The Extensional Rheology of Semi- Dilute Dna Solutions

The rheological behaviour of polymer melts and dilute polymer solutions in elongational flow have been extensively examined through experiments and theoretical predictions. However, an experimental study to understand the extensional rheological properties of polymer solutions in the semi-dilute regime is currently lacking in terms of a systematic examination of the effects of concentration and molecular weight. Previous experiments have demonstrated that significant viscoelastic effects characterize the rheological behaviour of semi-dilute polymer solutions in shear flows. It is anticipated that these effects will be even more pronounced in extensional flows, which play a critical role in a number of industrial contexts such as fibre spinning and ink-jet printing. In this work, the extensional rheology of linear DNA molecules in a wide range of molecular weights (25 – 289 kilobasepairs) and concentrations has been investigated. DNA solutions are now routinely used as model polymeric systems due to their near-perfect monodispersity. A filament stretching rheometer has been used since it is the most reliable method for obtaining an estimate of the elongational stress growth of a polymer solution. Steady-state uniaxial extensional viscosities of DNA dissolved in a viscous solvent under excess salt conditions have been determined in the semi-dilute regime at room temperature. The dependence of the steady state uniaxial extensional viscosities on concentration is observed to display universal behaviour, which can be validated by theoretical predictions. The material functions obtained in this work will provide benchmark data that are useful for the characterization of these industrially important systems.