Browsing by Author "Ramezani Bajgiran, Shahryar"

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    Synthesis and physical behavior of weak polyelectrolyte brushes
    (2024-04-16) Ramezani Bajgiran, Shahryar; Marciel, Amanda B; Verduzco, Rafael
    Weak polyelectrolyte brushes (PEBs) consist of weakly charged polymers grafted to a surface and have emerged as promising candidates for responsive coatings due to their remarkable ability to undergo significant swelling and deswelling in response to changes in pH and ionic strength. This unique property holds immense potential for diverse applications in separation processes, drug delivery, and biosensing. The full potential of weak PEBs, however, is hampered by an incomplete understanding of their swelling behavior in response to various stimuli. Moreover, it has been shown that the swelling behavior of weak PEBs has a hysteretic memory response. This phenomenon manifests as a distinct difference in the swelling response when increasing or decreasing the pH, leading to unpredictable and unreliable performance in practical applications. To address these challenges, a comprehensive understanding of the physical factors that govern the swelling behavior of weak PEBs is essential. In this work, we investigated how pH, salt, and ionizable monomer fraction influence weak PEB swelling behavior. We synthesized a series of weakly charged polybasic brushes with varying fraction of ionizable monomers using an environmentally friendly surface-initiated polymerization technique with superior control and reproducibility over the polymerization kinetics. We used spectroscopic ellipsometry (SE), atomic force microscopy (AFM), and surface zeta potential measurements to characterize the swelling behavior and charge state of the brushes. We found that the pH-dependent swelling and hysteretic behavior of weak PEBs significantly increase as the fraction of ionizable monomers increases. Whereas salt concentration results in a complex non-monotonic swelling and hysteretic behavior. Lastly, to better understand the transport of particles within weak PEBs, we used a 3D super resolution tracking technique on a model charged tracer. We uncover significant spatial heterogeneities and find two distinctly different modes of motion within a weak PEB. Overall, our findings on the swelling behavior of weak PEBs and their interactions with particles can facilitate the design of more efficient stimuli-responsive coatings that use weak PEBs in various applications.