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Micro-mixer We have a winner! The inventors have picked An aerogel more transparent by Michel Daubizit as the winner for this competition. Here's what they had to say:

“We are pleased with the contribution made by the crowd. The application suggested and elaborated by Michel takes advantage of the unique features of our current micromixer, and so this distinguishes itself from other designs. And the idea is feasible as it is relatively easy to implement without requiring many other supporting techniques to be developed.”
- Dr Kim Wui Chee, ETPL

 

Liquids behave a bit strangely if you confine them in very narrow channels, as you do in microfluidics. One important effect of this small scale is that you get something called “laminar flow” – when two channels merge, the inputs from each simply flow alongside each other instead of mixing as you might expect. Not brilliant if you want those two inputs to react!

We have developed a simple, non-powered device that can be added in-line to convert this laminar flow to oscillatory flow, achieving effective mixing in milliseconds.
 
Diagram of a Y-junction with the micromixer embedded in one of the arms showing transition from laminar to turbulent flow and high-speed recording of mixing at a Y-junction.

As you can see below, the device contains an inlet, an outlet, and a fluid chamber with a stepped sidewall that holds an elastic diaphragm. When a liquid is pumped through the device above a certain pressure, spontaneous vibration of the diaphragm will be produced, thus changing the stable laminar flow to high-frequency oscillatory flow.
 
Schematic of the mixer depicting the deformation and oscillation of the elastic diaphragm at increasing pressures. 

As no external actuators (such as piezoelectrics or magnetic systems) are involved, the structure of the device is very simple and can be easily fabricated at low cost (several US$ at large scales, 10s of US$ at low numbers). Other passive systems, which typically rely on complex static geometries, achieve much lower throughput and slower mixing (typically a few seconds). However, it’s important to note our device kicks the bucket after about a certain time (typically around 10h) of continuous use.

Sponsored by the Royal Society of Chemistry.

Your mission
The device was developed during a fundamental study on techniques to enhance microfluidic mixing (which it’s very good at!), with only a few real-world applications (in synthetic chemistry) in mind. At the moment it’s mainly just a cool piece of technology looking for some problems to solve.

We are currently exploring its application for nanoparticles synthesis – however, it may potentially be used for a huge range of chemical or biological processes where rapid mixing of chemical reactants, bio-samples or other reagents is required.

And that’s where you come in. We’re interested in both commercial and academic applications of the technology. A great submission would:
  • Derive a competitive advantage in a field from the device’s unique features, i.e. the fact it achieves rapid, high-throughput mixing without the use of external actuators (keeping in mind the device starts degrading after ca. 10h).
  • Be specific in terms of technical implementation.
  • Clearly outline the path to adoption: Which research groups/companies should we talk to? Would the device need to be altered? Who’d be the end user?
Key features
  • Simple structure: the device makes use of the spontaneous vibration of the diaphragm; no actuators and controllers are involved.
  • High oscillation frequency: typically ranges from several tens to several hundred Hz, achieving rapid mixing.
  • Operable pressure range: 0.3 bar ~ 6.5 bar, applied via a pump or manually via a syringe. Higher pressure is required for higher viscosity liquids (viscosity ~60 cP (think olive oil) possible at 6.5bar)
  • Chamber diameter 0.1 - 1 cm (note that this refers to the chamber diameter, not that of the flow channel, which will be significantly smaller) with flow rate 1.2 - 80 ml/min. 
  • Can make the chamber out of most materials (plastic, glass, metal…). The diaphragm must be elastic – rubber or, for high temperature applications (>100°C possible), spring metal
  • Operable for a certain amount of time (10h for mid-range flow parameters), after which material degradation sets in because of the rapid oscillation.
  • Device automatically acts as a pressure-limiting valve and one-way valve, i.e. blocks high-pressure and reverse flow respectively. However, can be designed to produce oscillatory flow in each direction.

The story behind the science
The SIMTech Microfluidics Foundry (SMF) is established by the Singapore Institute of Manufacturing Technology (SIMTech), a research institute of the Agency for Science, Technology and Research (A*STAR), to advance the microfluidic technology as well as nurture and grow the microfluidics industry in Singapore by providing the infrastructure, support and manufacturing solutions to the academic and industrial community.

The Microfluidics Manufacturing Programme (MMP) is an application-oriented programme that harnesses the capabilities of SIMTech’s core technology groups to develop and implement a complete set of manufacturing processes for polymer-based microfluidic devices.

With Marblar, we hope we can speed up the movement of some of the exciting technologies we've developed from laboratory to market. Excited to see your ideas!

More information
International patent application WO 2012/036627 A1

H. M. Xia et al., Converting steady laminar flow to oscillatory flow through a hydro-elasticity approach at micro scales, Lab Chip, 2012, 12, 60-64.

Review on microfluidic mixing (background reading)
Challenge Discussion
Valeriy Stepanov on Aug 01, 2013
Valeriy Stepanov
At its core, the device is a hydrodynamic whistle. Then the membrane can be made of any elastic material to fix it at the nodes of flexural vibration and place along the stream. The membrane will emit over a wide range of flow velocities. The product may have various sizes.

