Extensional Flow Behavior of Methylcellulose Solutions Containing Fibrils

The extensional properties of semidilute aqueous methylcellulose (MC) solutions have been characterized. Pure aqueous MC solutions are shear-thinning liquids at room temperature. With the addition of 8 wt % NaCl, a fraction of MC self-assembles into long fibrils, which modify the rheological properties of the original MC solution. Capillary Breakup Extensional Rheometry (CaBER) was used to characterize salt-free and 8 wt % NaCl solutions of MC at room temperature. The salt-free solutions exhibit only power-law behavior whereas solutions with NaCl exhibit both power-law and elastic regimes. As MC concentration increases, the extensional relaxation time also increases strongly, from 0.04 s at 0.5 wt % to 4 s at 1 wt %. In addition, the apparent extensional viscosity rapidly increases as a function of increasing MC concentration, from 40 Pa·s at 0.5 wt % to 1300 Pa·s at 1 wt %. This behavior is attributed to the presence of fibrils in the MC solutions containing NaCl.