Polyacrylamide (PAM) is a polymer commonly used in various industrial and environmental applications. It can exist in different ionic states based on the type of ions associated with the polymer backbone. The two main forms of polyacrylamide based on ionic charge are anionic polyacrylamide (APAM) and cationic polyacrylamide (CPAM). Here are the key differences between the two:

1. Ionic Charge:

   - APAM: Anionic polyacrylamide carries a negative charge on its polymer backbone due to the presence of anionic functional groups, such as carboxylate (-COO-) or sulfonate (-SO3-) groups. These groups dissociate in water, resulting in negatively charged polymer chains.

   - CPAM: Cationic polyacrylamide possesses a positive charge on its polymer backbone due to the presence of cationic functional groups, such as amino (-NH2) or quaternary ammonium groups (-N+(CH3)3). These groups dissociate in water, resulting in positively charged polymer chains.

2. Applications:

   - APAM: Anionic polyacrylamide is primarily used in applications where flocculation, clarification, and sedimentation of negatively charged particles or suspended solids are required. It is commonly utilized in wastewater treatment, sludge dewatering, mining, and oil field applications.

   - CPAM: Cationic polyacrylamide is used when flocculation and solid-liquid separation of positively charged particles or suspended solids are necessary. It is often employed in industries like papermaking, textile, water treatment, and as a retention aid in paper manufacturing.

3. Flocculation Mechanism:

   - APAM: Anionic polyacrylamide interacts with the negatively charged particles or colloids in the suspension through electrostatic attraction. The negative charges on the APAM polymer chains attract and neutralize the particles, resulting in the formation of larger flocs and aiding in their sedimentation or removal.

   - CPAM: Cationic polyacrylamide interacts with the positively charged particles or colloids in the suspension through electrostatic attraction. The positive charges on the CPAM polymer chains attract and neutralize the particles, leading to the formation of larger flocs and facilitating their settling or separation.

4. Efficiency in Different pH Ranges:

   - APAM: Anionic polyacrylamide is more effective in neutral to alkaline pH ranges (pH 6-10), where the negative charge on the polymer remains stable.

   - CPAM: Cationic polyacrylamide is more efficient in acidic to neutral pH ranges (pH 4-8), where the positive charge on the polymer remains stable.

It's important to note that there are also non-ionic polyacrylamides that carry no ionic charge. These non-ionic PAMs are often used for applications such as lubrication, friction reduction, and enhanced recovery.