Stability and Realibility of microfluidic droplets storage in tube or storage coil
 

Hi,
I am trying to understand stability and reliability of droplet storage and transportation in microfluidic droplet storage coil or droplet storage tube which are used for droplet-on-demand systems.

Say I am creating water droplets in oil carrier ( or oil droplets in water carrier).

Length of droplets is Ld
Length of plugs between droplets or inter-droplet distance is Lp.
Length of the channel is Lc. Tube diameter is in microns and satisfies laminar flow condition with low Reynold number. The tube dimensions and geometry is constant over the entire length of the tube.

The diameter of droplet is about 10% larger than the diameter of the micro-tube so that droplets will occupy full cross section of the channel.
Assuming, I have achieved a steady state where equally spaced droplets with equal dimensions have fully occupied the length of the channel. i.e. a 1D droplet array has fully filled the channel.

Now I want to use this 1D droplet array library for further experiments and am applying pressure at one end of the storage tube and extracting the droplets form other end. What I want to know is-

1. Will there any change in Ld and Lc while extracting the droplets or I will be able to extract the droplets in exactly the same spatial ratio in which they are stored?

2. Will Ld and Lc change will applied pressure?

3. Will Ld and Lc change with flow velocity while extracting the droplets?

4. Will Ld and Lc change with channel length? I mean more the channel length –more the resistance-so more the pressure required to extract the droplets.

I am assuming there are no air gaps in the tube, so no compressible fluids are present. So we are dealing with non-compressible system with laminar flow. So ideally there should not be any changes in Ld and Lc that is the spatial orientation of the droplets should be very robust.

However what happens if the channel length increases? Can I make the droplet storage coil as long as I want and as narrow as I want without any limitations? At what length ( or resistance )of storage coil will the deviations start appearing? What happens if applied pressure and flow velocity increases? Under what conditions the ratio of Lc and Ld will be affected?

There are lot of studies and articles dedicated to droplet creation but I am not able to find much information on Droplet transportation and droplet storage in two phase (water-oil or oil-water) microfluidic systems.

Please let me know if there is any further reading material available relating the physics on the above topic.

Thanks