Effects of polymer architecture on amphiphilic polymer self-assembly: molecular simulations and computational analysis of scattering experiments
Date
2021
Authors
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Publisher
University of Delaware
Abstract
Understanding the structure and thermodynamics of assembly of amphiphilic polymers is key to the design and application of functional materials in healthcare, energy, and nanotechnology fields. The recent advances in polymer synthesis have enabled tailoring and fine tuning of amphiphilic polymer design towards development of materials that exhibit the desired properties needed for application in these diverse fields. The resulting large polymer design space has created a need for the development of rational design rules, thus motivating researchers to synergize and integrate synthesis and characterization techniques with molecular modelling and simulations. This doctoral research dissertation has been focused on the development and application of coarse-grained molecular dynamics (CG-MD) simulations to build rational design rules (e.g., choice of solvent chemistry as well as polymer sequence, chemical composition, architecture, etc.) for amphiphilic polymer solutions with validation from experiments conducted in our collaborators’ laboratories. In this dissertation I also present the development and implementation of a new computational method called computational reverse engineering analysis of scattering experiments (CREASE) to analyze and interpret experimental characterization of structure in amphiphilic polymer solutions. ☐ In the first part of this dissertation, I discuss my development of appropriate CG models for the amphiphilic polymer chemistries with branched architectures studied in our experimental collaborators’ laboratories. These CG models are used in MD simulations to investigate shapes and sizes of the assembled structures and the thermodynamics of self-assembly in solutions of these branched amphiphilic polymers. First, I describe the CG-MD study of one specific class of coil-brush diblock amphiphilic polymers synthesized in our collaborators’ laboratory. Then, I describe how we extend this CG-MD simulation approach to explore a larger set of architectures, composition, and sequence to develop design rules linking polymer design to the assembled structures in solution or near/on solvophobic surfaces. I also compare a sub-set of results from CG-MD simulations with analogous systems’ results from Polymer Reference Interaction Site Model (PRISM) theory; the PRISM theory calculations were completed by Dr. Ivan Lyubimov in my research group. This comparison between CG-MD simulations and PRISM theory establishes the potential for using relatively fast PRISM theory calculations to scan large polymer design spaces in a computationally efficient manner to identify the most relevant design parameters that can then be simulated using CG-MD simulations. ☐ In the second part of this dissertation, I present the development and application of CREASE to analyze and interpret structure from small angle scattering characterization of amphiphilic polymer solutions with spherical, cylindrical, elliptical cylindrical, and fibrillar micelles. While existing methods of analysis for more unconventional shapes do not exist or are too approximate, CREASE is able to analyze them and provide structural information at the chain and monomer level. I demonstrate the success of CREASE by presenting multiple cases where the dimensions obtained from the application of CREASE to small angle scattering results from in vitro experiments matched those obtained from microscopy techniques better than those obtained from conventional fits of scattering results with approximate analytical models. I also demonstrate how CREASE can be applied to analyze complex structures in cases where microscopy only hints at the shape of the assembled structure but does not provide dimensions. I conclude this part of the dissertation by integrating machine learning with CREASE to improve the computational speed and efficiency of the CREASE method. ☐ Overall, in this dissertation I describe work that demonstrates successful development and application of coarse-grained models, molecular simulations, and computational methods synergistically with experiments to predict nanostructures and understand self-assembly within branched amphiphilic polymer solutions.
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Keywords
CREASE, Polymer architecture, Polymer physics, Self-assembly, Small angle scattering