Elastic turbulence in entangled semi-dilute DNA solutions measured with optical coherence tomography velocimetry

Abstract

The flow instabilities of solutions of high molecular weight DNA in the entangled semi-dilute concentration regime were investigated using optical coherence tomography velocimetry, a technique that provides high spatial (probe volumes of 3.4 pL) and temporal resolution (sub μs) information on the flow behaviour of complex fluids in a rheometer. The velocity profiles of the opaque DNA solutions (high and low salt) were measured as a function of the distance across the gap of a parallel plate rheometer, and their evolution over time was measured. At lower DNA concentrations and low shear rates, the velocity fluctuations were well described by Gaussian functions and the velocity gradient was uniform across the rheometer gap, which is expected for Newtonian flows. As the DNA concentration and shear rate were increased there was a stable wall slip regime followed by an evolving wall slip regime, which is finally followed by the onset of elastic turbulence. Strain localization (shear banding) is observed on the boundaries of the flows at intermediate shear rates, but decreases in the high shear elastic turbulence regime, where bulk strain localization occurs. A dynamic phase diagram for non-linear flow was created to describe the different behaviours.

Single polymer dynamics for molecular rheology

“…Here, it was found that only high levels of entanglement (Z [214]. Finally, recent methods in optical coherence tomography and velocimetry measurements have further confirmed the existence of shear banded flow profiles in highly entangled DNA solutions [215].…”

Rheological and Flocculation Analysis of Microfibrillated Cellulose Suspension Using Optical Coherence Tomography

“…Furthermore, DOCT appears capable of very accurate measurement of velocity profile very close to a channel wall [18]. Due to the high sampling rate (which varies from tens to some hundreds of kHz), DOCT can be utilized not only on laminar, but also on turbulent flows [19]. When DOCT is combined with pressure loss (e.g., pipe flow) or shear stress (e.g., rotational rheometers) measurements, velocity profiling (i.e., calculation of local viscosities of the studied fluid) becomes possible.…”

Effects of salinity on the onset of elastic turbulence in swirling flow and curvilinear microchannels

“…The polymer type, concentration, solvent type and so on are both related to the occurrence of elastic turbulence. Different polymers such as PAM, PEO [18,46], DNA [47]and hydrolyzed PAM (HPAM) [19-21, 36, 48], due to the discrepancy of polymer relaxation time, chain length and molecular weight, have different onset values of elastic turbulence. Not only for polymers, it was found that micelles could induce similar elastic turbulence phenomena under some conditions [49][50][51][52].…”