Shawn Mengel Ph.D. Defense

Date: 

Thursday, February 20, 2025 - 12:30pm

Location: 

Elings Hall 1601 | Zoom Link: https://ucsb.zoom.us/j/89961180562 | Meeting ID: 899 6118 0562

Speaker: 

Shawn Mengel

Title: Molecular Design and Hydration Behavior of Polymeric Zwitterions

Abstract: 

Fouling, or the accumulation of biological material onto surfaces, incurs significant operational costs and environmental challenges to industrial applications. In marine applications, biofouling on ship hulls increases fuel consumption, greenhouse gas emissions, and the spread of invasive species. In chemical manufacturing, biofilms, oils, and particulates clog water filtration membranes, hindering the economic viability of green separation processes through increased capital and maintenance. Polymeric zwitterions containing paired positive and negative charges show great promise for mitigating fouling due to their strong binding of water molecules, which act as a barrier to close approach and adsorption of foulants to the surface. While these zwitterionic materials have demonstrated impressive empirical performance across a range of applications, the molecular mechanisms driving their performance and the role of zwitterion molecular structure remain poorly understood.

This work links the molecular design of polymeric zwitterions to antifouling performance by examining the structure and dynamics of hydration and ion interactions at the interface. Two molecular parameters, the cation charge delocalization and the carbon spacer length between tethered ions, are studied. The effect of charge delocalization is probed using a combination of sum frequency generation (SFG) spectroscopy, Overhauser dynamic nuclear polarization (ODNP) relaxometry, and fouling assays with the green alga Ulva linza. Larger, more diffuse charges enhance hydration, improving marine antifouling performance as shown by reduced algal settlement and easier biomass removal upon washing. ODNP analysis reveals that charge delocalization strongly influences local water diffusion within the surface hydration shell, which is mediated by complex interactions with dissolved ions. Additionally, analysis of hydration in zwitterionic hydrogels provides a physical basis to the superior performance of zwitterions with short spacers between their cation and anion. Differences in swelling and salt partitioning suggest that zwitterions with long spacer units have more polyelectrolyte-like behavior, where appreciable surface charges can create attractive interactions with foulants. These findings provide molecular-level insights for designing next-generation antifouling materials, optimizing polymer hydration to mitigate fouling in marine and membrane applications.

Event Type: 

General Event