Here's an odd story. I heard it second-hand, so I'm not totally confident
of its accuracy. I have a call in to the originator.
A friend attended the 1995 ESD assn. symposium where a 3M engineer told of
an interesting phenomenon at a factory in the south. The humidity was
extremely high, yet when the guy entered the factory floor his
electrometer measured many tens of KV just inside the doorway. As part of
the production process they were taking two types of plastic film off an
enormous roll many feet long and spooling it onto two other rolls. The
dissimilar materials were generating opposite surface charges, so these
two rolls were acting as charge accumulators. The enormous rolls were
adjacent and oppositely charged throughout their volume, so the e-field
between them was incredibly high. They should form a capacitor, but an
unconventional one with non-conductive plates, and with the charges
trapped inside the plastic.
Here's the weird part. When workers tried to walk between the rolls, they
experienced a strong repulsion force. Repulsion, not attraction. When
the humidity was lower, they found that the field was so strong that they
were unable to push their way through!
Yet when one drops plastic fragments between oppositely charged parallel
plates, the fragments are sucked into the gap, rotate to align with the
field, and stick to one plate or the other. They are not *repelled!*
Anyone have an explanation of the odd phenomenon in the factory?
also:
Charging a film and spooling it up would be a neat way to create a
single-pole electret. After awhile it should "discharge" as opposite air
ions were attracted to its surface. But then you could peel a couple of
layers off and restore the original effect. I think VandeGraaff belts can
take tens of of microcoulombs per cm^2, so it wouldn't be hard to
accumulate a total charge in the millicoulomb range. I expect that air
breakdowns would impose the major limit. If you made a positive and a
negative "charge spool," the attractive force between them should be
amazing!
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