Polyelectrolyte brush bilayers in weak interpenetration regime: Scaling theory and molecular dynamics simulations

Abstract

We employ molecular dynamics (MD) simulations and develop scaling theories to quantify the equilibrium behavior of polyelectrolyte (PE) brush bilayers (BBLs) in the weakly interpenetrated regime, which is characterized by d_{0}<d_{g}<2d_{0}, where d_{g} is the gap between the opposing plates where the PE brushes are grafted and d_{0} is the unperturbed height of a PE brush grafted at a single plate. Scaling predictions establish that, for the weakly interpenetrated osmotic PE BBLs δ∼N^{1/2}(2-d_{g}/d_{0})^{1/2} (where δ is the interpenetration length and N is the number of Kuhn segments in PE brush). MD simulations excellently recover this dependence of δ on N and the extent of interpenetration (quantified by d_{g}/d_{0}). These predictions, unlike the existing studies, establish a finite interpenetration for all values of d_{g}/d_{0} as long as d_{g}<2d_{0}. Finally, we quantify the monomer and counterion concentration distributions and point out that these two distributions may quantitatively deviate from each other at locations very close to the channel centerline, where the interpenetration-induced monomer concentration can be significantly low.

Densely Grafted Polyelectrolyte Brushes Trigger “Water-in-Salt”-like Scenarios and Ultraconfinement Effect

“…Understanding the detailed structure of the PE brushes and their responses to external stimuli (such as salt concentration and pH) is critical to achieving better control of all these applications as well as to gain fundamental insight into one of the most interesting polymer states (namely the ''brush''-like state). Motivated by these prospects, there have been several decades of theoretical, [18][19][20][21][22][23][24][25][26][27] simulation-based, [28][29][30][31][32][33][34][35][36][37] and experimental [38][39][40][41][42][43][44][45][46][47] research unraveling a myriad of information on the structure and properties of PE brushes. Several of these studies have been partly based on simulation models and frameworks developed for other PErelated systems such as PE gels, [48][49][50][51] PE solutions, [52][53][54] and PE nanofilms.…”

Lubrication in polymer-brush bilayers in the weak interpenetration regime: Molecular dynamics simulations and scaling theories

“…As we are studying a weakly interpenetrated polymer BBL, a part of the polymer molecule is in the interpenetrated domain while the other part is outside the interpenetrated domain. The part that is in the interpenetrated domain can be considered to be described as blob-encased segments [61,62]. Following Kreer and Balko [42], we can express the interaction energy per unit area for the interpenetrated semidilute polymer BBLs as:…”

“…Kreer in his recent review has nicely summarized several key findings of these papers [21]. Very recently we extended these calculations for a different compression * sidd@umd.edu regime [61,62]: we considered a weakly interpenetrated regime characterized by 1 < d g /d 0 < 2. We conducted MD simulations and scaling analyses to establish a completely different scaling behavior of the equilibrium configuration of the polymer and PE brushes in comparison to those witnessed for highly compressed regimes.…”

Polymer Brush Friction in Cylindrical Geometries

“…At higher compressions, opposing brushes can interdigitate [12,13], which can increase frictional stresses by several orders of magnitude [14]. In fact, interdigitation between brushes can be switched using asymmetric brushes [15] and this can be employed to control the friction between surfaces [16].Molecular simulations have been employed extensively to obtain a microscopic picture of polymer brush friction [17][18][19][20][21][22][23][24][25][26]. With help of these simulations, friction-velocity relations have been derived [27][28][29][30][31][32].…”

“…Molecular simulations have been employed extensively to obtain a microscopic picture of polymer brush friction [17][18][19][20][21][22][23][24][25][26]. With help of these simulations, friction-velocity relations have been derived [27][28][29][30][31][32].…”