Hi all,

I'm working with microfluidics-based double emulsions and I'm facing a recurring problem lately. I'm using a double-junction PDMS chip coated with 2,5% PVA, and, normally, I manage to produce highly monodisperse ultra-thin shelf double emulsions that remain stable for days. However, lately, I'm having trouble collecting them, because they all burst inside the chip, right before entering the collection tubing.

My solutions compositions are:

Inner solution: 15% (v/v) glycerol

Intermediate solution: 6,5 mM DOPC in 1-octanol

Outer solution: 15% (v/v) glycerol + 0,5% P188 (surfactant)

So far, I have tried everything that I could think of to troubleshoot this. The source of the problem seems to be chemical and not physical (something wrong with the solutions rather than with the chip, like bumps or obstructions in the channels). And it also seems to happen almost at random because sometimes everything works beautifully in one day, and I manage to collect plenty of perfectly stable double emulsions, but the following day, using the same reagents (the intermediate phase is always made fresh before use), nothing works.

Some of the things that I've tried so far:

- Reusing chips that had worked before

- Using freshly-made and coated chips

- Freshly made solutions: I always do the inner and outer solutions together and exactly the same way to try to balance their osmolarity as best as I can (we don't have an osmometer here). The intermediate phase I make fresh every time from a 10% lipid in ethanol stock solution, which I also make fresh from time to time to avoid the oxidation of the DOPC.

- Reusing inner and outer solutions that worked before.

- With and without the outlet tubing (changing the resistance of the system)

- Cutting the outlet tubing in different angles (flat or at-an-angle)

- Increasing the concentration of P188 to try to increase the stability of the double emulsions

I uploaded a video as an example of what happens. In this video, the solutions are exactly as described above, the pressures used in each inlet are mentioned at the end of the file name (ia29 means inner solution at 29mbar, for example, and these are the pressures that normally work well) and there is no tubing connected to the outlet of the chip, so it is easier to see what is happening. But the bursting happens regardless of it.

Thank you for your time! Any insight is welcome!

Kind Regards,

Camila