Absorbed weak polyelectrolytes: Impact of confinement, topology, and chemically specific interactions on ionization, conformation free energy, counterion condensation, and absorption equilibrium

Abstract

Absorption of weak polyelectrolytes impacts on properties such as ionization, conformations, and counterion (CI) condensation that are important in several areas of applied and fundamental science. We used a weak polyelectrolyte model and Monte Carlo simulations to investigate how the mentioned properties depend on pH or the size of a spherical cavity (SC) permeable to CIs but not to polyelectrolytes; the latter have either linear or starlike topologies and may be allowed to form charged hydrogen bonds (c H-bonds) between ionized and neutral monomers. Average ionization decreases upon increasing the number of arms at a constant number of monomers; it instead increases with the arm length in large SC due to CI screening. The way SC size, c H-bonds, and pH values interrelate to define ionization is instead more complicate due to arm pairing or clustering when c H-bonds are possible. These induce oscillations in the arm local ionization and impact on both monomer and CI distributions in the complete simulation cell in a way that also depends on polymer topology. The impact of ionization on the confinement free energy is also estimated; this highlighted that c H-bonding may enhance absorption compared with neutral chains.

Interface Counterion Localization Induces a Switch between Tight and Loose Configurations of Knotted Weak Polyacid Rings despite Intermonomer Coulomb Repulsions

“…More interestingly, the behavior of R g 2 versus α depends on ring topology. So, R g 2 for 0 1 monotonically increases upon increasing α due to Coulomb repulsion paralleling linear and starlike polyelectrolytes 23 or even nanogels. 45 Conversely, R g 2 of the other rings initially increases with α until α ≃ 0.75 ÷ 0.85, and it decreases for higher ionizations.…”

“…The relationship between ionization degree (α) and weak polyelectrolyte conformations has been the subject of many previous experimental − and theoretical − studies. On the whole, there is general consensus on the fact that polyelectrolyte persistence length increases upon increasing α, , unless chemically specific interactions (e.g., charged hydrogen bonds − or complexation/coordination of multivalent ions − ) may be formed as a consequence of polymer ionization.…”

Tunable Knot Segregation in Copolyelectrolyte Rings Carrying a Neutral Segment

“…41 Other relevant physical properties could be tuned along with chemical composition to influence the barriers for pinning or localizing knots, such as the total contour length of the ring, 42 the background ionic strength 33 of the solution, or the solvent quality. Besides, intrinsically short-ranged attraction in a neutral block (e.g., the ones due to a limited solvophilicity or the ability to form intrachain chemical specific interactions 43,44 ), may strengthen or even induce 41 the tendency to knot pinning, provided the NS is sufficiently long to position a few of its monomers in the regions facing each other in an essential crossing.…”

Can Oppositely Charged Polyelectrolyte Stars Form a Gel? A Simulational Study

“…However, more complicated situations like adding different ion types as mono-or even multivalent ions (e.g., in order to increase bond strengths by divalent ions bridging), changing the ionic block from being a strong polyelectrolyte to a weak polyelectrolyte and adding thus the possibility of the charged groups to respond to pH or to form inter-molecular charged hydrogen bonds [63][64][65] , or introducing polydispersity in arm length or in charged block length can easily be simulated with more refined models, and these systems are currently under investigation. The experimental realization of some of such systems is currently pursued in the group of F. H. Schacher 66 .…”