Particle alignment in a viscoelastic liquid flowing in a square-shaped microchannel

Abstract

We demonstrate the possibility to achieve 3D particle focusing in a straight microchannel with a square cross-section by exploiting purely viscoelastic effects. Experiments are carried out by considering an elastic, constant-viscosity aqueous solution of PVP (polyvinylpyrrolidone) as the suspending liquid. Several flow rates and two channel dimensions (with a fixed particle size to channel dimension ratio) are investigated. A novel technique combining particle tracking measurements and numerical simulations is used to reconstruct the position of the flowing particles over the channel cross-section. The results show that, for all the investigated experimental conditions, particles migrate towards the channel centerline. Flow-focusing is enhanced by higher flow rates. The measured particle fractions can be rescaled according to a single dimensionless parameter, as already reported in the literature for the case of cylindrical channels. The so-obtained master curve can be used as a guide to predict the required focusing length. The effect of the entrance on the focusing channel length is also addressed. Finally, analogies and discrepancies with similar previous works are discussed.

Size-Based Separation of Particles and Cells Utilizing Viscoelastic Effects in Straight Microchannels

“…The off-center focusing has only been reported by numerical studies (κ ≥ 0.25) and macroscale experiments (κ = 0.6). 54,56 Most existing studies manipulate particles or cells with κ around 0.1 in square microchannels, 27,35,36,42,48,57,[59][60][61] and thus this off-center focusing was not discovered in these experiments. This off-center focusing is quite different from that in inertial flow Page 6 of 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 of Newtonian fluids.…”

Is microrheometry affected by channel deformation?

“…10 In particular, particles suspended in a constant-viscosity but elastic fluid and subjected to a Poiseuille flow in a square-shaped microchannel migrate towards the centreline, 9,11 while particles suspended in a shear-thinning elastic fluid, in the same geometry, migrate towards the four corners. 9,11 When particles migrate towards the channel centreline, we showed 5 that the fraction of particles aligned at the centreline is related to the relaxation time k: hence, by determining the suspended particle distribution far from the channel inlet, we are in fact able to measure the (longest) relaxation time of the suspending medium.…”

“…%) was added to the solutions in order to prevent particle sedimentation. 9 The viscosity of the glycerol-water solution is g ¼ 2 Â 10 À3 Pa s. The fluid rheological properties are measured by a stress-controlled rheometer (Anton Paar MCR 302 rheometer), with cone and plate geometry with diameters of 50 mm and with a solvent-trap to avoid fluid evaporation. The fluids rheology is reported in Fig.…”

“…1932-1058/2016/10(4)/043501/9/$30.00 V C 2016 AIP Publishing LLC 10, 043501-1 depending on channel geometry 8,9 and on fluid rheology. 10 In particular, particles suspended in a constant-viscosity but elastic fluid and subjected to a Poiseuille flow in a square-shaped microchannel migrate towards the centreline, 9,11 while particles suspended in a shear-thinning elastic fluid, in the same geometry, migrate towards the four corners.…”

“…While our previous analysis 5,9 has been carried out in Poly(methylmethacrylate) (PMMA) microchannels, most of the microrheometrical measurements available in literature have been carried out in Poly(dimethylsiloxane) (PDMS) channels, bonded on a glass coverslip. In fact, PDMS is the most used material for the fabrication of microfluidic devices.…”