Multiscale Modeling and Simulations of Polyelectrolyte Multilayers and Polyelectrolyte Complexes

Date

2023-9-11

Author

Özdemir, Erhan

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Polyelectrolytes are a unique class of polymers that can bear ionizable groups and, hence, can dissociate into ions when dissolved in a solvent, typically water. Polyelectrolytes can exhibit self-assembly behaviors, leading to many nanostructures, such as micelles and hollow spheres, that can be used in diverse applications like drug delivery, sensors, electronics and smart coatings. Layer-by-layer (LbL) assembly can also be used to prepare materials with tuned shapes or properties specific to the desired application. The significance of polyelectrolytes is vast, as they find applications in numerous fields. Hence, understanding polyelectrolytes at the molecular level is essential for their practical applications. Taking a broad view, the advantages of computational methods at different scales were combined to understand better the role of PEs in three different applications at the molecular level in this thesis study. In the first part of this thesis, modeling and simulation of polyelectrolyte multilayers with all-atom (AA) and coarse-grained (CG) molecular dynamics (MD) simulations were performed for operating as a substrate in Surface Enhanced Raman Spectroscopy (SERS) applications. It was demonstrated that the structure parameters of these polyelectrolyte multilayers (PEMs), the type of the polyelectrolyte and the number of layers affect the mobility of the nanoparticles used in SERS substrates and distribution of analyte on the surface. This makes PEMs convenient for preparing optimum substrates by tuning the surface morphology. In the second part, the effect of acid and solvent treatment on PEDOT:PSS was studied by first principle methods and MD simulations. The major finding in this part was the perfectly uniform distribution of HSO4- anions as a dopant in PEDOT crystalline structures in charge of the conductivity enhancement. In addition, insulating layers of PSS-H and PSS-Na can be washed away with the solvent, leading to an increase in electrical conductivity. In the last application, insoluble deposit formation in lubricant oil was modeled for the first time in the literature. Interactions between the constituents of the deposit model, detergent and dispersant were calculated by first principle calculations, and AA and CG MD simulations unraveled the role of detergents and dispersants in the deposit formation control.

Subject Keywords

Polyelectrolytes, Molecular Dynamics Simulations, Surface Enhanced Raman Spectroscopy, Electrical Conductivity, Lubricant Oil Additives

URI

https://hdl.handle.net/11511/105601

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Graduate School of Natural and Applied Sciences, Thesis