a soft material via solvent processing techniques. Specifically, we examine the effects of changing polymer architecture (e.g., linear, cyclic, star) and chemistry (e.g., the balance of hydrophobic vs. hydrophilic segments in an amphiphilic macromolecule) on the structure and thermodynamics of soft materials in a variety of solution environments. ☐ In the first part of the thesis, we discuss our efforts to develop and implement computational methods that facilitate the study of polymers in solution. We implemented and extended two complementary methods for phase equilibria simulations in the Gibbs ensemble, which we subsequently used to study polymer-solvent phase behavior. We also developed a Python-based implementation of Polymer Reference Interaction Site Model (PRISM) theory, a liquid-state theory technique to efficiently obtain structural and thermodynamic information in polymer and nanoparticle systems. Our goal in developing this open-source software (pyPRISM) was to lower the barrier for entry for the use of PRISM theory in the soft materials sciences. In the second part of the thesis, we apply these simulation and theory methods to uncover the structure (polymer chain configurations, polymer-polymer and polymer-solvent spatial correlations) and thermodynamics (polymer-polymer and polymer-solvent interactions) in polymer solutions of varying chain architecture. We probed these quantities as a function of polymer concentration and solvent quality, and rationalized the results based on the local environment of the monomers within the polymer chains. In the third part of the thesis, we present two examples of work combining simulations and experiments to explore the solution processing of bio-inspired soft materials for nanotechnology applications. In one aspect, we used a reverse emulsion assembly technique to prepare melanin-based nanostructured materials for optical applications. Our CG-MD simulations helped to understand the key driving forces controlling the surface structure of the colloidal assemblies. In the second aspect, we probed the aqueous assembly of DNA-containing amphiphilic molecules into novel nanotube structures for DNA nanotechnology applications. ☐ The cross-section of work highlighted herein spans a range of fields, from computational method development, to fundamental polymer physics, to applied nanotechnology and nanomaterials development. In each case, we designed appropriate CG models and simulation protocols to capture the key macromolecular driving forces for assembly and mimic the relevant solvent processing techniques. Then, we synergistically applied simulations, theory, and experiments to elucidate the mechanistic pathways that underlie the assembled structures. In this thesis, we hope to highlight several diverse examples where our combined simulation/theory/experiment approach can assist in the development of new functional materials for technological and societal impact.
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Keywords
Polymers, Self-assembly, Simulation & theory, Soft materials