Temperature is a reflection of the intensity of the irregular thermal movement of molecules. The movement of molecules must overcome the interaction between molecules, and the interaction between molecules, such as hydrogen bond, internal friction, diffusion, molecular chain orientation, entanglement, etc., directly affects the viscosity, so the viscosity of polymer solution will change with temperature. The effect of temperature change on the viscosity of polymer solution is significant. The viscosity of polyacrylamide solution decreases with the increase of temperature. The reason is that the dispersed phase particles of polymer solution entangle with each other to form polymer with network structure. The higher the temperature is, the more easily the network structure is destroyed, so the viscosity of polyacrylamide solution decreases.
The viscosity of polyacrylamide solution changes with the prolongation of hydrolysis time. The hydrolysis time is short and the viscosity is small, which may be due to the fact that the polymer does not have time to form a network structure; the hydrolysis time is too long and the viscosity decreases, which is due to the structure of Polyacrylamide in the solution is loose. After partially hydrolyzed polyacrylamide dissolves in water, it dissociates into macromolecules with negative charge. The electrostatic repulsion between molecules and the anionic repulsion force between different chains on the same molecule cause the molecules to stretch in the solution and intertwine with each other, which is the reason why partially hydrolyzed polyacrylamide can significantly increase the viscosity of the solution.
In the molecular chain of polyacrylamide, the number of cationic groups is more than that of anionic groups. The net charge is more, and the polarity is larger, while H20 is a polar molecule. According to the similar phase solubility principle, the polymer has better water solubility and higher intrinsic viscosity; with the increase of mineral content, the positive static charge part is surrounded by anions to form an ionosphere, so as to combine with the surrounding positive static charge and polymerize. The polarity of the solution decreases and the viscosity decreases; the mineral concentration continues to increase, and the positive and negative ion groups form intramolecular or intermolecular hydrogen bond association (resulting in the decrease of the solubility of the polymer in water). At the same time, the added salt ions break the formed salt bond (resulting in the increase of the solubility of the polymer in water) by shielding the positive and negative charges and breaking up the association between the positive and negative ions. The two kinds of interaction compete with each other, which makes the viscosity of polymer solution keep smaller at higher salt concentration (>0.06mol/L).
The viscosity of polyacrylamide solution increases with the increase of molecular weight of polymer, which is due to the interaction between molecules during the molecular movement. When the relative molecular weight of the polymer is about 106, the polymer threads begin to penetrate each other, which is enough to affect the light scattering. The mechanical tangle is enough to affect the viscosity when the content is a little higher. When the content is very low, the polymer solution can be regarded as a network structure, and the mechanical entanglement and hydrogen bond form the nodes of the network. When the content is high, the solution contains many chain link contacts, so that the polymer solution is gelatinous. Therefore, the higher the relative molecular weight of the polymer, the easier it is to form chain entanglement between the molecules, and the higher the viscosity of the solution.