Shear and Extensional\nRheology of Cellulose/Ionic\nLiquid Solutions

Abstract

In this study, we characterize the shear and extensional\nrheology\nof dilute to semidilute solutions of cellulose in the ionic liquid\n1-ethyl-3-methylimidazolium acetate (EMIAc). In steady shear flow,\nthe semidilute solutions exhibit shear thinning, and the high-frequency\ncomplex modulus measured in small amplitude oscillatory shear flow\nexhibits the characteristic scaling expected for solutions of semiflexible\nchains. Flow curves of the steady shear viscosity plotted against\nshear rate closely follow the frequency dependence of the complex\nviscosity acquired using oscillatory shear, thus satisfying the empirical\nCox–Merz rule. We use capillary thinning rheometry (CaBER)\nto characterize the relaxation times and apparent extensional viscosities\nof the semidilute cellulose solutions in a uniaxial extensional flow\nthat mimics the dynamics encountered in the spin-line during fiber\nspinning processes. The apparent extensional viscosity and characteristic\nrelaxation times of the semidilute cellulose/EMIAc solutions increase\ndramatically as the solutions enter the entangled concentration regime\nat which fiber spinning becomes viable.