The Thickening Mechanism Study Of Polyacrylamide As Water Shutoff/profile Modification Agent

Polyacrylamide(PAM) applied to various fields is an important class of linear water-soluble polymers.Therefore, it is of great significance to study the solution properties of PAM. Experimental method does not reveal the full information of the solution properties of PAM. Hence, the theoretical guidance of research for viscosity of solutions mechanism is in urgent need. In recent years,with the denelopment of computer molecular simulation technology,the technology has been used to study the nature of the polymer solution and more research results were obtained.In this paper,we used molecular dynamic simulation and experimental methods to investigate the changing viscosity of partially hydrolyzed PAM aqueous solution under the different temperature,the different type of salts and the concentration of salt and found the microscopic mechanism.Through the reseach of HPAM,we confirmed that the moleular dynamic(MD) simulation can be used to study the PAM reliably.Then we reseached the amphoteric polyacrylamide(ACPAM) aqueous solution using MD simulation.We measure the viscosity of HPAM aqueous solution at different temperature,with different type of salts and different concentration salt.The viscosity of polymer solution reduced with the temperature increase.When we added the same concentration of NaCl,CaCl2,MgCl2,the viscosity of solution reduced.What’s more,the viscosity of solution decrease with the high concentration of NaCl.The polymer chains untwist in the high temperature solution,and decrease the flow resistance of the solution.When multivalent ions are added to the solution,the strong electrostatic attraction between ions and charged monomers favors condensation of the ions on the polymer backbone.At high NaCl concentration,salt ions can form layered structure around the polymer chain and locally overcompensate the effective polymeric charge.This overcompensate of the polymer charge leads to the chain swlling and the viscosity of solution decreasing.We used molecular dynamic simulation to investigate the changing viscosity of ACPAM aqueous solution under the different temperature,the different type of salts and the concentration of salt and found the microscopic mechanism.The viscosity of ACPAM aqueous solution decreased with the temperature increasing.The untwisting of the polymer chains contributed to this result.In salt solution chain size is very sensitive to the external perturbations.We found the ACPAM chain is shrinking in the NaCl,CaCl2,MgCl2 salt solution gradually.Then the configuration of ACPAM transformed in high NaCl concentration solution.This is a result of the screening of the intrachain electrcstatic interactions with increasing salt concentration.We extracted the radius of gyration and end-to-end distance of polymer chain and the radial distribution function of atoms of system and interaction energy to search the microscopic mechanism of polymer solution.