The structure and intrinsic viscosity of the partially hydrolyzed polyacrylamide (HAPM) and polyacrylamide (PAM) in aqueous solution were investigated by comparative studies of molecular dynamics simulation over a wide range of the NaCl concentration. The radius of gyration (R(g)), the hydrodynamic radius (R(h)) and the ratio of the radius gyration and the hydrodynamic radius (ρ) were calculated for the PAM or HPAM in solutions with different NaCl concentrations at 298 K. The conformational changes of the polymer chain in different aqueous solution were discussed according to the molecular shapes. It was found that the change of the R(h) or the R(g) can reflect the change in the [η]. And the changes in the structure of the polymer chain with different NaCl concentrations were discussed via the ρ which can predict [η] changes. The results showed that behavior of the polymer solution calculated from the simulation agreed with the experimental measurements. Furthermore, the radial distribution functions for the HPAM solutions were investigated, which verified the micro-mechanism for the change of the structure. The results of this research showed that the computational method used in this work has practical applicability.

In our work, three kinds of functional monomers were selected to modify polyacrylamide (PAM) or partially hydrolyzed polyacrylamide (HPAM) by molecular dynamics simulation so as to achieve the stronger salt-tolerance of modified HM-HPAM. The radius of gyration (R (g)), the hydrodynamic radius (R (H)), the effective length (L (ef)) and the intrinsic viscosity ([η]) for modified PAM or HPAM were studied in aqueous solutions with different ionic strength at 298 K. The results showed that modified HM-HPAM has a stronger salt tolerance and the salt tolerance increases gradually from HM-HPAM1 to HM-HPAM3 because the monomers with different steric hindrance would reduce the curliness of molecular chains and, consequently, improve the salt tolerance. So, introducing the steric hindrance monomer into polymer will increase the salt tolerance of the polymer and it is indicated that the simulated results agree with the experimental results very well. Furthermore, the radial distribution function (RDF) has been used to investigate the effect of NaCl on the hydration of the -COO- groups of the HM-HPAM from microscopic view.

Weconstructedsolutionmodelscontaining differentamountsofwatermoleculeswithamassconcentrationofabout1g • mL-1 .Usingmoleculardynamics(MD) simulationswecalculatedtheradiusofgyration(R g)fornon鄄ionicPAM(PAM鄄H)andanionicPAM(HPAM)inpure waterandinaqueoussolutionswithdifferentmassfractionsofNaCl.Wediscussedtheirbehaviorsatdifferent temperatures.Wefoundthatthesalttoleranceofthepolyacrylamidesfromthesimulationagreedwiththeexperimental resultsatdifferenttemperatures.Furthermore,thesimulationresultsforallthesolutionmodelscontainingadifferent amountofwatermoleculesbasicallyshowedasimilartrend.Consideringcomputationalefficiency,thesolutionmodel containing2000watermoleculeswasselectedforourstudy.Theradialdistributionfunctions(RDF)fortheoxygenions andoxygenatomsoftheHPAMchainwereinvestigatedinNaClsolutionmodelcontaining2000watermolecules.The reducedviscosityofHPAMsolutionswithincreasingNaClmassfractionsandabetterthickeningabilityaswellas poorsalttolerancecomparedtoPAM鄄HwereexplainedconsideringtheirmicrostructuresasdeterminedbyRDF.