Polyelectrolytes combine the properties of electrolytes (salts) and polymers (high MW compounds). For this reason they have sometimes been called polysalts. Like salts, their solutions are electrically conductive. Like polymers, their solutions are often viscous. Polyelectrolytes are used in numerous applications including water treatment, cosmetics and foods. Some of the polyelectrolytes that appear on food labels are pectin, carageenan, alginates and carboxymethylcellulose. All but the last are of natural origin.
They are distinct in structure and property from the broad class of electrolytes (i.e. salts). An electrolyte is a substance which dissociates free ions when dissolved (or molten), to produce an electrically conductive medium. ...
Polyelectrolytes also enable the growth of thin polymer films through what is known as layer-by-layer (LbL) deposition. During LbL deposition, a suitable growth substrate is dipped back and forth between dilute baths of positively and negatively charged polyelectrolyte solutions. During each dip a small amount of polyelectrolyte is adsorbed and the surface charge is reversed, allowing the gradual and controlled build-up of electronically stitched films of polycation-polyanion layers. Scientists have demonstrated thickness control of such films down to the single-nanometer scale. LbL films can also be constructed by substituting charged species such as nanoparticles or clay platelets in place of or in addition to one of the polyelectrolytes. LbL deposition has also been accomplished using hydrogen bonding.
The main benefits to LbL coatings involve the ability to conformably coat objects, the environmental benefits of using water-based processes, reasonable costs, and the utilization of the particular chemical properties of the film for further modification, such as the synthesis of metal or semiconductor nanoparticles, or porosity phase transitions to create anti-reflection coatings, optical shutters, and superhydrophobic coatings.
External Links
Polyelectrolytes, Department of Polymer Science, University of Southern Mississippi (http://www.psrc.usm.edu/macrog/electro.htm)
The microchannel device of claim 11, wherein an outermost layer of said polyelectrolyte layers disposed on a first portion of said microchannel surface of one said arm is negatively charged and an outermost layer of said polyelectrolyte layers disposed on a second portion of said microchannel surface of said one arm is positively charged.
A polyelectrolyte layer is disposed as an outermost surface on the first microchannel wall portion and a second polyelectrolyte layer of opposite charge is exposed as an outermost surface on the second microchannel wall portion.
At least one polyelectrolyte layer is formed on selected surfaces of the microchannel by exposing a selected portion of a first microchannel wall surface and a selected portion of the second microchannel wall surface of the microchannel to a first solution comprising first charge polyelectrolytes.
Polyelectrolyte properties are thus similar to both electrolytes (salts) and polymers (high molecular weight compounds), and are sometimes called polysalts.
A 'weak' polyelectrolyte, by constrast, has a dissociation constant (pKa or pKb) in the range of ~2 to ~10, meaning that it will be partially dissociated at intermediate pH.
Although the statistical conformation of polyelectrolytes can be captured using variants of conventional polymer theory, it is in general quite computationally intensive to properly model polyelectrolyte chains, owing to the long-range nature of the Coulomb interaction.
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