Supramolecular Organization in Calf-Thymus DNA Solutions under Flow in Dependence with DNA Concentration

DNA dynamics and flow-properties are of great importance for understanding its functions. DNA is a semiflexible polymer chain characterized by having-a large persistence length of around 50 nm and high charge density; DNA chains are interacting efficiently at high concentrations, in dependence of the ionic concentration. In relation with DNA molecular characteristics, it is also known-that DNA solutions are able to form liquid crystalline phases over a critical polymer concentration: In this work, the supramolecular organization in,calf-thymus DNA solution, with low degree of entanglement, appearing under flow-was studied in a wide DNA concentration range from 2 to 10 mg/mL, at a pH of 7.3 and 20 degrees C. The rheological behavior of the system was studied using steady state flow and oscillatory measurements. Transient regimes were also tested by imposing controlled shear rates, on a short time up to steady state. Furthermore, a combination of visual observations and flow birefringence measurements. was proposed to reach a better understanding of the obtained theological behavior. The presence of a shear-induced texture is revealed under flow for the calf-thymus DNA solutions at C-DNA> 5 mg/mL and attributed to organized domains of DNA molecules, named in the text as crystalline parts, which are progressively oriented under shear. Finally, at high shear rates (over 100 s(-1)), it is shown that for the DNA solutions the orientation of these organized DNA domains and connecting chains under flow goes to an anisotropic monodomain.