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Tailoring structure and properties of polyelectrolyte-based material via materials selection and post-assembly treatment Public

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Although polyelectrolyte-base materials have demonstrated uses in a wide range of applications, controlling properties of polyelectrolyte-based materials is challenging because of their sensitivity to material and processing parameters. This dissertation focused on fundamental science of polyelectrolyte-based materials. Although polyelectrolyte-based materials like PEMs and PECs have a wide range of potential applications, the relationship between structure and properties of those materials is still not fully understood. In this work, factors that can affect the structure and properties of PEMs and PECs were studied. Based on those results, potential approaches to tailor structure and properties of polyelectrolyte-based materials can be developed.\nThe role of the chemistry and molecular weight of first layer of a PEM was studied. By changing first layer materials, PEMs showed different internal structure, mass accumulation, and surface morphology. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the PEM assembly process. First layer choice affects the total mass accumulation of the PEM as well as the stoichiometry and thickness of the PEM. PEM topography is also affected by first layer choice. Combined with the stoichiometry results, these findings indicate that the structure of a PEM is fundamentally different depending on first layer chemistry and molecular weight. Selection of appropriate first layer material is therefore an important consideration in the design of a PEM and changing first layer material may be a facile way to tailor the structure and properties of PEMs.\nAnother category of polyelectrolyte-based materials, PECs, which are formed through electrostatic interactions between oppositely charged polyelectrolytes, have garnered sustained interest for their range of potential applications. Since water plays an important role in the structure and properties of polyelectrolyte-based materials, humidity controlled dynamic mechanical analysis (DMA) was used to characterize the thermomechanical properties of dried polyelectrolytes and PECs with different thermal and humidity histories. After exposure to higher humidities (humidity tempering), both room temperature storage modulus and flexural modulus of the resulting PEC increased. Water from the humid air plasticized the PEC, increasing mobility and facilitating chain reorganization during humidity tempering, which resulted in a structure with more intrinsic electrostatic bonds (cross-links) and higher moduli. Storage conditions and relative humidity were demonstrated to influence thermal transitions and mechanical properties of PEC, which highlighted the potential of polyelectrolyte-based materials for new applications where tailoring of mechanical properties is desired.

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  • 01/05/2021
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  • etd-042419-105520
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  • 2019
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  • 2019-04-24
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