The critical crosslinking concentration of linked polymer solutions(LPS) formed by low concentration and high molecular weight partially hydrolyzed polyacrylamide (HPAM) and aluminum citrate(AlCit) was investigated by using dynamic viscosimetry

nuclear pore membrane

dynamic light scattering and 27Al-NMR measurements．The experimental results show that the viscosity and spin-lattice relaxation time (T13) of HPAM／AlCit crosslinking systems decrease with reaction time in low concentrations(the concentration of HPAM is between 100 mg／L and 200 mg／L) and increase with reaction time in a high concentration (300 mg／L)．The results measured by dynamic light scattering show that the mean hydrodynamic radius of linked polymer coils(LPC) is about 238 nm and 246 nm with HPAM concentrations of 100 mg／L and 200 mg/L in the solution．respectively．The filtration velocity of the LPS with HPAM concentrations of 100 mg/L and 200 mg／L in the solution is almost the same．The mean hydrodynamic radius of LPC is about 379 nm in the LPS with HPAM concentrations of 300 mg／L

and the filtration velocity of the LPS is lowered obviously．These results indicate that the linked polymer solution is formed by intra-molecular crosslinking of HPAM and AlCit forming linked polymer coils in the system of lower concentration. When the polymer concentration of HPAM／AlCit system is increased to a critical concentration

the weak gel is formed by crosslinking of LPC．The critical crosslinking concentration of LPS is between 200 mg／L and 300 mg／L for the system made up of HPAM molecular weight 1.4 × 107 and NaCl concentration 2000 mg／L. The critical crosslinking concentrations of the linked polymer solution measured by different methods are consistent with each other．