Calculations and general musings about droplet diameter control.

Some sphere calculations:

So if the goal is 100 um, the syringe should be able to dispense 520 pL of fluid with a certain plunder displacement. The minimum usable displacement will be decided by the minimum step size of the stepper motor.

Needle point types: http://www.hamiltoncompany.com/Syringes/techInfo/pointStyle.php

Some potential syringes: http://www.hamiltoncompany.com/products/syringes/c/800/

(Sigh, these links are now dead...)

The lowest volume one can dispense 5 uL, which means I would want to dispense about 1/10000 of the volume at one time. If the plunger travel distance is 10 cm, I would need to be able to push it at 10 um increments. Can stepper motors do that?

Another option would be to push the ferrofluid out slowly, relying on the speed of the oil to tear drops away from the needle quickly. If I can get 1 mm/second (not sure about this) I would need to produce 100 drops/second.

Smaller gauge needles should let go of drops of lower volume, everything else being equal. My hypothesis is that a droplet will release when it is of larger diameter than the outside of the needle, given a flow of fluid past it. If that's true, I can control droplet size through needle diameter. Gauge 34 needles have an outer diameter of 184.2 um. (But would they be strong enough to pierce a plastic tube?)

Apparently you can model pipe diameter and fluid pressure like resistance and voltage. If I get a small gauge needle, I might not have to worry about moving the plunger slowly. The goal might instead be to create a constant pressure in the syringe, which would create a steady fluid flow through the needle.

It becomes apparent that a mechanical engineer would be useful here.