Poisson-Boltzmann theory of polyelectrolyte brushes
Oleg Borisov, IPREM, Université de Pau
The polyelectrolyte brush results if long flexible ionic polymer chains are attached by one end onto an impermeable solid surface or onto the surface of a colloidal particle and immersed in a solvent.
Understanding of the structure-properties relation in polymer and polyelectrolyte brushes is important for their applications for surface modification, in particular, in the field of biomaterial engineering. Functional polymer brush-like structures are found in biological systems. Examples of natural biopolyelectrolyte brushes include extracellular polysaccharides on bacterial surfaces, neurofilaments and microtubules with associated proteins, aggrecan macromolecules in articular cartilage, casein micelles etc. The possibility to trigger conformational transitions in surface-attached polymeric layers by external physical (temperature, electrical voltage, etc.) or chemical (pH, salinity, solvent composition, etc.) fields opens a perspective for design of stimuli-responsive interfaces.
Theory of equilibrium structural properties of polyelectrolyte brushes is developed in the frame of self-consistent field Poisson-Boltzmann approximation. We analyze the influence of ionic strength and (in the case of weak polyacid or polybase brushes) pH in the solution on the chain conformations in the brush. The effect of the counterion localization in the polyelectrolyte brush is most essential and governing the brush properties. The repulsive forces acting between surfaces or colloidal particles with grafted polyelectrolytes are calculated. Furthermore, we discuss interaction of polyelectrolyte brushes with multivalent counterions and with globular proteins and the effect of their accumulation in the brushes.