Electrochemically Active Polyelectrolyte-Modified Electrodes

MARIO TAGLIAZUCCI; ERNESTO J. CALVO

Chemically Modified Electrodes

Wiley VCH

Lugar: Weinheim, Alemania; Año: 2009; p. 57 - 116

A polyelectrolyte solution contains the salt of a polyion, a polymer comprised of repeating ionized units. In dilute solutions, a substantial fraction of sodium ions are bound to polyacrylate at concentrations where sodium acetate exhibits only dissociated ions. Thus counter ion binding plays a central role in polyelectrolyte solutions.[1] Close approach of counter ions to polyions results in mutual perturbation of the hydration layers and the description of the electrical potential around polyions is different to both the Debye-Huckel treatment for soluble ions and the Gouy-Chapman model for a surface charge distribution, with Manning condensation of ions around the polyelectrolyte. Coulombic, van der Waals, entropic and osmotic forces are coupled in a non trivial way and give rise to important charge regulation in polyelectrolyte systems. The salt concentration is also an important factor to define the structure and thermodynamic properties of polyelectrolyte solutions. In weak poly-electrolytes the ionization equilibrium is also coupled to these interactions and thus the pK of ionizable groups depends on the organization of the interface and differs from that for the isolated molecule. Polyelectrolyte complexes formed by polyion pairing are of special interest, including protein-polyelectrolyte interactions such as protein-DNA complexes. A special case of polyelectrolyte complexes are polyelectrolyte multilayers (PEM) on surfaces formed by ion pairing, van der Waals interactions and counter ion release of oppositely charged polyelectrolytes.[2, 3] In this chapter we describe the use of polyelectrolytes carrying redox active centers on electrode surfaces with particular emphasis on organized layer-by-layer redox polyelectrolyte multilayers (RPEM). In redox active polyelectrolyte multilayers the polyion-polyion intrinsic charge compensation can be broken by ion exchange driven by the electrochemical oxidation and reduction forming extrinsic polyion-counter ion pairing. In this chapter we describe the structure, dynamics and applications of these systems.