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event yields novel emissions, reactions
Life Sciences Editor
photos to enlarge
by N. C. Eddingsaas & K. S. Suslick
phenomenon of mechanoluminescence was first discovered
in 1605 by Sir Frances Bacon from scratching sugar
with a knife. The top image is a photograph of the
mechanoluminescence of N-acetylanthranilic acid crystals
crushed between two transparent windows. The second
image is a photograph of the mechanoluminescence
of N-acetylanthranilic acid crystals in the shape
of the U. of I. logo crushed between
two transparent windows.
Researchers at the University of Illinois report that a new study of
mechanoluminescence revealed extensive atomic and molecular spectral
emission not previously seen in a mechanoluminescence event. The findings,
which appear online this month in the Journal of the American Chemical
Society, also include the first report of gas phase chemical reactions
resulting from a mechanoluminescence event.
Mechanoluminescence is light generated when a crystal, such as sugar
or quartz, is fractured by grinding, cleaving or via other mechanical
means. Sir Francis Bacon wrote about this phenomenon as early as 1605.
Others have used the effect to impress, if not enlighten, others.
“You may, when in the dark frighten simple people only by chewing
lumps of sugar, and, in the meantime, keeping your mouth open, which
will appear to them as if full of fire,” Father Giambattista Beccaria
wrote in “A Treatise Upon Artificial Electricity,” in 1753.
Scientists believe mechanoluminescence occurs as a result of the generation
of opposite charges along the fracture plane of an asymmetrical or impure
crystal. When the charges recombine the surrounding gas is ionized and
Mechanoluminescence that results from simple grinding or cleavage of
a crystal can be quite weak and difficult to study. Late last year,
U. of I. chemistry professor Kenneth Suslick and graduate student Nathan Eddingsaas reported
in the journal Nature that a new technique, the sonication of crystal
slurries, produced a much more intense mechanoluminescence than grinding.
Sonication, the use of sound energy to agitate particles or other substances,
causes high intensity collisions of crystal particles in liquid slurries.
The resulting mechanoluminescence is an order of magnitude brighter
than that produced by grinding.
Sonication of liquids causes acoustic cavitation: the formation, growth
and implosion of bubbles. This generates tremendous heat, pressure and
shockwaves within the liquid that can exceed the speed of sound. Crystal
particles suspended in a sonicated liquid collide and fracture, causing
The new study involved the sonication of a slurry of recorcinol (sugar)
crystals in the liquid paraffin, dodecane. When nitrogen or oxygen was
bubbled through the sonicated slurry, the resulting emission spectrum
was more than a thousand time more intense than that produced by grinding.
The researchers also saw emission lines not previously reported in a
mechanoluminescence event. These peaks on the mechanoluminescence spectra
are evidence of gas phase chemical reactions during the event.
“When oxygen is present, chemical reactions take place that are
similar to those that occur in the production of diamond films using
an electrical discharge,” Suslick said. “The intense mechanoluminescence
and chemical reactions produced by ultrasound give us a better understanding
of mechanoluminescence, mechanochemistry and the effect of ultrasound
on solids within a liquid.”
Editor’s note: To reach Kenneth Suslick,
call 217-333-2794; e-mail: email@example.com.