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

Abstract

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 (Ca), i.e. at changing the balance between the viscous forces and the surface tension at the interface, up to Ca ≈ 3 × 10 −2 . A NavierStokes (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 Ca which is broad enough to characterize all the three characteristic mechanisms of breakup in the confined T-junction, i.e. squeezing, dripping and jetting regimes. The various model parameters of the FENE-P constitutive equations, including the polymer relaxation time τ 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 Droplet Viscoelasticity (DV), where viscoelastic properties are confined in the dispersed (d) phase, as well as cases with Matrix Viscoelasticity (MV), where viscoelastic properties are confined in the continuous (c) phase. Moderate flow-rate ratios Q ≈ 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.

Droplet breakup driven by shear thinning solutions in a microfluidic T-junction

“…[53], where it is shown that the LBM are actually able to capture sizable effects of non-Newtonian rheology on the droplet formation process. The present numerical work follows other studies by some of the authors [30,[54][55][56][57], where a NS description based on LBM has been coupled to constitutive equations for different polymer dynamics. Specifically, in two recent papers [54,55], three-dimensional (3D) simulations are carried out to quantify the effects of elasticity in the breakup processes in confined T-junctions [54] and cross-junctions [55], and to investigate the effects of thinning [30] in open microfluidic geometries [58,59].…”

“…Here the focus is instead on thinning effects in the T-junction geometry. We refer the interested reader to our previous papers where all the relevant LBM technical details are discussed [30,[54][55][56]. In Sec.…”

Pore‐Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media

“…The viscous pressure drop across each globule, and thus its ability to be displaced and recovered, is thus reduced. Due to their extensional viscosity, polymers are thought to suppress this breakup process-as shown in idealized experiments and simulations [201][202][203][204] -and thereby improve non-aqueous fluid recovery. Experiments on bulk rock cores show indirect agreement.…”

Lagrangian statistics of concentrated emulsions

“…The code has been extensively used and validated in the past by several groups to study: droplet deformation and breakup (Gupta, Sbragaglia & Scagliarini 2015), also in association with thermocapillary (Gupta et al. 2016) and viscoelastic (Gupta & Sbragaglia 2016) effects; droplet formation in microfluidic devices (Chiarello et al. 2017); sliding droplets (Varagnolo et al.…”