What are the factors that affect the viscosity of polyacrylamide?

The viscosity of polyacrylamide solution mainly reflects the internal friction resistance caused by flow or relative movement between liquid molecules. Internal friction resistance is related to factors such as the structure of the polymer, the nature of the solvent, the concentration of the solution, temperature and pressure. The larger its value, the greater the viscosity of the solution. So what are the factors that affect the viscosity of polyacrylamide?
1. Effect of temperature on viscosity of polyacrylamide
Temperature is a reflection of the intensity of the irregular thermal motion of molecules. The movement of molecules must overcome the interaction force between molecules, and the interactions between molecules, such as intermolecular hydrogen bonds, internal friction, diffusion, molecular chain orientation, entanglement, etc., Directly affects the viscosity, so the viscosity of the polymer solution will change with temperature. The effect of temperature changes on the viscosity of polymer solutions is significant. The viscosity of the polyacrylamide solution decreases as the temperature increases. The reason is that the dispersed phase particles of the polymer solution are entangled with each other to form a polymer with a network structure. The higher the temperature, the easier it is to destroy the network structure, so the viscosity decreases. .
2. Effect of hydrolysis time on viscosity of polyacrylamide
The viscosity of polyacrylamide solution changes with the extension of hydrolysis time. Short hydrolysis time results in smaller viscosity, which may be due to the fact that the polymer has not had time to form a network structure. If hydrolysis time is too long, the viscosity decreases, which is the reason for polyacrylamide Caused by the loosening of the structure in solution. Partially hydrolyzed polyacrylamide dissociates into negatively charged macromolecules after being dissolved in water. The electrostatic repulsion between molecules and the anionic repulsion between different links on the same molecule cause the molecules to stretch in the solution and make the molecules entangle with each other. , which is why partially hydrolyzing polyacrylamide can significantly increase the viscosity of its solution.
3. Effect of salinity on viscosity of polyacrylamide
There are more cationic groups in the polyacrylamide molecular chain than anionic groups, more net charge, and greater polarity. H20 is a polar molecule. According to the principle of similar miscibility, the polymer has better water solubility and intrinsic viscosity. Larger; as the mineral content increases, the positive electrostatic charge is partially surrounded by anions to form an ionic atmosphere, which combines with the surrounding positive electrostatic charges. The polarity and viscosity of the polymer solution decreases; the mineral concentration continues to increase, The positive and negative ion groups form an intramolecular or intermolecular hydrogen bond association (leading to a decrease in the solubility of the polymer in water). At the same time, the added salt ions shield the positive and negative charges and break up the association between the positive and negative ions. The formed salt bonds are destroyed (leading to an increase in the solubility of the polymer in water), and these two effects compete with each other so that the viscosity of the polymer solution remains small at higher salt concentrations (>0.06 mol/L).
4. Effect of molecular weight on viscosity of polyacrylamide
The viscosity of polyacrylamide solution increases with the increase of polymer molecular weight. This is because the viscosity of polymer solution is generated by the interaction between molecules during molecular motion. When the relative molecular mass of the polymer is about 106, the polymer coils begin to penetrate each other, which is enough to affect the scattering of light. At slightly higher levels mechanical entanglement is sufficient to affect viscosity. At fairly low levels, the polymer solution can be viewed as a network structure, with mechanical entanglements between chains and hydrogen bonds forming the nodes of the network. When the content is higher, the solution contains many chain-chain contact points, making the polymer solution gel-like. Therefore, the greater the relative molecular mass of the polymer, the easier it is for chain entanglements to form between molecules, and the greater the viscosity of the solution.