Microfluidic extensional rheometry using a hyperbolic contraction geometry

Abstract

Microfluidic devices are ideally suited for the study of complex fluids undergoing large deformation rates in the absence of inertial complications. In particular, a microfluidic contraction geometry can be utilized to characterize the material response of complex fluids in an extensionally-dominated flow, but the mixed nature of the flow kinematics makes quantitative measurements of material functions such as the true extensional viscosity challenging. In this paper, we introduce the 'extensional viscometer-rheometer-on-a-chip' (EVROC), which is a hyperbolically-shaped contractionexpansion geometry fabricated using microfluidic technology for characterizing the importance of viscoelastic effects in an extensionally-dominated flow at large extension rates (λε a 1, where λ is the characteristic relaxation time, or for many industrial processesε a 1 s −1 ). We combine measurements of the flow kinematics, the mechanical pressure drop across the contraction and spatially-resolved flow-induced birefringence, to study a number of model rheological fluids as well as several representative liquid consumer products in

Micro-scale extensional rheometry using hyperbolic converging/diverging channels and jet breakup

“…The pressure drop across the hyperbolic contraction DP c is evaluated from the pressure difference measured between the 2nd and 3rd sensors DP 23 with a minor extrapolation upstream and downstream of the pressure transducers to correct for the fact that they are not located exactly at the throat entrance/exit of the converging/ diverging region. 56 From Equations (1) and (2), it is clear that by varying the flow rate in the channel the apparent extension rate in the constriction is controlled, and measuring the pressure drop across the contraction then gives a direct measure of the viscoelastic effects involved in the deformation of material elements as they flow through the contraction/expansion. …”

“…Early studies of polymeric flows in contractions [45][46][47][48][49][50][51] showed many promising aspects and its relevance to commercial polymer processing operations such as injection molding established the contraction flow as a ubiquitous "rheological indexer" for elongational properties. Several recent studies, [52][53][54][55][56] benefiting from advances in fabrication techniques for microfluidic channels, have focused on the flow of complex liquids in hyperbolic contraction geometries asserting that the hyperbolic profile will aid in maintaining the apparent stretch rate _ a constant throughout the contraction. 52,57 The recent study by Ober et al 56 investigated a microfluidic hyperbolic expansion/contraction flow for a variety of different low viscosity test fluids and outlined methods based on two-dimensional lubrication theory to measure elongational properties based on pressure drop measurements across the contraction.…”

“…Thus, in this study, we attempt to measure the elongational properties of a family of dilute polymer solutions by using two separate devices representing the different classes described above. Results from a microfluidic hyperbolic contraction device or "extensional viscometer-rheometer-on-a-chip" (EVROC), similar to the device used by Ober et al, 56 are compared with jet breakup studies performed with the ROJER setup. This latter configuration focuses on the transient growth in the extensional viscosity for an unknown viscoelastic test sample at a single (nominally) constant strain rate that is set by the viscoelastic and interfacial properties of the fluid.…”

Wellbore to fracture proppant-placement-fluid rheology

“…In this case the fluid has a non-zero velocity gradient in the direction of flow du x / dx -0, known as the extension rate and extra flow resistance is caused by the presence of extensional viscosity (Macosko, 1994). In addition, for VES fluids, an elastic contribution results in much higher pressure drops over an expansion or contraction (Ober et al, 2013). As such, it is important to determine whether SIS fluids exhibit viscoelastic properties when undergoing extensional flow indicating if the preferential flow-induced viscoelasticity is present in the near-wellbore and in this way can potentially aid proppant suspension.…”

“…2. Schematic of the EVROC microfluidic cell used for extensional resistance experiments (Ober et al, 2013). Fig.…”