[CCoE Notice] Cullen College Dissertation Defense Announcement - Ali Slim

[Knudsen, Rachel W]

[Dissertation Defense Announcement at the Cullen College of Engineering]
Structure Controlled Dynamics of Particles and Polymers in Aqueous Polyelectrolyte Solutions

Ali Slim
May 2, 2022;  12:30 – 2:00PM (CST)

Location: MREB Building,  Agrawal Conference Room #126

Committee Chair:
Jacinta Conrad, Ph.D.
Committee Members:
Jeremy Palmer, Ph.D. | Alamgir Karim, Ph.D. | Devin L Shaffer, Ph.D. | Haleh Ardebili, PhD.
Abstract
          Complex fluids of particles and polymers can be found a wide range of industrial applications including enhanced oil recovery, drug delivery, and consumer goods. Polyelectrolytes are polymers with charged functional groups on their backbone. The charged groups allow polyelectrolytes to maintain high stability and good biocompatibility in aqueous solutions. The induced electrostatic repulsion, however, result in highly extended conformations compared to their neutral counterparts. The size, strength, and recurrence of these charged groups between the monomers leads to conformations ranging from rigid rod to semiflexible chain. These unique electrostatically-induced structural properties likely affect their relaxations as well as the transport of objects within their networks.
          We investigate the dynamics of particles and polyelectrolyte chains in semidilute aqueous polyelectrolyte solutions using a combination of optical microscopy and scattering techniques. We tune the structural properties of our system by varying concentration, ionic strength, and molecular weight. We show that particle dynamics non-monotonically deviate from ideal predictions. These deviations become larger as particles approach length scales relevant to chain size. Our findings propose the presence of confinement effects that are not observed in neutral systems, suggesting that the deviations in particle dynamics rise from the unique conformation of polyelectrolytes. Moreover, we demonstrate how the segmental relaxations of polyelectrolyte chains experience two qualitatively different scaling behaviors. At small length scales, chains relax according to theory. Chain dynamics, however, deviate at larger length scales with slower than predicted relaxations. The deviations start at the characteristic length scale chains, suggesting that the slower dynamics result from coupling to the chain structure, which introduces a free energy minimum that makes relaxations outside of it unfavorable. The physical pictures presented in this work will help control the transport of particles in complex media and grant better understanding of structural properties of polyelectrolyte materials.
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