Studying phase separation in polymer systems through coarse-grained molecular dynamics simulations in MATILDA.FT

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Degree type
PhD
Graduate group
Physics and Astronomy
Discipline
Physics
Subject
Molecular Simulation
Polymer Physics
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Copyright date
01/01/2025
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Jedlinska, Zuzanna
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Abstract

Phase separation is a phenomenon consider to some degree in most of the research projects from the field of polymer physics. A special kind of phase separation, called liquid-liquid phase separation (LLPS) is of major importance to the functioning of biological systems. Frequently, phase separation results in a polymer lean solvent phase and the polymer rich, dense phase. However, the results of LLPS are two phases that both maintain their liquid-like properties. This liquid-like behavior of the components makes the process of LLPS fast and responsive to the changes in the environment, thus making it suitable to control the metabolism of the cells and allow them to respond to external stimuli. Intracellular condensates, created though LLPS, consist mostly of proteins, which are biomolecular polymers. Specifically, these condensates are enriched in special types of proteins, which either contain multiple intrinsically disordered regions (IDRs) or polypeptides which lack a higher order structure entirely - intrinsically disordered proteins (IDRs). We begin this thesis by providing an introduction to the topic of LLPS and IDPs. We discuss the role that the resulting condensates perform in the cells. Next, we focus on the structure and properties of their constituent IDPs. We outline how experimental, theoretical and computational methods are utilized to better understand LLPS and IDPs, listing the advantages and limitations of these methods. Lastly, we briefly introduce our groups own simulation software, MATILDA.FT, comparing it to other existing simulation packages, and showing its suitability to be used in the research concerned with LLPS.In Chapter 2 we provide an in-depth description of MATILDA.FT, its mathematical basis and algorithm implementation. In the following chapters we present various cases where MATILDA.FT has been applied to simulate coarse-grained models of bio-inspired condensates. In Chapter 3 we begin with the project concerned with the influence of monomer charge and polarizability, on the extent of phase separation and microstructure development. In addition, we in this project we also study the distribution of ions and their affinity towards polarizable and non-polarizable monomers. Subsequently, in Chapter 4, we describe a project in which we utilize dynamic bonding to induce phase separation. Dynamic bonds are relevant to both polymer materials (self-healing materials, responsive materials, sensors) and biological systems (abundance of hydrogen bonding, salt bridges, π-π, along with many other weak interactions). We show that we are able to control the extent of phase separation by changing the number and distribution of binding sites on the polymer chains. We also vary the affinity energy of bond creation, and analyze the changes in the static and dynamic properties of dynamic networks. In Chapter 5, we expand on the idea of binding-induced phase separation. We construct the systems consisting of polymer blends where chains can carry one of the two orthogonal binding sites. We show that by tuning the number of binding sites on the chains and their affinity energy, we are able to induce phase separation, resulting in two phases, each enriched in the monomers belonging to one of the binding types. We also study blends where cross-binding chains are present, which can carry binding sites of both types.

Advisor
Riggleman, Robert, A
Date of degree
2025
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