I am looking for chemicals, dyes, or any materials that have a
piezochromic behavior.  That is, they will change color when pressure
is applied. This might also be referred to as mechanoluminescence.  I
have seen some articles that describe piezochromism but only in high
pressure experiments.  I am interested in chemicals or materials that
exhibit a piezochromic effect under low pressure.  Is this color
change temporary or permanent?  Is it a bold color change that can be
readily observed or more subtle?

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Clarification of Question by seekwisdom-ga on 16 Dec 2002 16:35 PST

Are there any chemicals, dyes, or materials that have a piezochromic
behavior.  That is, they will change color when pressure is applied. 
I am looking for something that works similar to thermochromic inks or
dyes, or like liquid crystals, but the change is due to pressure and
not heat. This might also be referred to as mechanoluminescence. I
have seen some articles that describe piezochromism but only in high
pressure experiments.  I am interested in chemicals or materials that
exhibit a piezochromic effect under low pressure.  Is this color
change temporary or permanent?  Is it a bold color change that can be
readily observed or more subtle?

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Request for Question Clarification by alienintelligence-ga on 01 Jan 2003 22:40 PST

Hi seekwisdom,

Were you still looking for an 
answer to your question regarding
piezochromic substances? If so,
could you please state a sample
pressure range for the substance
to react to? Will there be an
implied temperature range? How 
big (surface area/volume) are
we considering? 

thanks
-Alien

seekwisdom,
not sure if you are barking up the right tree, becos your question
itself is innate with a lot of assumptions that you might not have
thought through.
(1) any substance (if there is such a substance) that exhibits
piezochromism under low pressure would neccessary imply that it is
unstable under normal conditions. i.e. any changes in pressure causes
an impact to the integrity of the substance.
(2) have you considered looking into combinatorial gemstones or rock
material like OPAL?  I think diamonds under certain kinds of pressure
would collapse into graphite (i.e. change from great ability to
refract light to absorb light this change is considered quite
"permanent" as the cost to convert graphite back to diamonds would be
exorbitant - but i guess this is the opposite of what you are looking
for 8-)
(3) My next best advice is for it to consider a microorganic approach
(i.e. a process which is biochemical), I am guessing you are looking
for some means to measure minor pressure changes using a simple dye
display. There would be ways which we could enclose microorganisms
within pads (pressure sensors) that has some simple chemical dye, so
when the microbes react to a touch or other things, they could release
some chemicals to interact with the dyes to change its coloration. 
(potentially reversible).

A friend and I did some experiments with piezoelectric materials and
colors of polarization in high school.  Crude stuff but not too far
from the phenomenon behind color LCDs.  Is that in the ballpark of
what you are after?

-- mathtalk-ga