Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

Abstract

A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters—n and K in the power-law model—impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number (Ca) is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions.

Viscoelastic particle encapsulation using a hyaluronic acid solution in a T-junction microfluidic device

“…Under the qualitative point of view (Figure 2a), for the same set of imposed volumetric flow rate values, the droplet size did not differ significantly between Newtonian and non-Newtonian droplets, in agreement with previous finding on viscoelastic droplet microfluidics. 15,16,[28][29][30][31][32][33][34] However, we observed a clear difference in the dynamics of droplet formation between Newtonian and non-Newtonian droplets, with the presence of satellite droplet formation only observed for the non-Newtonian case, in agreement with previous findings featuring formation of viscoelastic droplets made of aqueous xanthan gum solutions in a commercial T-junction device. 15 We also quantified the droplet length L normalised by the channel width W = 100 µm, as a function of the ratio between the flow rate of the dispersed and the continuous phase (Figure 2(b-c)).…”

“…We observed that the data for viscoelastic droplet formation scaled with the same scaling as the Newtonian ones, thus suggesting that the droplet size is not affected by the fluid rheology significantly, in agreement with previous works. 15,16,[28][29][30][31][32][33][34] We also observed that the frequency of droplet generation scaled as f d = A (Q HA Q oil ) B with 6/9 A = 1.64 ± 0.18 and B = 2/3. The parameter A was obtained by fitting the entire data set with flow rate values in the units of µL/min, while B was fixed to B = 2/3 according to the previously introduced by Shahrivar and Del Giudice 15 for xanthan gum solutions.…”

“…35 3/9 Similarly, we observed that the normalised droplet length for non-Newtonian droplets scaled identically to the Newtonian case (Figure 2c), again reinforcing the qualitative observations in Figure2a, and previous findings on viscoelastic droplet microfluidics. 15,16,[28][29][30][31][32][33][34] In addition to the normalised droplet size, we also quantified the frequency of droplet formation (Figure 2d). This is a very important step in the pursue of controlled encapsulation, 9,10,15,16 because the Poisson stochastic limit can be overcome only when the frequency of droplet formation f d is equal to the constant frequency of equally-spaced particles f p approaching the encapsulation area.…”

Beating Poisson stochastic particle encapsulation in flow-focusing microfluidic devices using viscoelastic liquids

“…In other words, the fact that the data followed the scaling for Newtonian droplets may indicate that the droplet size is not significantly affected by the fluid elasticity. We observed a similar phenomenon in our recent work featuring viscoelastic droplets in Tjunction microfluidic devices [25], thus suggesting that fluid viscoelasticity impacts more the dynamics of droplet formation rather than the final size, agreement with other studies [8,[27][28][29][30][31][32]. Similarly to the droplet size, we also observed that the frequency of droplet formation f d scaled according to a mastercurve dependent upon the flow rate ratio q and the Capillary number Ca (Fig.…”

Design and Fabrication of Double-Layer Crossed Si Microchannel Structure

“…Most of the Si microchannel structures reported at present are in the same layer, in the shape of "T", "Y", comb, cross, Serpentine, and spiral [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. As the feature size of microdevices decreases and the integration degree increases, more complex design and more extended wiring are required in single-layer microchannels, which will affect the efficiency of the device operation.…”