A soft microchannel decreases polydispersity of droplet generation

Abstract

We study the effect of softness of the microchannel on the process of droplet generation in two-phase flows in a T-junction microchannel. One side of the microchannel has a flexible thin PDMS layer, which vibrates naturally while droplets are generated; the deformation frequency coincides with the frequency of droplet formation. Furthermore, we compare the polydispersity of water-in-oil droplets formed with a microchannel with one soft wall with those formed in a conventional rigid microchannel. We show that deformation of the soft wall reduces the polydispersity in the droplet size.

Droplet generation in a microchannel with a controllable deformable wall

“…A reduction of more than 50 % in the polydispersity value can be observed as compared to that of a rigid droplet generator of identical dimensions. In our case, polydispersity value was measured to be 0.015 at Ca = 0.22, which compares well with that obtained for a single-layer soft microchannel droplet generator reported by Pang et al (2014). Figure 10 shows a comparison of the polydispersity in the droplet size produced using the rigid versus deformable droplet generators.…”

“…The influence of flow rate ratio r (ratio of the flow rates of the discrete phase to that of the continuous phase), viscosity ratio λ (ratio of the viscosity of the discrete phase to that of the continuous phase) and the capillary number (Ca) (i.e., interplay between surface tension and viscous forces and defined as Ca = μU/σ, where U is the velocity of the continuous phase flow, µ is the dynamic viscosity of the continuous phase fluid, and σ is the interfacial tension of the discrete and continuous phase interface) on the size of the droplets formed at a T-junction is well studied in the literature, and correlations are reported (Adzima and Velankar 2006;Christopher and Anna 2007;Gupta and Kumar 2009). However, in a flowfocusing device, one single model cannot be used to correlate the droplet breakup as a function of various control parameters (Christopher and Anna 2007;Nie et al 2008). It is reported that, at low Ca and viscosity ratio, the size of the droplet formed is governed by the flow rate ratio of the two phases (Zhang and Stone 1997).…”

“…Recently, it is reported that the formation of droplets in a soft microchannel reduces the polydispersity of droplets (Pang et al 2014). In another work, the droplet breakup junction included a controllable moving-wall structure, which enabled the formation of droplets of size smaller than the junction diameter (Lin et al 2008).…”

Rivulet flow over a flexible beam

“…The general topic of elastohydrodynamics concerns problems where fluid flow is coupled to the deformation of an elastic boundary (Gohar 2001;Dowson & Ehret 1999). Examples include the flow induced deformation of an elastic object or boundary during collision (Davis et al 1986), droplet generation in a soft microfluidic device (Pang et al 2014), and the lift force on a sedimenting object generated by sliding motions accompanied by elastic deformation (Sekimoto & Leibler 1993;Skotheim & Mahadevan 2005;Salez & Mahadevan 2015). There are many natural examples related to a local flow-induced deformation, e.g.…”

Is microrheometry affected by channel deformation?

“…The effect of wall stiffness on fluid-dynamic in microchannels has itself received great attention in the last decade. 20,[22][23][24][25] Gervais et al 22 and Hardy et al 20 theoretically and experimentally showed that PDMS channel walls are deformed under the effect of an imposed pressure-driven flow. These results were also confirmed in more recent experimental studies.…”