摘要
A great progress has been made over the last decades in studying concentration scaling on rheometric properties of monodisperse polymer solutions.However,the effects of polydisperse polymer solutions on such a concentration scaling remain elusive.In this work,rheometric properties of industrially relevant polydisperse and high molecular weight polyacrylamide(PAAm)aqueous solution have been studied.The results show a concentration scaling of the characteristic relaxation time,the plateau modulus and the zero-shear viscosity across a concentration range from 10c^(*)to 250c^(*).The time-concentration superposition principle is validated and extended in the data analysis of the terminal dynamic regime.The concentration scaling exponent of their shifting factors is significantly smaller than the results of monodisperse polymer solutions in good andθsolvents reported in the literature.The steady shear viscosity and shear stress of 18M PAAm aqueous solutions with relatively lower concentration(≤35c^(*))could also be superimposed into a master curve with the shear-thinning exponent of 0.73±0.03 and0.27±0.03,respectively,over a wide range of shear rates in about six orders of magnitudes.However,for 18M PAAm aqueous solutions with higher concentration(≥48c^(*))in an intermediate shear thinning regime,the scaling exponent shows a pronounced concentration dependence.The shear thinning exponent of steady shear viscosity varies from 0.73 to 0.57 as concentration is increased,and then increases from 0.57 to 0.90from sufficiently high shear rate.Further increasing shear rate,the shear-thinning exponent of 18M PAAm aqueous solutions at all concentrations converges to the lower bounded value observed in the relatively less concentrated(≤35c^(*))18M PAAm aqueous solutions,i.e.,0.73±0.02 for shear viscosity and 0.27±0.02 for steady shear stress,respectively.It reveals that the concentration effects of polydisperse polymer solutions could be greatly reduced by the dynamic"molecular individualism”in strong shear flow.
基金
financially supported by the Ministry of Science and Technology of the People’s Republic of China(No.2020AAA0104804)。
