Extensional Flow of Entangled DNA Solution in Microfluidic Devices

Complex fluids from colloids, DNA and synthetic polymers, liquid crystals, micelles, foams, gels, emulsions to membranes are ubiquitous around. These materials respond elastically or solid-like with a deformation rate exceeding slowest relaxation rate (Wi >1.0). Extensional flow of complex fluids is important in many practical operations from spraying of paint, roll coating of adhesive to fiber spinning, extrusion, and film blowing of polymeric fluid. Typically, the extensional flow behavior of non-Newtonian fluids is terminated by the appearance of unstable necking or rupture-like failure. Although there have been theoretical attempts to interpret failure during extension, still molecular mechanism for necking and rupture-like failure is un-known. The aim of this work is to use entangled DNA solutions as model to unravel the molecular origin of necking during extension.

Here, we employ micro-droplet microfluidics and fluorescently labeled DNA to study the flow instability with respect of necking of a DNA solution undergoing extensional flow. We investigated different kinds of failure in entangled DNA solutions by capturing the molecular response of DNA during extension. These new experimental findings provide new insight into the mechanistic origins of different failure in the extensional flow of entangled fluids.