Harvard creates beautiful,
The beautiful flowers that you see
above, and dotted throughout the
rest of this story, are around 25
micrometers tall and 10
micrometers wide.
A strand of
human hair, in comparison, is around
100 micrometers thick. Even more
impressively, these flowers self-
assembled from three normal
chemical compounds. Rather than
just an exercise in aesthetics,
though, scientists hope these
nanoflowers can improve our
scientific understanding of how
immensely complex structures in
nature, such as human embryos,
self-assemble.
To create the flowers, scientists at
Harvard start by dissolving barium
chloride and sodium silicate into a
beaker of water. At the bottom of
the beaker, there’s a glass slide or
metal blade. Then, without any kind
of input from the scientists, carbon
dioxide from the air starts to
dissolve in the clear solution,
starting a reaction that creates
white barium carbonate crystals. As
part of this chemical reaction, an
acid is released into the area
immediately surrounding the barium
carbonate, lowering the local pH and
preventing the creation of more
barium carbonate. The dissolved
sodium silicate, triggered by the
acidic environment, jumps into
action, coating the barium carbonate
with a layer of silica and using up
the acid. The process then starts
again from the beginning.
Now, what the scientists have
discovered, is that the self-assembly
process can be very finely controlled
by varying the concentration of
carbon dioxide, pH of the solution,
and temperature. Increasing the
amount of carbon dioxide, for
example, creates broad-leafed
structures.
By exactly controlling the
environment for a few hours, it’s
possible to build nanoflowers — or
indeed, probably many other shapes
as well. We should probably note at
this point that these pictures are
false-color scanning electron
microscope images; in reality, the
flowers are white. (Though,
considering they’re smaller than the
eye can see, the color probably
doesn’t matter.)
As for why these flowers are
actually an important scientific
breakthrough, you need only look at
nature, where self-assembly rules
supreme. It is due to local chemical
gradients — differences in pH, or
signaling molecules emitted from
living cells — that incredibly
complex structures arise. This
knowledge might allow us to meddle
with existing self-assembled
systems, to create weird and
wonderful Frankensteins, but the
more likely scenario is that we will
use it to inspire our own, human-
made, biomimetic self-assembled
materials. After all, when you’re
working on chips or materials that
have nanometer-scale features, self-
assembly is really the only viable
route towards commercial scale
production.
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