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# Effects of viscoelasticity on droplet dynamics and break-up in microfluidic T-Junctions: a lattice Boltzmann study

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### Abstract

The effects of viscoelasticity on the dynamics and break-up of fluid threads in microfluidic T-junctions are investigated using numerical simulations of dilute polymer solutions at changing the Capillary number ($$\mbox {Ca}$$), i.e. at changing the balance between the viscous forces and the surface tension at the interface, up to $$\mbox{Ca} \approx 3 \times 10^{-2}$$. A Navier-Stokes (NS) description of the solvent based on the lattice Boltzmann models (LBM) is here coupled to constitutive equations for finite extensible non-linear elastic dumbbells with the closure proposed by Peterlin (FENE-P model). We present the results of three-dimensional simulations in a range of $$\mbox{Ca}$$ which is broad enough to characterize all the three characteristic mechanisms of breakup in the confined T-junction, i.e. $${\it squeezing}$$, $${\it dripping}$$ and $${\it jetting}$$ regimes. The various model parameters of the FENE-P constitutive equations, including the polymer relaxation time $$\tau_P$$ and the finite extensibility parameter $$L^2$$, are changed to provide quantitative details on how the dynamics and break-up properties are affected by viscoelasticity. We will analyze cases with $${\it Droplet ~Viscoelasticity}$$ (DV), where viscoelastic properties are confined in the dispersed (d) phase, as well as cases with $${\it Matrix ~Viscoelasticity}$$ (MV), where viscoelastic properties are confined in the continuous (c) phase. Moderate flow-rate ratios $$Q \approx {\cal O}(1)$$ of the two phases are considered in the present study. Overall, we find that the effects are more pronounced in the case with MV, as the flow driving the break-up process upstream of the emerging thread can be sensibly perturbed by the polymer stresses.

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###### Journal
1508.00141

Condensed matter, Thermal physics & Statistical mechanics