Relaxation dynamics and structural changes in DNA soft gels

Abstract

Abstract Herein, we report relaxation dynamics and structural changes occurring in DNA during transition of its solution to soft gel phase using data obtained from rheology, dynamic light scattering (DLS) and small angle neutron scattering (SANS) experiments. The viscoelastic response showed this transition taking place above a crossover concentration (CDNA = 2% (w/v)). It was observed that at low concentration CDNA = 1% (w/v) solution possessed multiple relaxation dynamics owing to the presence of internal modes at all temperatures in the range, T = 30–80 °C. At higher concentration (CDNA = 3% (w/v)) the system showed single relaxation dynamics because of the systematic arrest of many of these modes. However, at crossover concentration (CDNA = 2% (w/v)), samples showed multiple relaxation modes at high temperature (T = 80 °C) and single mode relaxation at lower temperature (T = 50 °C) with sub diffusive behaviour showing transition from ergodic to arrested phase owing to ceased Brownian dynamics. Normal diffusion in CDNA = 1% (w/v) and sub-diffusive behaviour for CDNA = 2% and 3% (w/v) samples was observed. SANS studies revealed interparticle distance decreased and mesh like structures began to appear with increase in DNA concentration, 2% ≤ CDNA ≤ 5% (w/v). Thus, the observed relaxation dynamics was hierarchical in DNA concentration and the same was temperature dependent. The results augment our general understanding of relaxation dynamics of DNA in aqueous dispersions.