Microscopic origin of wall slip during flow of an entangled DNA solution in microfluidics: Flow induced chain stretching versus chain desorption

Abstract

Despite the relevance and importance of slip, a fundamental understanding of the underlying molecular mechanisms of wall slip in polymer flow is still missing. In this work, we investigate the slip behavior of an entangled DNA solution at a molecular scale using a confocal microscope coupled to a microfluidic device. From microscopic measurement, we obtain both the velocity profile and conformation of polymeric chains by visualizing DNA molecules during flow on various surfaces (ranging from weak to strong interactions with DNA molecules). In channel flow at a low Weissenberg number (Wi = 0.14), we observe a parabolic flow for an APTES-treated glass (with strong interaction with DNA) in the absence of slip, while a significant amount of slip has been observed for a regular glass (with a weak interaction with DNA). At higher flow rates (Wi > 1.0), strong slip appears during flow on APTES-treated surfaces. In this case, only immobile DNA molecules are stretched on the surface and other bulk chains remain coiled. This observation suggests that the flow induced chain stretching at the interface is the main mechanism of slip during flow on strong surfaces. Conversely, for slip flow on surfaces with weak interactions (such as unmodified or acrylate-modified glasses), polymeric chains are desorbed from the surface and a thin layer of water is present near the surface, which induces an effective slip during flow. By imaging DNA conformations during both channel and shear flows on different surfaces, we elucidate that either chain desorption or flow-induced stretching of adsorbed chains occurs depending on the surface condition. In general, we expect that these new insights into the slip phenomenon will be useful for studying the biological flow involving single DNA molecule experiments in micro/nanofluidic devices.

Influence of Polymer Concentration and Nozzle Material on Centrifugal Fiber Spinning

“…However, this no-slip boundary condition will not be valid for many complex fluids, such as polymer solutions. Especially at higher polymer concentrations things become even more complicated when a thin polymer-depleted layer of much lower viscosity than the bulk solution forms at the solid boundary, in which the surface wettability plays a crucial role [73][74][75][76][77]. One of the open questions in centrifugal spinning that has not been dealt with in detail, to our knowledge, is the effect of nozzle material on the final fiber morphology.…”

Single polymer dynamics for molecular rheology

“…In a first study, calf thymus DNA (polydisperse, average molecular size of ≈75 kbp) was prepared at three different concentrations in an aqueous salt buffer corresponding to three levels of entanglement: Z = 24, 60, and 156 entanglements per chain [210]. 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].…”

“…It was found that interfacial chain disentanglement results in wall slip beyond the stress overshoot, and disentanglement generally produces tumbling motion of individual DNA in the entangled solutions under shear. More recently, the phenomenon of wall slip was studied by single molecule imaging near adsorbing and non-adsorbing boundaries[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].…”

Effect of edge disturbance on shear banding in polymeric solutions

“…To mitigate the influence of edge instabilities, shearbanding experiments with sample edges wrapped in plastic films [5], in large-aspect-ratio shear cells with small gaps [8,[27][28][29] and using a special cone-partitioned-plate rheometer [30] have been conducted. However, it is still debatable whether these procedures truly eliminate the edge instabilities [14].…”