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Will
the ferrofluid keep its magnetic properties even when dried out?
Yes,
the ferrofluid will dry and the dried fluid retains its magnetic
properties. I have a piece of filter paper, which I used to filter
some of the fluid over a year ago and it still responds to a magnet.
I would just mention that ferrofluid responds to magnets. It does
not retain magnetism after the magnet is removed. This applies to
the fluid and to the dried film.
Is
there anything I can add to the ferrofluid that WILL NOT mix with
it? Basically, I was hoping to put some
ferrofluid
in a clear container along with water and the two won't mix.
No,
water will not mix with the ferrofluid. The ferrofluid is heavier
than water so will be the bottom layer. If you need the ferrofluid
to be the top layer you will need to thin it a little with kerosene
or something similar to it.
What
size are the particles in the ferrofluid
The
particles within the ferrofluid are approximately ten nanometres. A
nanometre is approximately one billionth (10-9)
of a meter, so is pretty small.
Whenever
the ferrofluid touches the sides of a container it leaves a fine
film behind. Is there any way I can
stop
this from happening? Is there any material or coating I can apply to
the inside of the container to stop the fluid sticking to the sides,
a sort of wax or polymer based coating perhaps?
This
is a problem in working with ferrofluid. It does coat most things.
If you are going to find something it will not stick to, I would
suggest something very hydrophilic (having an affinity for water)
to repel it. Wax or similar will only make it worse. We have always
worked on the basis of setting up the experiment then leaving it to
settle before starting. If your experiment is not amendable to this
regime, the only other suggestion I can make is to use water based
ferrofluid, which is much cleaner than the solvent based.
Is
there anything (such as a dye), which can be added to the ferrofluid
to change the colour? It would be interesting to try and give the
ferrofluid a brighter and more aesthetically appealing colour?
The problem is the fluid is so intensely coloured to
begin with, so it would be difficult for a dye to show through.
Unfortunately, a pigment would not work because as soon as you place
the fluid near a magnet, the pigment would be rejected and the
mixture of the two would separate. The best option would be a very
intense fluorescent dye dissolved in the solvent phase of the fluid.
Alternatively, you could try a pigment or fluorescent dye in the
water based ferrofluid then maybe try illuminating the fluid with a
UV light. Alternatively, for solvent based fluid, you would need oil
soluble fluorescein.
Could
you give me some ideas of what I can use the ferrofluid for? Do you
know of any interesting
experiments
that I can play with?
In
industry, ferrofluid is used to make pressure seals and as a coolant
in high quality speaker systems. One experiment you might like to
try is to make a sink/float separator. Take two strong magnets and
fix them to be about a centimetre apart, attracting each other. You
will need to fix them strongly so they do not meet as there is a
danger they could shatter. Put some ferrofluid into the space
between the magnets and it will form a plug of fluid. Because the
fluid is attracted to the magnets it will try to occupy all of the
space and if you introduce anything non-magnetic into the space it
will be repelled. If the substance is light, like aluminium, it will
float on top, even though the metal is denser than the fluid and
would normally sink. If you use a heavier metal like lead, it will
overcome the repulsion and sink through. In this way you can make a
simple sink/float separator.
Here's
an interesting one to think about. Take a piece of glass tube and
place this in the gab between the magnets. Introduce the fluid into
the tube to form a plug. This plug will seal the tube and you can
float a head of water on top of it. Thread a line through the plug.
Attach a float to the line and pull it up through the seal. Once the
float is in the water, it will float up and in theory it could pull
up another float. Join them in a circle and you may find you have a
perpetual motion machine.
Is
ferrofluid stable under water indefinitely? I am conducting an
experiment where I am attempting to keep the water in a constant
motion (sort of like a lava lamp) without using a visible agitator.
I am toying with the idea of using ferrofluid instead of a magnetic
stirring bar. Do you think that would work?
Ferrofluid
is stable long term under water although, you may notice a slight
oil film. Ferrofluid will follow a moving magnet in the same way
that a stirring bar does. It has a much weaker saturation
magnetisation than steel, so the effect may not be as strong. If you
want to use ferrofluid as the actual lava lamp medium, you would
need to add some salt to the water phase to increase its density
until the ferrofluid floats on top. Then you could use a pulsing
electromagnet to draw the fluid down.
I
wondered whether you knew anything about the magnetorheological
properties of your ferrofluid (i.e. how
much
the viscosity increases in the presence of a saturating magnetic
field). I am aware that normally fluids with bigger magnetic
particles are used for this general application but for my specific
task the small particle size is attractive.
Ferrofluid
is strange stuff. One of the strange things about it is that it
continues stiffening beyond its saturation magnetisation. The oil
based fluid we supply has a saturation magnetisation of 160 gauss
but continues stiffening up to about 1 tesla and for all I know,
beyond. In the end it stiffens enough to support lead or gold. I
know this is a function of pseudo density rather than viscosity but
I hope it will be helpful. In the absence of a magnetic field the
fluid is water thin.
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