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Re: supercaps



Oops! Apparently I had not finished reading Ludwik's post about his supercap.
(I must have thought the message was over at the paragraph break after his
point 1 which lined up with a viewing screen page break.) Upon re-reading his
(entire) post it is apparent that he does see hysteresis as well as a
"rebound" effect. This is substantially more complicated than just the
nonlinear dQ/dV relationship that I had thought he was reporting.
Nevertheless it is possible that such effects still do not indicate chemical
reactions. It is possible that the dielectric is irreversibly more sluggish
in depolarizing than polarizing do to a lattice effect. The polarized
orientation of the molecules may take longer to randomize due to the presence
of similarly orientated molecules that are neighbors. The steric effects of
the interaction between neighboring molecules may inhibit "orientational
melting". It is also may be possible that the dielectric is a ferroelectric
substance with a spontaneous polarization. When the supercap is discharged
the dielectric is broken up into many domains whose polarizations cancel out
on a large scale (like a piece of unmagnetized iron). As the supercap is
charged these domains align their polarizations with the prevailing electric
field from the charged electrodes. When the supercap is discharged it may
take a while for these domains to spontaneously misalign wrt each other. I
think this may explain both the rebound effect as well as the hysteresis.
There may also be some irreversibility in the mechanical properties of the
dielectric as well. The work done on the dielectric in compressing it to a
given state of strain may be less than the work it does on its environment as
it is unloaded. Such an effect could also explain some of the irreversibility
in the nonlinearity charge/discharge Q vs. V function.

David Bowman
dbowman@gtc.georgetown.ky.us