Crucial Nonelectrostatic Effects on Polyelectrolyte Brush Behavior

Abstract

Polyelectrolyte brushes have received extensive attention due to their swelling behavior in aqueous solutions, which is a result of their ionic nature and nonelectrostatic (polymer–polymer and polymer–solvent) interactions. While the nonelectrostatic contributions are typically assumed to be negligible compared to the ion osmotic pressure, we present herein a systematic investigation of how the nonelectrostatic interactions dramatically affect the swelling behavior of polyelectrolyte brushes. Using a modular synthesis procedure, polyelectrolyte brushes with similar chain lengths, grafting densities, and charge densities but with various side chains were synthesized. The swelling behaviors of the brushes were then thoroughly investigated as a function of grafting density and ionic strength using ellipsometry. A theoretical mean-field approach was also developed to quantify the contributions of the ion osmotic and nonelectrostatic effects. Accordingly, it was both experimentally and theoretically demonstrated how fundamentally different swelling behaviors can exist depending on the relative contributions of ion osmotic and nonelectrostatic effects. This new insight reveals new opportunities for applications of polyelectrolyte brushes based on their tunable hydrophobicity and provides new ideas for fundamental investigations of these systems.

Antimicrobial PDMS Surfaces Prepared through Fast and Oxygen-Tolerant SI-SARA-ATRP, Using Na2SO3 as a Reducing Agent

“…No significant differences were found for DMAEMA C8, DMAEMA C10, or DMAEMA (CH 2 ) 2 OCH 3 for any polymerization time. The discrepancy among the different modifications in terms of polymerization time is ascribed to the varying chain assembly due to nonelectrostatic effects, as recently described . Furthermore, WCA hysteresis, which was also calculated and can be found in Figure S5, shows a general increase after modification, further confirming the abovementioned conclusions.…”

“…The discrepancy among the different modifications in terms of polymerization time is ascribed to the varying chain assembly due to nonelectrostatic effects, as recently described. 41 Furthermore, WCA hysteresis, which was also calculated and can be found in Figure S5, shows a general increase after modification, further confirming the abovementioned conclusions. The IR and generally lower receding contact angles confirm a clear change in the surface chemistry of the PDMS substrate and corroborate the facilitation of the grafting and quaternization of DMAEMA.…”

Specific Counterion Effects on the Swelling Behavior of Strong Polyelectrolyte Brushes

“…From our previous work, we noted that the relative contributions from ion osmotic pressure and nonelectrostatic interactions to the total brush swelling strongly depend on the hydrophilicity/hydrophobicity of the polyelectrolyte chains. 16 Thus, to test our hypothesis about how counterions with different ion properties can affect these two swelling mechanisms, we chose to study polyelectrolyte brushes with a moderate hydrophobic character. Specifically, we synthesized two poly[2-(1-butylimidazolium-3-yl)ethyl methacrylate] brushes with similar chain lengths but with different grafting densities using SI-ATRP (Figure 1).…”

“…To this end, a recently developed mean-field approach, which takes both ion osmotic and nonelectrostatic effects into account, is adopted (see further details in Supporting Information, S3). 16 Briefly, a pressure balance equation is established to obtain the equilibrium brush thickness: Here, the four terms in this equation represent the contributions of the ion osmotic effects, the second and third virial terms for the nonelectrostatic effects, and the chain elasticity, respectively. The parameters f, r, c s , a, σ, χ, and ν m are the charge fraction, relative thickness (brush thickness/chain contour length), salt concentration in the medium, size of the polymer segment, grafting density, Flory−Huggins parameter, and volume of each repeating unit, respectively.…”

“…To this end, the influence of nonelectrostatic effects becomes more significant with both increasing brush grafting density and increasing brush hydrophobicity. 16 Therefore, it is our key hypothesis that different specific counterion effects can dominate for brushes with different grafting densities (where the contributions from nonelectrostatic effects have different weights) and for a brush with a fixed grafting density depending on the scaling regime (where the contributions from ion pairing and contributions to nonelectrostatic effects will have different weights). To test this hypothesis, we investigated the specific ion effects for a polyelectrolyte brush that shows a significant contribution from both ion osmotic and nonelectrostatic effects and evaluated the specific ion effects with systematic variations in grafting density and ionic strength.…”