Polyelectrolyte adsorption

The solution of these equations yields a simple relation for the adsorbed amount, Γ, based on electrolyte charge fraction, ρ, and bulk salt concentration,

Due to their unique nature, polyelectrolytes have many options for solvents that traditional polymers such as polyethylene, styrene, and others, would not be soluble in.

This is due to the screening the solvent molecules perform between the charged repeat units of the polyelectrolyte, decreasing the electrostatic repulsion the polymer chain experiences.

High salt concentrations cause conditions similar to the interactions experienced by a polymer in a favorable solvent.

Once this charge is screened the polyelectrolyte will act as any other non-polar polymer would in a high ionic strength solution and begin to minimize interactions with the solvent.

In a low ionic strength solution, the charges present on the repeat units of the polymer are the dominant force controlling conformation.

Since there is very little charge present to screen the repulsive interactions between the repeat units, the polymer assumes a very spread out, loose conformation.

Polyelectrolyte multi-layers are a promising area of research in the polymer coating industry because they can be applied in a spray-on fashion at low cost in a water-based solvent.

Although the polymers are held to the surface only by electrostatic forces, the multi-layer coatings adhere aggressively under liquid shear.

Polyelectrolytes have been used by scientists to coat stainless steel using the layer-by-layer application method in order to inhibit corrosion.

The exact mechanism by which corrosion is restricted is unknown because polyelectrolyte multi-layers are water-logged and of a gel-like consistency.

Additionally, the water molecules within the multi-layer film are held in a restricted state by the ionic groups of the polyelectrolytes.

The main mechanism of infection is the formation of a biofilm, which is a matrix of sessile bacteria consisting of around 15% bacterial cells by mass and 85% hydrophobic exopolysaccharide fibers.

This would be more effective than the current technique of releasing a high dose of drugs into the body and counting on some of it to navigate to the afflicted area.

The base layer for an effective coating for an implant is DMLPEI/PAA, or linear N, N-dodecyl,methyl-poly(ethyleneimine) / poly (acrylic acid).

[7] Another of the major applications of polyelectrolyte adsorption is the stabilization (or destabilization) of solid colloidal suspensions, or sols.

It can also be used to destabilize suspensions by adsorbing oppositely charged chains to the particle surface, neutralizing the zeta-potential and causing flocculation or coagulation of contaminants.

An application of the additional stability a polyelectrolyte multi-layer will grant a colloid is the creation of a solid coating for a liquid core.

A simple schematic showing the alternating adsorption of positively and negatively charged polyelectrolytes to a solid surface.
Representation of the effect of salt on a polyelectrolyte molecule in solution. Also, good solvents produce effects on polymers similar to the high salt condition and poor solvents produce effects similar to the low salt condition.
Precursor monomers for a base layer of a microbicidal implant-enhancing polyelectrolyte multi-layer. The top is DMLPEI, and bottom is PAA.
Top: The electrostatic contribution to colloid stability, showing two like-charged particles repelling each other. Bottom: The steric contribution to colloid stability, showing polymer chains opposing being pushed together and confined, causing a repulsion due to the unfavorable decrease in entropy.