For CB, the normalized retardance profiles overlap from 2 to 4 mg/mL and then decreases with increasing concentration. For CB/DMF, the specific retardance decreases throughout, from 2 to 10 mg/mL. The specific retardance for extensional flow of PII-2T in CB and CB/DMF is shown in Figure and D, respectively, where the curves largely overlap for all concentrations in both systems. Prior work on the flow birefringence of polymer solutions in extensional flow has shown that the birefringence increases linearly with concentration for dilute solutions ( ),