Browsing by Subject "Polyelectrolytes"

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    Polymer Solutions in Complex Flows: Fibrils, Filaments, and Flocs
    (2020-08) Metaxas, Athena
    The behavior of polymers in solution under complex physicochemical and hydrodynamic flow fields is of interest to a variety of industrial processes, such as polymer processing and water treatment. In this thesis, two main areas are presented: (1) self-association of polymer chains in flow, resulting in the formation of fibrils and filaments, and (2) association of polymer chains with suspended particulate, resulting in the formation of flocs. In the first area, extensional properties of methylcellulose (MC) solutions were characterized using millimeter scale capillary thinning and micrometer scale filament stretching methods. The addition of NaCl to MC solutions results in self-assembly of a fraction of the MC chains into MC fibrils, which imparts elastic characteristics to the solution. Capillary Breakup Extensional Rheometry (CaBER) studies demonstrate the extensional relaxation time and extensional viscosity increased with increasing MC concentration in the presence of salt. Likewise, microfluidic filament stretching studies demonstrate the extensional viscosity increased with increasing NaCl concentration. By reducing the characteristic length scale of the thinning filament, the microfluidic platform enabled new measurements extensional properties for low molecular weight and low viscosity MC solutions. In the second area, the assembly of charged polymers, or polyelectrolytes, with bentonite clay into flocs was studied in complex flow fields using macroscale Taylor-Couette (TC) flows. A custom-built TC cell allowed for injection of the polyelectrolyte solution into the particle-laden flow to investigate in-situ floc nucleation and growth in varied hydrodynamic flow states. Faster floc growth rates and decreased 2-D perimeter-based fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and shear rounding of the flocs, respectively. Additionally, the effects of ionic strength and polyelectrolyte molecular weight on flocculation in the TC cell were investigated. Smaller flocs were formed with increasing ionic strength, due to the role of charge screening on the initial bentonite aggregate size and polyelectrolyte chain persistence length and conformation in solution. Overall, this thesis seeks to provide additional understanding of how polymers assemble in solution under a variety of physicochemical conditions and flow, which can inform predictive processing capabilities and performance.
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    Simulation data for "Adsorption of Charge Sequence-Specific Polydisperse Polyelectrolytes"
    (2021-05-28) Sethuraman, Vaidyanathan; Zheng, David; Morse, David C; Dorfman, Kevin D; vsethura@umn.edu; Sethuraman, Vaidyanathan; Dorfman Lab
    Simulation data and codes for reproducing the data in the paper titled "Adsorption of Charge Sequence-Specific Polydisperse Polyelectrolytes".
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    Simulation data for "Influence of charge sequence on the adsorption of polyelectrolytes to oppositely-charged polyelectrolyte brushes"
    (2019-06-20) Sethuraman, Vaidyanathan; McGovern, Michael; Morse, David C; Dorfman, Kevin D; vsethura@umn.edu; Sethuraman, Vaidyanathan; Dorfman Group
    When a solution of polyanionic chains is placed in contact with a polycationic brush, the polyanions adsorb into the brush. We investigate the influence of the charge sequences of the free and bound species on the thermodynamics of polyelectrolyte adsorption. As model systems, we consider free and brush polyelectrolytes with either block or alternating charge sequences, and study the adsorption process using coarse-grained Langevin dynamics with implicit solvent, explicit counterions, and excess salt. Free energy, internal energy, and entropy of adsorption are computed using umbrella sampling methods. When the number of polyanions exceed the number of polycations, the brush becomes overcharged. Free chains adsorb most strongly when both free and tethered chains have a block charge sequence, and most weakly when both species have an alternating sequence. Adsorption is stronger when the free polyanion has a block sequence and the tethered polycation is alternating than in the reverse case of an alternating free polymer and a tethered block copolymer. Sequence-dependent effects are shown to be largely energetic, rather than entropic, in origin.