The viscosity of PAM polyacrylamide solution mainly reflects the internal frictional resistance caused by the flow or relative motion of liquid molecules. Internal friction resistance is related to polymer structure, solvent properties, solution concentration, temperature and pressure. What are the factors that affect the viscosity of PAM polyacrylamide solutions?
Temperature is a reflection of the strength of random thermal motion of molecules, and the motion of molecules must overcome interactions between molecules, as well as 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 vary with temperature. Changes in temperature have a significant effect on the viscosity of polymer solutions. The viscosity of PAM polyacrylamide solution decreased with increasing temperature. 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 more easily the network structure is destroyed, so the viscosity decreases.
The viscosity of the PAM polyacrylamide solution changes with the extension of the hydrolysis time. The hydrolysis time is short and the viscosity is very small, which may be because the polymer has not yet formed a network structure; because the hydrolysis time is too long, the viscosity decreases, and the long hydrolysis time is due to the pam powder. caused by the loosening of the structure in solution. Partially hydrolyzed polyacrylamide dissolves in water and decomposes into negatively charged macromolecules. Intermolecular electrostatic repulsion and anionic repulsion between different chains on the same molecule cause the molecules to stretch and entangle with each other in solution, which is why partially hydrolyzed polyacrylamide can significantly increase its solution viscosity.
The number of cationic groups in the molecular chain of polyacrylamide PAM powder is more than that of anionic groups, and the net charge is more. According to the principle of similar miscibility, the polymer has better water solubility and higher intrinsic viscosity. As the mineral content increases, the positive electrostatic charges are partially surrounded by anions, forming an ionic atmosphere, which combines with the surrounding positive electrostatic charges, and the properties and viscosity of the polymer solution decrease. Mineral concentrations continue to increase, and positive and negative ionic groups form combinations of intramolecular or intermolecular hydrogen bonds. At the same time, the added salt ions broke the bond between positive and negative ions by shielding the positive and negative charges, resulting in an increase in the solubility of the polymer in water. These two effects compete with each other, resulting in a higher salt concentration in the polymer solution and a lower viscosity.
The viscosity of PAM polyacrylamide solution increases with the molecular weight of the polymer, which is the result of intermolecular interactions 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. When the content is slightly higher, mechanical entanglement is sufficient to affect the viscosity. When the content is very low, the polymer solution can be regarded as a network structure, the main feature of which is formed by the mechanical entanglement between chains and hydrogen bonds.
In general, it contains a small amount of water when dry and absorbs moisture from the environment quickly when dry. The homopolymer isolated by freeze drying method is a white soft amorphous solid. However, when precipitated out of solution and dried, it is a glassy partially transparent solid, and the dried polyacrylamide pam powder is a brittle white solid. Commercial polyacrylamide is usually dried under moderate conditions, and its moisture content is generally 5-15%. The polymer films prepared by casting on glass plates are transparent, hard and brittle solids. When the content is high, the solution contains many chain links in contact, which causes the polymer solution to gel. Therefore, the higher the relative molecular mass of the polymer, the easier it is to form chain entanglement.