Polyelectrolyte Desorption and Exchange Dynamics near the Sharp Adsorption Transition:  Weakly Charged Chains

Abstract

This paper examines the desorption and self-exchange dynamics of polyelectrolyte chains on an oppositely charged surface, in the limit of weak charge, such that the polymer is readily displaced by added ions. The model system adhering to this physically limiting behavior is poly[(dimethylamino)ethyl methacrylate] [PDMAEMA] adsorbing on silica from aqueous solution at elevated pH. Desorption kinetics follow expectations: a single-exponential decay consistent with a first-order desorption model, with an activation energy for chain removal that adheres reasonably to the Muthukumar treatment and quantitatively to the Dobrynin−Rubinstein model. Self-exchange kinetics, however, present a surprise: They are quantitatively identical to desorption, with the exchange process being completely controlled by chain release from the surface. The single-exponential form for self-exchange is atypical, and the quantitative similarity with desorption suggests that, with weakly charged chains, approximately 3−5 segment−surface contacts make up a minimum dynamic unit for adhesion.

The impact of nanoscale chemical features on micron-scale adhesion: Crossover from heterogeneity-dominated to mean-field behavior

“…This corresponds to 14-15 uncompensated positive charges per patch) [66,69]. We have also confirmed that the adsorbed patches are not displaced or transferred during these experiments, nor do they exhibit any lateral mobility [70].…”

“…At this ionic strength for deposition, the Debye length is sufficiently small so that the chains are random coils. Based on a lack of mobility at the conditions of study, we expect that variations in ionic strength during particle capture did not facilitate rearrangements of the adsorbed polymer coils [70,77]. Also, at these deposition conditions, the transport-limited deposition rate has been well-studied by optical reflectometry, so precise timing during the adsorption produces tight (±0.005 mg/m 2 ) control over the density of polymer deposited [65,66].…”

Adsorption of cationic polymers on the surfaces of anionic glass microspheres

“…Coatings stable in a wide range of pH values, concentrations of salts and low molecular mass competitors, and temperatures are formed during the adsorption of ionogenic homopoly mers on oppositely charged surfaces with high charge densities [24][25][26]. As the content of ionogenic groups in the polymer is decreased, the stability of the poly mer coating in water-salt solutions becomes lower: Desorption of the polymer occurs at lower salt con centrations in the surrounding solution [27,28]. A similar picture was observed in [29], in which a reduction in the effective charge of a weak polyelectro lyte macromolecule was attained through a change in the solution pH.…”

Selective adhesive cell capture without molecular specificity: new surfaces exploiting nanoscopic polycationic features as discrete adhesive units

“…Due to the strong electrostatic attractions between the polycation and the negative silica surface, the pDMAEMA is immobilized on the timescales and conditions in this study. 62, 63 …”