Extensional viscosity: A critical discussion

Petrie, C. J. S.

doi:10.1016/j.jnnfm.2006.01.011

Cited by 139 publications

(100 citation statements)

References 43 publications

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“…This is P r e p r i n t important as coupling between the extensional ('irrotational') and shearing ('rotational') deformations may lead to a significantly different microstructural response compared to a pure irrotational extensional deformation. Thus we emphasize that estimates of extensional material properties derived from contraction flows are only apparent measures (Petrie, 2006). This limitation notwithstanding, such flows can provide important insight into how complex fluids behave in mixed flows with strong elongational components, which are highly relevant to industrial applications such as inkjetting and of academic interest in their own right.…”

Section: Microfluidic Contraction Flowsmentioning

confidence: 99%

“…Classical macroscopic rheometry techniques for measuring fluid properties in shear and elongation typically involve characteristic length-scales O(1 mm), require sample volumes O(1 ml) and probe deformation rates of perhaps up to O(100−1000 s −1 ) (Macosko, 1994;Petrie, 2006). While these methods are satisfactory for understanding the behaviour of many fluids in a wide variety of flows, there are circumstances when using devices with smaller length-scales to investigate rheological response may be advantageous.…”

Section: P R E P R I N T 1 Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Microfluidic rheometry

Pipe¹,

McKinley²

2009

Mechanics Research Communications

226

161

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The development and growth of microfluidics has stimulated interest in the behaviour of complex liquids in microscale geometries and provided a rich platform for rheometric investigations of non-Newtonian phenomena at small scales. Microfluidic techniques present the rheologist with new opportunities for material property measurement and this review discusses the use of microfluidic devices to measure bulk rheology in both shear and extensional flows. Capillary, stagnation and contraction flows are presented in this context and developments, limitations and future perspectives are examined.

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Section: Microfluidic Contraction Flowsmentioning

confidence: 99%

Section: P R E P R I N T 1 Introductionmentioning

confidence: 99%

Microfluidic rheometry

Pipe¹,

McKinley²

2009

Mechanics Research Communications

226

161

View full text Add to dashboard Cite

show abstract

“…The vectorf is a force related to viscous and surface tension stresses, which we write using Trouton's model (30):…”

Section: Significancementioning

confidence: 99%

Whipping of electrified liquid jets

Guerrero

Rivero

Gundabala

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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We apply an electric field to a moderately conducting liquid surrounded by another coflowing liquid, all inside a glass-based microfluidic device, to study nonaxisymmetric instabilities. We find that the bending of the electrified jet results in a steady-state, helicoidal structure with a constant opening angle. Remarkably, the characteristic phase speed of the helicoidal wave only depends on the charge carried by the jet in the helicoidal region and its stability critically depends on the properties of the coflowing liquid. In fact, the steady-state helical structure becomes chaotic when the longest characteristic time is that of the inner liquid rather than that of the outer coflowing liquid. We also perform a numerical analysis to show that the natural preference of the jet is to adopt the conical helix structure observed experimentally.instability | charged jets | electro-coflow | electrospinning A liquid with finite electrical conductivity in the presence of a strong electric field can deform and adopt a conical shape resulting from the balance between electric and surface tension stresses (1). However, near the apex of the cone, this structure is not stable and the associated singularity is replaced by a thin jet (2-6). The resultant cone-jet structure, which is stable within certain values of the applied voltage and imposed liquid flow rate, is the workhorse of electrospray and all its associated applications (7-10).The jet that emanates from this structure always breaks into spherical droplets due to axisymmetric instabilities (11-13). However, in many cases, the jet bends off-axis due to a lateral instability that results from the electrostatic repulsion between bent and straight parts of the jet (14)(15)(16)(17)(18)(19). If the growth rate associated to this whipping instability is larger than that associated to jet breakup, the off-axis movement of the jet becomes the most significant aspect of its evolution. This is exploited in electrospinning, where the simple liquid is replaced by a polymer solution whose solvent evaporates before drop breakup takes place, thus resulting in the formation of polymer fibers (14,17,18,20). The presence of the lateral instability in this application results in thinner fibers, as bending stretches, concomittantly thinning the jet (20). Unfortunately, in most experimental realizations, whipping manifests in a chaotic fashion (15,16,18,19,21,22) preventing us from knowing and unraveling its detailed structure and properties.In this work, we apply an electric field to a moderately conducting liquid surrounded by a coflowing liquid to generate a steady-state whipping structure, which we find is helicoidal, with an amplitude that increases linearly along the downstream direction. Interestingly, the characteristic phase speed of the helical wave is determined by the electrostatic repulsion between the fluid elements of the jet in the whipping region. By performing a numerical analysis, we show that the conical helix structure is the natural configuration of electrified jets,...

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“…This resistance is characterized by the extensional viscosity, and the value of g E for viscoelastic solutions can be several orders of magnitude higher than the corresponding shear viscosities. [10][11][12][13] In many biological and industrial applications such as flow of biological fluids through contractions and valves, the flow of liquid foodstuffs through orifices, 14 or atomization of paints in an air-spray nozzle, the kinematics of the flow is dominated by elongational deformation, leading to dramatic effects of the extensional rheological properties on the flow.…”

Section: Introductionmentioning

confidence: 99%

“…11,13,15,16 In the last 20 years, specialized devices such as filament stretching instruments have been developed that can induce a a) Electronic mail: bavand@mit.edu local flow field in the fluid sample that is purely elongational; however, these instruments often fail to operate successfully for even moderately viscous liquids (g 0:1 Pa s). 17,18 For lower viscosity systems, an instrument based on the analysis of capillary thinning and breakup of liquid filaments was first introduced by Entov and coworkers 19 and later developed extensively by McKinley and coworkers and others.…”

Section: Introductionmentioning

confidence: 99%

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

Keshavarz

McKinley

2016

Biomicrofluidics

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Understanding the elongational rheology of dilute polymer solutions plays an important role in many biological and industrial applications ranging from microfluidic lab-on-a-chip diagnostics to phenomena such as fuel atomization and combustion. Making quantitative measurements of the extensional viscosity for dilute viscoelastic fluids is a long-standing challenge and it motivates developments in microfluidic fabrication techniques and high speed/strobe imaging of millifluidic capillary phenomena in order to develop new classes of instruments. In this paper, we study the elongational rheology of a family of dilute polymeric solutions in two devices: first, steady pressure-driven flow through a hyperbolic microfluidic contraction/expansion and, second, the capillary driven breakup of a thin filament formed from a small diameter jet (D j $ Oð100 lmÞ). The small length scale of the device allows very large deformation rates to be achieved. Our results show that in certain limits of low viscosity and elasticity, jet breakup studies offer significant advantages over the hyperbolic channel measurements despite the more complex implementation. Using our results, together with scaling estimates of the competing viscous, elastic, inertial and capillary timescales that control the dynamics, we construct a dimensionless map or nomogram summarizing the operating space for each instrument. Published by AIP Publishing. [http://dx

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Extensional viscosity: A critical discussion

Cited by 139 publications

References 43 publications

Microfluidic rheometry

Microfluidic rheometry

Whipping of electrified liquid jets

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

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