[CCoE Notice] Dissertation Announcement: Xin Yuan, "Simulation of Weak Polyelectrolyte Brushes"

[Greenwell, Stephen J]

[Dissertation Defense Announcement at the Cullen College of Engineering]
Simulation of Weak Polyelectrolyte Brushes

Xin Yuan

April 28, 2025; 10 a.m. to 12 p.m.
Location: Engineering Building 1, Room S234

Committee Chair:
Jeremy C. Palmer, Ph.D.
Committee Members:
Jacinta C. Conrad, Ph.D. | Gül Zerze, Ph.D. | Amanda B. Marciel, Ph.D. |
Harold W. Hatch, Ph.D.
Abstract
Using molecular simulations, the stimuli-responsive behavior of weak polyelectrolyte brushes (PEBs) and weak polyampholyte brushes (PABs) was examined with respect to pH, salt concentration, monomer sequence and grafting density. While PEBs have only acidic or basic monomers, PABs contain both types of monomers, resulting in more complex interactions that require advanced simulation methods to properly investigate. As expected, the simulation results of PEBs are qualitatively consistent with previous experimental and theoretical studies, showing a crossover from the "osmotic" brush regime into the "salted" brush regime as salt concentration is increased. In contrast, the ionization state, brush height, lateral structure, and chain conformations of PABs vary with pH and salt concentration in ways that are qualitatively different from PEBs. While grafting density has a moderate impact on the response of PABs, monomer sequence and salt concentration play significant but different roles depending on pH conditions. At extreme pH conditions, salt concentration has a more prominent effect on PABs, because only one type of monomer is charged, and electrostatic repulsion is the dominant factor. Within the neutral pH range, monomer sequence becomes more important in regulating brush behavior due to electrostatic attractions prevailing when all acidic and basic monomers are charged. The findings in this work indicate that monomer sequence and salt can be leveraged to adjust the pH response of weak PABs to achieve the desired outcome when designing stimuli-responsive materials.
[Engineered For What's Next]


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