Synopsis Entangled DNA solutions are ideal as a model system to examine nonlinear shear flow behavior. Even when the number of entanglements per chain, Z, is higher than 100, the solution is still soft enough with an elastic plateau modulus under 100 Pa and is thus amenable to experimental study by commercial rotational rheometry without ambiguity and uncertainty. We have investigated nonlinear flow behavior of three entangled DNA solutions with Z = 24, 60, and 156, respectively, using a

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... tion of particle-tracking velocimetric ͑PTV͒ and conventional rheometric measurements. We explore questions such as ͑a͒ whether shear banding also occurs in moderately entangled solutions, ͑b͒ whether creep results in development of nonlinear velocity profile, ͑c͒ whether shear banding produced in startup shear and creep persists at long times in steady state, and ͑d͒ whether these entangled solutions exhibit homogeneous shear at the upper end of the stress plateau region. We found that the first DNA solution ͑Z =24͒ only shows transient weakly inhomogeneous shear and steady linear velocity profile. In the more entangled solutions ͑Z = 60 and 156͒, shear banding is observed in startup rate-and stress-controlled shear in the shear thinning regime. Shear homogeneity eventually returns at the upper end of the stress plateau ͑shear thinning͒ regime.