Abstract
In this study, the model framework that includes almost all relevant parameters of interest has been developed to quantify the electrostatic potential and charge density occurring in microchannels grafted with polyelectrolyte brushes and simultaneously filled with polyelectrolyte dispersion. The brush layer is described by the Alexander-de Gennes model incorporated with the monomer distribution function accompanying the quadratic decay. Each ion concentration due to mobile charges in the bulk and fixed charges in the brush layer can be determined by multi-species ion balance. We solved 2-dimensional Poisson–Nernst–Planck equations adopted for simulating electric field with ion transport in the soft channel, by considering anionic polyelectrolyte of polyacrylic acid (PAA). Remarkable results were obtained regarding the brush height, ionization, electrostatic potential, and charge density profiles with conditions of brush, dispersion, and solution pH. The Donnan potential in the brush channel shows several times higher than the surface potential in the bare channel, whereas it becomes lower with increasing PAA concentration. Our framework is fruitful to provide comparative information regarding electrostatic interaction properties, serving as an important bridge between modeling and experiments, and is possible to couple with governing equations for flow field.
Highlights
Polymer brushes are widely used to control the physical and chemical properties of solid surfaces, according to changes of molecular structure and chemical composition [1,2,3].The reconstruction of bulk polymers results in long response times, since various polymer constituents either migrate to the surface from the bulk or rearrange locally
The prototype channel is considered as polydimethylsiloxane (PDMS) surface grafted with anionic polyacrylic acid (PAA) brush
The channel length is much larger than its width and height, so that the variations of electrostatic potential and charge larger than its width and height, so that the variations of electrostatic potential and charge density are neglected along the direction of channel length
Summary
Polymer brushes are widely used to control the physical and chemical properties of solid surfaces, according to changes of molecular structure and chemical composition [1,2,3]. The prototype channel is considered as polydimethylsiloxane (PDMS) surface grafted with anionic polyacrylic acid (PAA) brush Both electrostatic potential and charge density with the swelling (i.e., the ratio of the radius of gyration of the perturbed chain to that of the θ-state) of PAA are numerically computed from the PNP continuum model according to variations of solution pH. These data provide useful information to experimental scientists because direct measurements are not possible.
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