What is the Difference Between Anionic and Cationic Polyelectrolytes

A polyelectrolyte is a large molecule with repeating units that carry an electrical charge. They can be categorized into two groups as a anionic and cationic polyelectrolytes based on the type of charge they carry.

What is the difference between anionic and cationic polyelectrolytes? Anionic polyelectrolytes carry a negative charge whereas cationic polyelectrolytes carry a positive charge.

Key Areas Covered

1. What are Anionic Polyelectrolytes 
      – Definition, Features 
2. What are Cationic Polyelectrolytes 
      – Definition, Features 
3. Similarities Between Anionic and Cationic Polyelectrolytes
      – Outline of Common Features
4. Difference Between Anionic and Cationic Polyelectrolytes 
      – Comparison of Key Differences
5. FAQ: Anionic and Cationic Polyelectrolytes
      – Answers to Frequently Asked Questions

Key Terms

Anionic Polyelectrolytes, Cationic Polyelectrolytes

What are Anionic Polyelectrolytes

Anionic polyelectrolytes are polymers that carry a negative charge. These are large molecules consisting of repeating units. These units contain functional groups that contribute to the negative charge. Frequently found functional groups in these molecules include carboxyl (-COOH) and sulfonic acid (-SO3H) groups. These groups dissociate in water to release hydrogen ions (H+), leaving behind a negatively charged molecule. Due to the presence of ionic charge, they are generally soluble in water.

There are many applications of anionic polyelectrolytes across various industries. In water treatments, it is used for flocculation, dewatering and scale inhibition. In paper industry, it improves paper strength and drainage. Moreover, in oil and gas industry, it is used in drilling fluids and for enhanced oil recovery. Anionic polyelectrolytes are also useful in textile industry, especially in dyeing and finishing processes.

What are Cationic Polyelectrolytes

Cationic polyelectrolytes are polymers that have a net positive charge. This is due to the presence of positively charged functional groups present in the molecules. These polymers are typically large, chain-like molecules composed of repeating units.

The commonly found functional groups in the molecule includes amine (-NH2) and quaternary ammonium (-NR4+) groups. These groups have the ability to accept a proton (H+), resulting in a positively charged species. The degree of ionization of these functional groups is determined by the pH of the solution. The effectiveness also cationic polyelectrolytes depend on the temperature and presence of other ions in the solution.

Cationic polyelectrolytes have a strong affinity for negatively charged surfaces and particles. This is due to their positive charged nature. Due to this property, these are found in a variety of applications. In water treatment, they are used to remove the suspended solids and colloidal particles from water. Here, they neutralize these particles present in the water. These polymers can also improve the dewatering properties of sludge.

Cationic polyelectrolytes can be used to enhance the separation of oil and water emulsions. In paper industry, it is used in retention and drainage and sizing. In wastewater treatment, they are used to remove the suspended solids, odor control, and in nutrient removal.

Similarities Between Anionic and Cationic Polyelectrolytes

1. Both are polymers, consisting of long chains of repeating units.
2. Due to their ionic nature, both types tend to be water-soluble.
3. Both exhibit polyelectrolyte behavior.
4. Both are used in water treatment processes.

Difference Between Anionic and Cationic Polyelectrolytes

Definition

• Anionic polyelectrolytes are polymers that carry a negative charge while cationic polyelectrolytes are polymers that carry a positive charge.

Groups

• Anionic polyelectrolytes typically contain carboxyl (-COOH) or sulfonic acid (-SO3H) groups, while cationic polyelectrolytes usually contain amine (-NH2) or quaternary ammonium (-NR4+) groups.

Particles

• Anionic polyelectrolytes interact with positively charged particles, while cationic polyelectrolytes interact with negatively charged particles.

Neutralization

• While anionic polyelectrolytes neutralize positively charged particles, cationic polyelectrolytes neutralize negatively charged particles.

Use

• Anionic polyelectrolytes are often used for flocculation, dewatering, and scale inhibition, whereas cationic polyelectrolytes are commonly used for coagulation, flocculation, and disinfection.

Conformation

• Anionic polyelectrolytes tend to have a more compact or coiled conformation in solution, but cationic polyelectrolytes often exhibit an extended or stretched conformation in solution.

FAQ: Anionic and Cationic Polyelectrolytes

1. What is a polyelectrolyte?

A polyelectrolyte is a large molecule with repeating units that carry an electrical charge. When dissolved in water, these charges dissociate, giving the molecule unique properties similar to both salts and polymers.

2. What are the different types of polyelectrolytes?

Polyelectrolytes are polymers with charged groups. They can be natural (like pectin, alginate), synthetic (like polyacrylic acid), or modified natural. They can carry positive (cationic), negative (anionic) charges, or both (ampholytic).

3. What is the difference between cationic and anionic polymer wastewater?

Cationic polymers have a positive charge, attracting negatively charged particles in wastewater, while anionic polymers have a negative charge, attracting positively charged particles.

4. What is the difference between anionic and cationic coagulants?

Anionic coagulants have a negative charge, attracting positively charged particles. Cationic coagulants, on the other hand, have a positive charge, attracting negatively charged particles.

5. What is another name for a polyelectrolyte?

Polysalt is another term for a polyelectrolyte. These large molecules possess both properties of electrolytes (due to their charged groups) and polymers (long chains).

Reference:

1. “Polyelectrolyte.” Science Direct.

Image Courtesy:

1. “Polyelectrolyte Examples” By Kebes at en.wikipedia – Transferred from en.wikipedia by Ronhjones (Public Domain) via Commons Wikimedia