Effect of fluid relaxation time of dilute polymer solutions on jet breakup due to a forced disturbance

Christanti, Yenny; Walker, Lynn M.

doi:10.1122/1.1463418

Cited by 112 publications

(116 citation statements)

References 27 publications

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“…The data are plotted as a function of molecular weight in Figure 1. Also shown in the figure are the results obtained by other researchers, both in this laboratory 38,39 and elsewhere 37,40 , in water and glycerol/water mixtures. The molecular weights of the PEO span a range from The critical overlap concentration c* is defined as the concentration at which the polymer coils start to overlap with each other.…”

Section: Intrinsic Viscosity and Zimm Relaxation Timementioning

confidence: 62%

“…The exponential decay in time has been observed in viscous polymer solutions corresponding to 1 Oh >> 26 and also in low viscosity solutions (Oh << 1) 34,35,37 . It is worth noting that in this exponential necking regime, the flow in the thread is a homogeneous uniaxial elongation with a constant extension rate Very close to the final breakup event at t b the finite extensibility of the molecules becomes important.…”

Section: (3 )mentioning

confidence: 87%

“…In Christanti and Walker 37 , analysis of the video images showed that the relaxation times determined from the rate of jet radius reduction were a factor of two higher than the Zimm values, although these authors suggested that such differences were more a result of experimental error than a matter of physical significance. It should also be noted here that the Zimm relaxation times quoted by Christanti and Walker 37 were calculated based on a numerical front factor of 0.95 and were higher than they would have been if calculated using the front factor of 0.463 determined for PEO in a good solvent with solvent quality index of 0.55, as used here.…”

Section: B Effects Of Polymer Molecular Weightmentioning

confidence: 96%

“…Recent experiments in low-viscosity dilute polymer solutions exiting a nozzle and undergoing breakup under the effect of gravity 35 have shown that similar dynamical phenomena are observed in a continuous jet undergoing breakup 36 , and under forced disturbances of a known wavelength 37 . The resulting dynamics are always found to vary strongly with the molecular weight of the dissolved macromolecules, and differ significantly from those observed in a Newtonian fluid.…”

Section: A Model For Inertio-elastic Pinchingmentioning

confidence: 99%

“…Recent experimental studies in dilute polymer solutions with Oh << 1 have shown that following the formation of a slender thread of the type shown in Figure 3 for the 0.1wt% PEO solution, there is an analogous crossover to an exponential rate of necking 29,30,34,37 .…”

Section: A Model For Inertio-elastic Pinchingmentioning

confidence: 99%

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Drop formation and breakup of low viscosity elastic fluids: Effects of molecular weight and concentration

2006

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The dynamics of drop formation and pinch-off have been investigated for a series of low viscosity elastic fluids possessing similar shear viscosities, but differing substantially in elastic properties. On initial approach to the pinch region, the viscoelastic fluids all exhibit the same global necking behavior that is observed for a Newtonian fluid of equivalent shear viscosity. For these low viscosity dilute polymer solutions, inertial and capillary forces form the dominant balance in this potential flow regime, with the viscous force being negligible. The approach to the pinch point, which corresponds to the point of rupture for a Newtonian fluid, is extremely rapid in such solutions, with the sudden increase in curvature producing very large extension rates at this location. In this region the polymer molecules are significantly extended, causing a localized increase in the elastic stresses, which grow to balance the capillary pressure. This prevents the necked fluid from breaking off, as would occur in the equivalent Newtonian fluid. Alternatively, a cylindrical filament forms in which elastic stresses and capillary pressure balance, and the radius decreases exponentially with time. A (0+1)-dimensional finitely extensible nonlinear elastic dumbbell theory incorporating inertial, capillary, and elastic stresses is able to capture the basic features of the experimental observations. Before the critical “pinch time” tp, an inertial-capillary balance leads to the expected 2∕3-power scaling of the minimum radius with time: Rmin∼(tp−t)2∕3. However, the diverging deformation rate results in large molecular deformations and rapid crossover to an elastocapillary balance for times t>tp. In this region, the filament radius decreases exponentially with time Rmin∼exp[(tp−t)∕λ1], where λ1 is the characteristic time constant of the polymer molecules. Measurements of the relaxation times of polyethylene oxide solutions of varying concentrations and molecular weights obtained from high speed imaging of the rate of change of filament radius are significantly higher than the relaxation times estimated from Rouse-Zimm theory, even though the solutions are within the dilute concentration region as determined using intrinsic viscosity measurements. The effective relaxation times exhibit the expected scaling with molecular weight but with an additional dependence on the concentration of the polymer in solution. This is consistent with the expectation that the polymer molecules are in fact highly extended during the approach to the pinch region (i.e., prior to the elastocapillary filament thinning regime) and subsequently as the filament is formed they are further extended by filament stretching at a constant rate until full extension of the polymer coil is achieved. In this highly extended state, intermolecular interactions become significant, producing relaxation times far above theoretical predictions for dilute polymer solutions under equilibrium conditions.

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