Understanding the behavior of DNA at high shear rates is important for DNA handling (in syringes, for example) and for serving as a good proxy for studying the rheology of semiflexible polymer solutions. Dakhil et al. observed this process, extending the accessible shear rate for DNA by about three orders of magnitude.

At lower shear rates, the authors found the viscosity of the DNA solutions matches well with previously reported values. Developing a power law dependence on the shear rate, the viscosity function eventually plateaus, approaching that of the solvent. Meanwhile, and perhaps most surprisingly, according to author Andreas Wierschem, the normal stress differences show different plateaus.

Despite not seeing any apparent fragmentation of the DNA at high shear rates, the group noted the DNA begins to experience permanent shear-induced changes at around 30,000 s−1, about 30% of the maximum shear rate in the study.

To obtain these rheological measurements, the researchers placed DNA solutions diluted to the desired concentrations in rotational rheometers with shear rates ranging between about 10 to 100,000 s−1. Most rheometer cannot access the upper limit of this range, which is why this extensive systematic study remained a necessity.

Wierschem said these findings can eventually help develop scaling theories of the viscosity and normal stress difference behavior of DNA and other polymer solutions undergoing high shear rates. This can help optimize DNA processing to avoid overstretching, among other applications.

Source: “Buffered λ-DNA solutions at high shear rates,” by H. Dakhil, S. K. Basu, S. Steiner, Y. Gerlach, A. Soller, Sharadwata Pan, Natalie Germann, M. Leidenberger, B. Kappes, and A. Wierschem, Journal of Rheology (2021). The article can be accessed at https://doi.org/10.1122/8.0000136.