Luc Marti on Aug 01, 2013
Talking about various sizes, do the inventors think it could be scaled down to nanofluidic mixer?
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Benjamin Wade on Jul 18, 2013
Forgive me if this very off base, but, assuming the oscillatory rate is fixed based on pressure and viscosity, is the oscillation rate high enough (and stable enough) to generate controllable ultrasound, and if so, can anyone think of a use for small scale ultrasonography? This may be a very stupid idea/question because I know ultrasonic transducers can be made very small.
Huanming Xia (Inventor) on Jul 18, 2013
The typical oscillation frequence ragnes from several tens to several hundred Hz. It could be further increased through scaling down the device and using very thin (less mass) diaphragm. But it will be very difficult, if not impossible, to reach the ultrasound range.
Benjamin Wade on Jul 18, 2013
Sorry, my ignorance is showing ;-)
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Thijs Van den Brande on Jul 10, 2013
What is the maximum difference in flow rates from the two channels? Is it possible to use it for two flow rates where one is much larger ( >100x ) compared to the other?
Huanming Xia (Inventor) on Jul 10, 2013
Yes, it is possible. The liquid through the oscillator-mixer should be driven by a pressure pump, and the flow rate is determined by the pressure difference upstream and downstream of the device. For the liquid through the other channel, its flow rate can be controlled separately. So long as the second branch flow will not affect the pressure downstream the oscillator, the flow rate through the oscillator mixer will remain constant. Otherwise, calibration on the flow rate may be required.
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Alan Tennant on Jul 03, 2013
Can liquids be mixed like this that wouldn't mix otherwise or mix in a different way when combined in larger spaces?

Are there any applications for tiny amounts of chemical that never mix packed into a tiny tube in an adjacent sequence?
Kim-Wui Chee (Inventor) on Jul 03, 2013
Hi Alan, do you have any application in mind? The invention is a micro-litre mixer, so it works in tiny tube.
Alan Tennant on Jul 03, 2013
No, sorry.
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mark wareing on Jul 02, 2013
Could the elastomer be fed through on a 'continuous' belt or a revolving cartridge containing replacement diaphragm discs - to exceed the 10 hour life? The device then should have more potential for manufacturing processes - assuming larger bore tubing can also work? Mark Wareing
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devon cayer on Jul 01, 2013
Could you somehow put this thing on a patch to where someone could have their blood flow through it to monitor their blood pressure? For high risk individuals you could have a system where it mixes with a dye to turn green when lower pressure, and red when higher pressure. Give it to people who have heart problems.
Kim-Wui Chee (Inventor) on Jul 01, 2013
Hi Devon, how would this be better than the blood pressure pump?
Gabriel Mecklenburg on Jul 01, 2013
Hey Devon, I'm pretty sure this would pulverize the blood cells moving through the mixer :)
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Merijn van Wouden on Jun 25, 2013
Now I can finally serve cocktails to my pet ants
Kim-Wui Chee (Inventor) on Jun 25, 2013
Hi Merijn, that is a great angle to look at this. We just need to find a business model.
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Colin Patterson on Jun 25, 2013
This reminds me of a similar technology developed by Professor Xiong-Wei Ni if NiTech Solutions (www.nitechsolutions.co.uk/). Slightly larger scale however!
Kim-Wui Chee (Inventor) on Jun 25, 2013
In fact Dr. Xia have another invention that is on chaotic mixing with microfluidics chip that is mented for personal care product mixing with high viscosity ratio of up to 60,000. Patent (WO2011078790) is now been filed for National coversion.
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Barry Nicholson on Jun 25, 2013
This would be a potentially better/cheaper method for mixing two part epoxies. Currently, 3M use a gun with long nozzles with spirals to allow mixing and deposition. The nozzles are quite long and are thrown away after mixing, so a shorter, cheaper version would be great. They are relatively low flowrate (plunger) so would seem to fit the bill, and lifetine needs to be a few seconds to be effective. Pressure might be an issue due to the high viscosity of epoxy fluids. Having said all that, I would have though a simple hard bluff object would achieve good mixing by vortex shedding? Might improve the lifetime.
Gabriel Mecklenburg on Jun 25, 2013
Hi Barry,
I think you're right - the viscosity will be an issue. Even the most liquid epoxies have a viscosity an order of magnitude above the maximum compatible with this technology [1].
In addition, you wouldn't really need microfluidic mixing, do you? In this case a more macro structure like you suggest would work. These are used in microfluidics as well by the way - but they show much lower throughput and slower mixing than this device.

