Immiscible Fluids in Weightlessness

name         Justin
status       educator
grade        9-12
location     IL

Question -   I am preparing lessons about density.  I have used
a density column in the past (as described at this site).  In
researching about immiscible fluids (so that I can mix the column
and have it all settle back out), I began wondering how this would
work in a weightless environment.

Do nonmiscible fluids mix uniformly in a weightless environment?  If
they separate, what does the geometry look like?  Water and oil
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Justin,

The reason that two liquids are immiscible in the first place is not 
because of density, but because the polarity of the solvents are too 
different.  The saying goes, "like dissolves like" and this means 
that solvents that have similar polarity will be miscible with each 
other and solvents with dissimilar polarities will be immiscible 
with each other.  Gravity comes into play as a way to usefully 
separate two immiscible fluids, as the heavier one (more dense) will 
sink to the bottom.  Taking gravity away will not change the fact 
that two liquids are immiscible, it just means that now the heavier 
one will not sink, it will disperse into globs of one solvent and 
globs of another solvent.  The direction of the forces that separate 
the two immiscible liquids will determine the direction that a 
particular globule of solvent will travel, since there is no gravity 
to overwhelm this force.  One thing that you could do to separate 
two immiscible liquids in space is stick them in a bucket and swing 
the bucket around.  The applied centripetal force will act like 
gravity, forcing the heavier liquid to the bottom of the bucket.

Matt Voss
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I wish I could give you a simple answer to the behavior of 
immiscible fluids in zero gravity, but to my knowledge there is not 
one. The behavior of fluids in zero gravity is complicated because 
factors that are overwhelmed in a gravitational field become 
important and dominant when the gravitational field is not present.
   The best lead I can give you is a "Google search" on the terms: 
'immiscible liquids zero gravity'. This will lead you to many 
references. The bottom line is that the behavior is complicated!!!

Vince Calder
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