MadSci Network: Engineering

Re: Whar determines the size of a droplet from a pipette and are all the same

Date: Thu Nov 28 08:01:04 2002
Posted By: Werner Sieber, Research Scientist, Coating Effects,
Area of science: Engineering
ID: 1021320114.Eg

Dear Louanna,
You are quite right with your contention that there are big drops and 
little drops. (I'm not discussing drops sitting on a surface here - that's 
even more complicated) The size of a drop depends not only on properties 
intrinsic to the liquid at hand (surface/interface tension, density) but 
also on its adhesion to the rim of the dropper or other orifice from which 
it emerges. If an injection needle is used, this tends to yield smaller 
drops than a medicine dropper.
Most drops are generated under dynamic conditions (i.e. ejected more or 
less violently). This causes premature detachment from the nozzle. Drops 
as small as 3 picoliters (millionths of a microliter) can thus be 
generated by the printhead of an ink jet printer. On the other end, out in 
gravity-free space, drops of unlimited size are theoretically possible, if 
you spend enough time growing them.
Best Regards
Werner Sieber

P.S. I have tried severel times to answer this question since June, but 
the line was apparently down.

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