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    Effect of Ethanol and Urea as Solvent Additives on PSS-PDADMAPolyelectrolyte Complexation

    Journal: Macromolecules, Volume 55, APR 26, page 3140–3150

    Authors: Khavani, Mohammad; Batys, Piotr; Lalwani, Suvesh M.; Eneh, Chikaodinaka, I; Leino, Anna; Lutkenhaus, Jodie L.; Sammalkorpi, Maria

    Organizations: Academy of Finland through its Centres of Excellence Programme (2022-2029) [346111, 309324]; Business Finland Co-Innovation Grant [3767/31/2019]; National Science Centre, Poland [2018/31/D/ST5/01866]; National Science Foundation [1905732]; FinnCERES Materials Bioeconomy Ecosystem; Division Of Materials Research; Direct For Mathematical & Physical Scien [1905732] Funding Source: National Science Foundation

    The effect of urea and ethanol additives on aqueous solutions of poly(styrenesulfonate) (PSS), poly(diallyldimethyl-ammonium) (PDADMA), and their complexation interactions are examined here via molecular dynamics simulations,interconnected laser Doppler velocimetry, and quartz crystal microbalance with dissipation. It is found that urea and ethanolhave significant, yet opposite influences on PSS and PDADMA solvation and interactions. Notably, ethanol is systematically depletedfrom solvating the charge groups but condenses at the hydrophobic backbone of PSS. As a consequence of the poorer solvationenvironment for the ionic groups, ethanol significantly increases the extent of counterion condensation. On the other hand, ureareadily solvates both polyelectrolytes and replaces water in solvation. For PSS, urea causes disruption of the hydrogen bonding of thePSS headgroup with water. In PSS-PDADMA complexation, these differences influence changes in the binding configurationsrelative to the case of pure water. Specifically, added ethanol leads to loosening of the complex caused by the enhancement ofcounterion condensation; added urea pushes polyelectrolyte chains further apart because of the formation of a persistent solvationshell. In total, wefind that the effects of urea and ethanol rise from changes in the microscopic-level solvation environment andconformation resulting from solvating water being replaced by the additive. The differences cannot be explained purely viaconsidering relative permittivity and continuum level electrostatic screening. Taken together, thefindings could bear significance intuning polyelectrolyte materials'mechanical and swelling characteristics via solution additives.
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