Polyelectrolyte
Polyelectrolytes are water-soluble compounds having a large chain length (polymers), anionic ( poly acids ) or cationic ( polybases ) carry dissociable groups.
The main agent of anionic polyelectrolytes ( polyanions ) are:
- Acrylamide copolymers
- Alginates
- Lignosulfonates
- Pectins
- Polyacrylic acids and the corresponding co- polymers
- Polyvinylsulfuric
- Polycarboxylic acids ( collective term )
- Polyphosphoric acids
- Polysaccharides
- Polystyrene sulfonate
The cationic polyelectrolyte are counted:
- Phenols
- Poly- diallyldimethylammonium chloride
- Polyethyleneimine
- Polyvinylamine
- Polyvinylpyridine
- Polyvinylammonium chloride
One can distinguish between strong polyelectrolytes that carry a permanent, independent of the pH of the solution charge, and weak polyelectrolyte whose dissociation depends on the pH value of the solution differ. Examples of strong polyelectrolytes are sodium polystyrene sulfonate (anionic ) or poly - diallyldimethylammonium chloride (cationic ), representatives of the weak polyelectrolytes polyacrylic acid ( sour) or polyethyleneimine ( basic). The properties of a polyelectrolyte solution are largely determined by the repulsive interactions between the like-charged groups on the polymer chain.
A typical example is the viscosity behavior of salt-free polyelectrolyte solutions. While the viscosity of neutral polymer solutions with increasing dilution decreases linearly polyelectrolyte show an increase in viscosity. This is explained with an increasing rigidity of the polymer by the repulsion of the like-charged groups, as in the case of concentration, the ionic strength of the solution decreases and thus the charges are shielded worse. This effect is known as polyelectrolyte. The charge intensity of polyelectrolytes can be determined accurately by titration ( polyelectrolyte ). The viscosity as a macroscopically accessible property of polymer solutions is thus determined by the conformation of the dissolved polyelectrolyte molecules. Strongly charged polyelectrolytes stretch prone to entanglement in the solution whereas polyelectrolytes with reduced charge or screened charges. This bunching can be in weak polyelectrolytes by the pH value and the salt concentration and at high polyelectrolyte exclusively controlled by the salt concentration. An important application of these properties is the polyelectrolyte adsorption on solid surfaces, as is the layer-by -layer method is used, for example. Dissolved polyelectrolytes can adsorb onto oppositely charged surfaces. The adsorption is, inter alia, driven by the electrostatic attraction between the charged and oppositely charged monomer dissociated surface groups (e.g., SiO groups to silicon dioxide surfaces ). But the release of counter-ions or the formation of hydrogen bonds allow adsorption. The conformation of the polyelectrolyte in the dissolved state determines the amount of substance adsorbed. Stretched polyelectrolyte molecules adsorb as thin films ( 0.2-1 nm ) on the surface whereas geknäulte polyelectrolyte thicker layers form (1-8 nm).
One belonging to the biopolymers, polyelectrolyte is strong and the DNA molecule.
Polyelectrolytes differ, in addition to their charge activity, especially with respect to their molar mass. Low molecular weight polyelectrolytes have a Molar mass up to 100,000 g · mol -1, high molecular weight polyelectrolytes to over 10 million. At a theoretical CC distance in the molecular chain of 1.53 angstroms, the molecular chain can attain a length of about 15 microns. Low molecular weight polyelectrolytes are primarily used as a dispersant, high molecular weight polyelectrolytes as flocculants. Molar mass as a function of the viscosity of the polyelectrolyte solutions increases. Low molecular weight solutions are watery to slightly viscous, high-molecular solutions already at a concentration of 0.1 % extremely viscous.
High molecular weight polyelectrolytes can not be produced because of the extreme viscosity of aqueous solutions, but only by bulk polymerization, using as end products powder arise, or by emulsion with liquid emulsions as end products.