Critical slowing down in polymer dynamics near the coil-stretch transition in elongation flow.

We present experimental results on relaxation dynamics of lambda-DNA and T4 polymer molecules toward a steady state in elongation flow. Strong critical slowing down (similar to the well-known effect in continuous phase transitions) in polymer relaxation near the coil-stretch transition (CST) is quantitatively investigated and found to be in good accord with predictions. For polymers with a small number of Kuhn segments the maximum of the relaxation time vs the strain rate provides precise information about the location of the CST and serves as its criterion.

Statistics of tumbling of a single polymer molecule in shear flow.

We present experimental results on statistics of polymer orientation angles relative to the shear plane and tumbling times in shear flow with thermal noise. The strong deviation of the probability distribution functions (PDFs) of the orientation angles from Gaussian PDFs was observed in good accord with theory. A universal exponential PDF tail for the tumbling times and its predicted scaling with Wi (that is, the dimensionless shear rate normalized by the polymer relaxation time) are also tested experimentally against numerics. The scaling relations of PDF widths for both angles as a function of Wi are verified and compared with numerics.