Early Onset of Non-Linear Response in Entangled Monodisperse DNA Solutions*

It is generally observed that entangled polymer melts and solutions exhibit linear rheological response for the dynamic moduli [G'(ω) and G''(ω)] to shear strains of the order of 50 to 100%.  We recently[1] discovered that λ-phage DNA, a double-stranded linear DNA having a molecular weight of 48.5 kbp (3.1x10⁷ g/mol), that this ideally monodisperse system did not behave in the same way as do synthetic polymers.  Rather the onset of non-linear rheological behavior is seen at strains of approximately 2% or less depending on frequency of the oscillatory shear.  Furthermore, unlike the synthetic polymers, the λ-DNA solutions exhibit an onset of non-linearity that occurs at decreasing strains as the frequency of test decreases. Importantly, non-monodisperse DNA solutions, such as calf-thymus DNA have been reported to exhibit behavior similar to linear polymers[2]. The reasons for this are not currently understood and lead to fundamental questions about the rheology of entangled systems.  Is DNA fundamentally different from the linear synthetic counterpart? or does polydispersity lead to a different behavior?

[1] S. Banik, D. Kong, M.J. San Francisco, and G. B. McKenna, Macromolecules, 2021, 54, 8632−8654.

[2]  T.G. Mason, A. Dhople and D. Wirtz, Macromolecules 1998, 31, 3600-3603.