PDMS-based turbulent microfluidic mixer

Abstract

Over the past decade, homogeneous mixing in microfluidic devices has been a critical challenge, because of the inherently low flow rates in microfluidic channels. Although several mixer designs have been suggested to achieve efficient mixing, most of them involve intricate structures requiring a series of laborious fabrication processes. Operation at high flow rates can greatly enhance mixing by induction of turbulence, but devices that can resist such a high pressure drop to induce turbulence in microfluidic channels are difficult to fabricate, especially for commonly used poly(dimethylsiloxane) (PDMS)-based microfluidic devices. We have developed a Y-shaped, turbulent microfluidic mixer made of PDMS and a glass substrate by strong bonding of the substrates to a nanoadhesive layer deposited via initiated chemical vapor deposition. The high bonding strength of the nanoadhesive layer enables safe operation of the PDMS/glass turbulent microfluidic mixer at a total water flow rate of 40 mL min(-1), corresponding to a Reynolds number, Re, of ~4423, one of the highest values achieved in a microfluidic channel. The turbulence generated as a result of the high Re allows rapid mixing of the input fluids on contact. Image analysis showed that mixing started as soon as the fluids were introduced into the mixer. The experimental results matched the numerical predictions well, demonstrating that convective mixing was dominant as a result of turbulence induced in the microfluidic channel. Using the turbulent microfluidic mixer, we have demonstrated high throughput formation of emulsions with narrower size distribution. It was shown that as the flow rate increases inside the microfluidic channel, the size distribution of resulting emulsions decreases owing to the increase in the turbulent energy dissipation. The turbulent microfluidic mixer developed in this work not only enables rapid mixing of streams, but also increases throughputs of microfluidic reactors.

Mixing in microfluidic devices and enhancement methods

“…Figure 1(a) shows a representation of the process of mixing by combining two channels into one channel in a microfluidic device. Mixing in such a device requires a long channel in order for full mixing to take place [27]. …”

“…The degree of mixing is minimal because the mixing is relying on diffusion alone (adapted from [27] with permission). (b) Scanning electron micrograph (SEM) of a mixer consisting of 2 × 15 interdigital channels with corrugated walls (adapted from [28] with kind permission from Springer Science and Business Media).…”

Rigorous buoyancy driven bubble mixing for centrifugal microfluidics

“…7,8,21 The mixing process is then considered complete, when a certain level of homogeneity in the grey scale distribution is achieved, and the required time is taken as a measure of the efficiency of the mixing system. Mixing is then relevant on a multitude of spatial scales, such that for example an enzyme gets into contact with the site where it can interact and at the same time cells that are considerably larger are kept in uniform suspension.…”

Chemical reaction engineering, process design and scale-up issues at the frontier of synthesis: Flow chemistry

“…4400). This was successfully applied to the emulsification of silicone oil in water under turbulent conditions [111].…”