Using retardance imaging, we first compare the polymer solution state response to shear and extensional flow. Solutions of PII-2T in CB at 10 mg/ml were flowed through the microchannels to measure flow-induced retardance resulting from the shear and extensional strain rate. Figures and depict the expected strain rate in the microchannels, which corresponds to the magnitude of the rate-of-strain tensor, | | √ , as calculated using COMSOL. The maximum shear and extensional strain rate occur at the walls and at the stagnation point, respectively, where the retardance is measured. Experimental retardance imaging throughout the channel is shown for several different strain rates for the narrow (shear)