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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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          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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          Condensed matter, Thermal physics & Statistical mechanics


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