Counteranion-Specific Hydration States of Cationic Polyelectrolyte Brushes

Abstract

While polyelectrolyte brushes have received extensive attention due to their particular surface properties, the ion-specific hydration states remain largely unknown. Here, we report the counteranion-specific hydration states of cationic poly­[2-(methacryloyloxy)­ethyltrimethylammonium] (PMTA) brushes in salt-free water. The water droplet contact angle on the PMTA brushes depends on the counteranion species, and the order is consistent with the Hofmeister series. Weakly hydrated chaotropic counteranions are strongly bound to weakly hydrated quaternary ammonium (QA+) cations in the PMTA brush chains, which induces a reduction in the ζ-potential, dehydration, and collapse of the PMTA brushes. The PMTA brushes with strongly hydrated chloride counteranions produce a more diffuse tail and less swollen bound layer under salt-free deuterium oxide than brushes with weakly hydrated thiocyanate counteranions. Ion pairing disturbs the ordering of hydrated water in the PMTA brushes. Our work enhances the understanding of the ion specificity in the hydration states of polyelectrolyte brushes and encourages the rational design of charged polymer materials.

Interplay of Solvation and Size Effects Induced by the Counterions in Ionic Block Copolymers on the Basis of Hofmeister Series

“…In general, change of hydrophilicity of corona segment caused by ion exchange is essential to the morphological transitions. Usually, the counterions in the right of Hofmeister series will result in a more hydrophobic corona because of the decreasing of the solvation, resulting in a lower solubility of the q (P4VP)‐X block in water . This change of hydrophilicity of q (P4VP)‐X block can be proved by contact angle test since the corona blocks are on the shell of the assemblies.…”

“…Usually, the counterions in the right of Hofmeister series will result in a more hydrophobic corona because of the decreasing of the solvation, resulting in a lower solubility of the q(P4VP)-X block in water. [53,62] This change of hydrophilicity of q(P4VP)-X block can be proved by contact angle test since the corona blocks are on the shell of the assemblies. As shown in Figure 4, the water contact angles of PS 87 -b-q(P4VP 65 )-X films indeed increase from 30.5° for Br,ˉ to 42° for Iˉ, to 45.5° for SCNˉ, and to 47° for PF 6ˉ, respectively.…”

“…For Hofmeister ion series, the order of anion follows the sequence: SO 4 2 ˉ > OHˉ > Fˉ > Clˉ > Brˉ > NO 3 ˉ > Iˉ > SCNˉ > ClO 4 ˉ > PF 6 ˉ . Usually under similar conditions, the anions to the left are highly water soluble, while the anions to the right enable the ionic block to be more hydrophobic .…”

“…[ 53,54] Usually under similar conditions, the anions to the left are highly water soluble, while the anions to the right enable the ionic block to be more hydrophobic. [36,55,56] Herein, we intend to explore the effect of different counterions on the morphology of various aggregates by simple ion exchange in aqueous solution.…”

Transforming protein-polymer conjugate purification by tuning protein solubility

“…3 ) and at pH 7, would be 15% protonated and positively charged which was enough charge to keep CT soluble. Typical polyelectrolyte polymers collapse in high salt concentrations by screening of electrostatic interactions, but remain hydrated, which would have prevented precipitation 60 . There are many other types of monomers, both commercially available and that can be synthesized in-house, that are amenable to grafting-from techniques, namely ATRP or reversible addition-fragmentation chain-transfer (RAFT) polymerization.…”