Investigating the Effect of External Conditions and Chemical Structure on Water Sorption and Dissociation and Cation Identity on Ion Transport and Selectivity in Weak Crosslinked Polyelectrolyte Membranes

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Author:
Kanumuru, Nikitha
Area of Honors:
Materials Science and Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Hee Jeung Oh, Thesis Supervisor
Amy Carol Robinson, Thesis Honors Advisor
Keywords:
Polymer
Titration
Membrane
PEGDA
Ion Exchange Capacity
pH
Acrylic Acid
FT-IR
Fundamental Properties
Ion Transport
Salt Permeability
Water Solubility
Abstract:
Charged polymer membranes have widespread applications in ionic separations, resource recovery, batteries, and desalination that can positively impact a diverse range of industries. To develop such technologies, fundamental understanding of water and transport properties is needed. In previous studies, strongly charged membranes made it difficult to observe the transport differences in membranes due to changes in chemical structures. To mitigate these challenges, we have designed acrylic acid-poly(ethylene glycol) diacrylate (AA-PEGDA) random copolymer network membranes with low water swelling and a wide degree of ion exchange capacity. This provides a tunable platform to study water solubility, chemical structure, salt permeability, degree of ionization, and other transport properties. We observed the effects of varying external solution pH on the dissociation and water sorption of our library of membranes and studied the effects of modifying chemical structure and ion exchange capacity. We found that higher solution pH led to higher water sorption and dissociation in the membrane’s charged group content. To study the differences in ion transport in different salts with representative cations, we used a fixed polymer composition and correlated salt permeability and selectivity values to external pH and water solubility. We found significant differences in salt permeability and selectivity due to ion hydration, valence, and size and found good agreement to free volume theory. We also studied the charged group content in the membrane using FT-IR and potentiometric titration calculations which showed significant differences in charged group dissociation. This research will help develop tailored technologies for a wide range of industries.