[1] msdssearch.dow.com/Publishe...
Barry Nicholson on Jun 25, 2013
Well the main advantage would be the lower volume of lost product in the mixing tube, as well as a better final strength, which depends a lot on the quality of mixing. What is indicated in the brief is a chamber size of 0.1 to 1cm - hardly microfluidic range - unless there's a unit problem - and a flowrate up to 80 cc/min - which is pretty substantial. My only other idea was "instant" mayonnaise from vegetable oil and water!
Gabriel Mecklenburg on Jun 25, 2013
Hi Barry,
The chamber diameter is different from the diameter of the flow channel, which is still expected to have microfluidic dimensions. I've clarified this in the text now - thanks for flagging that up.
However, you are of course right - 80cc/min is quite substantial, making the device suitable for fairly high-volume applications. However, the epoxy will be too viscous I fear.
Kim-Wui Chee (Inventor) on Jun 25, 2013
Hi Barry, this may be an angle that we can explore with our other mixing device. Do you have in road to 3M on this disposable mixing tip?
Barry Nicholson on Jun 25, 2013
Hi, I have a cousin who is involed in this industry, though not 3M directly (competitor, actually). I can have a chat with him, as there may be other applications he can see (paints, in particular). There are some ultra-thin epoxies out there, used for penetrating gaps in concrete, etc., so there is a market, but would be more niche. Let me have some details or reference on this other device.
Huanming Xia (Inventor) on Jun 25, 2013
The high viscosity of epoxies could be an obstacle for this application. So far the maximum applicable viscosity we have tested is around 60 cP (60 times that of water). Higher viscosity is possible, but requires higher pressure. What is the viscosity range of the ultra-thin epoxies you have mentioned? thanks!
Barry Nicholson on Jun 25, 2013
Hi, they are about 40 to 140cp:
nextstar.ca/shop/item.aspx/...
www.euclidchemical.com/prod...
or just google "ultra low viscosity epoxy".
Gabriel Mecklenburg on Jun 25, 2013
Hey Barry, you should submit this as an entry - looks like you might be on to something :)
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Wayne Martin on Jun 25, 2013
This reminds me of a fluid transistor developed during the space program. The flow was in the opposite direction of your device and consisted of high pressure air. Small ducts on the sides of the single pipe could, with a puff of air, 'switch' the laminar flow between the other two pipes in the 'Y'. Or, with a balance puff from both, cause the flow to split between both. Just a fun similarity.
Kim-Wui Chee (Inventor) on Jun 25, 2013
Thanks. Is that fluid transistor be made of a larger scale? Would such device also create a laminar flow?
Huanming Xia (Inventor) on Jun 25, 2013
Thanks. The transistor sounds like a Coanda-type fluidic oscillator. It usually works at higher Reynolds numbers, or high flow rate.
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Carlos Cluff on Jun 24, 2013
possible application is in the neo-natal timed drugs administration\dosing process to shrink the sizes of the pumps and to keep some of the medicines that are in suspension form continually mixed while being administered since the heat involved from the mixing chamber is minimal it wouldn't cause a degradation of the needed medicines.
Gabriel Mecklenburg on Jun 24, 2013
Hi Carlos, this would make a great entry - I think that's a really interesting idea!
Carlos Cluff on Jun 24, 2013
I made the idea an entry. thanks for the suggestion.
Huanming Xia (Inventor) on Jun 24, 2013
Interesting idea. The device is manually operable. If there is the need of mixing different components before injection, we may just use a common syringe and attahed the mixer to it as a disposable mixing component. For mixing liquids, a static mxier will do the work. but for mixing suspensions, it may be a better solution.
Carlos Cluff on Jun 24, 2013
During a Neo-natal intensive care unit stay there are many times where the powders are put in to a suspension form and then administered. the goal would be to keep the powders in suspension. and in correct dosages. this being said having the ability to have the compunded powder sent up to the patient rather than a liquid which needs refrigerated and then mixed at the patients side would be far superior to having a premixed suspension.
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Tim Tim on Jun 24, 2013
I have a commercial use for this now at the larger scale of 0.5cm - 1cm diameter. You say the device lasts 10 hours due to wear, However our mixing times are done in spurts, meaning a 10 hour continuous operation might be split over a manufactured volume of product, for many days.

If the mixing diameter is larger does the wear timing factor change? If so what would be your best guesstimate of components lifetime?
Gabriel Mecklenburg on Jun 24, 2013
Hey,
The life-time is based on fatigue of the material resulting in changes in elastic properties as well as plastic deformation. The exact time will depend on materials choice (fatigue resistance varies quite a lot between spring steels) and flow parameters. The 10h time-scale is meant mainly as an order-of-magnitude estimate and to emphasize that the device can only ever be used for limited periods of time, rather than built into a permanent structure.
Huanming Xia (Inventor) on Jun 24, 2013
Scaling-up of the component may not affect its lifetime. The diaphragm lifetime is more influenced by the applied pressure which can vary from 10^4 ~10^6 Pa, or even higher. The lower the pressure (or the smaller oscillation amplitude), the longer the lifetime of the vibrating diaprhagm.
Kim-Wui Chee (Inventor) on Jun 24, 2013
Hi Tim Tim, what are you curently mixing at a commerial scale which you see a possible application of this mixer?
Tim Tim on Jun 24, 2013
Part A and Part B polyurethane.
Gabriel Mecklenburg on Jun 24, 2013
Hey Tim - looking forward to that entry :)
Tim Tim on Jun 24, 2013
I'm not entering anymore - maybe help on a few entries and observe only from now on.
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