1. Results
What
Is
Shape
Memory
?
Mo4va4on
And
Objec4ve
Previous
studies
of
the
shape
memory
effect
have
been
focused
on
macro-­‐scale
(bulk)
materials.
Recently
people
have
demonstrated
shape
memory
of
2-­‐D
sub-­‐micron
surface
paHerns
however,
no
one
has
inves4gated
the
ability
of
micro
scale
polymer
structures
to
remember
a
shape
aLer
large
3-­‐D
deforma4ons.
Therefore,
the
project
goal
is
to:
• Create
the
world’s
first
shape
memory
micro-­‐
par4cle
Within
a
typical
shape
memory
cycle,
polymer
networks
are
deformed
into
a
temporary
shape
then
brought
back
to
their
original
shape.
In
the
permanent
shape
(top
picture),
polymer
chains
between
the
crosslinking
points
(black
dots)
are
in
a
low
energy
state.
When
a
mechanical
loading
is
applied
to
a
rubbery
polymer,
the
polymer
is
deformed
into
a
higher
energy
state
(blue
picture).
This
deformed
shape
can
be
maintained
if
the
polymer
is
cooled
down
into
a
glassy
state,
and
will
remain
there
even
aLer
the
load
is
removed.
Upon
hea4ng
the
polymer
back
to
a
rubber,
the
shape
memory
polymers
will
recover
their
original
low
energy
shape.
In
general,
cross-­‐linked
polymers
are
oLen
known
as
shape
memory
polymers
and
can
be
deformed
into
a
variety
of
shapes;
yet
exhibit
the
ability
to
return
to
their
permanent,
low
energy
shape
through
s4mula4on
by
an
external
s4mulus
such
as
temperature
change.
0
0.5
1
1.5
2
2.5
3
3.5
4
Original
Shape
Compressed
Constrained
Recovery
Unconstrained
Recovery
Micrometers
Shape
memory
was
aCained!
Original
Shape
Compressed
Unconstrained
Recovery
Constrained
Recovery
What
Is
A
Polymer?
End
to
End
Distance
Probability
Polymers
are
long-­‐chain
macromolecules
that
consists
of
repea4ng
structural
units
with
very
high
molecular
weight
that
are
created
through
polymeriza4on.
ΔG=ΔH-­‐TΔS
Polymer
chains
have
a
preferred
end
to
end
distance,
which
allows
them
the
greatest
number
of
conforma4ons
(highest
amount
of
entropy),
as
indicated
in
the
middle
chain.
Chains
with
a
shorter
end
to
end
distances
(farthest
leL)
have
a
greater
tendency
to
expand,
whereas
chains
with
longer
end
to
end
distances
(rightmost)
have
a
greater
tendency
to
contract.
Shape
Memory
Micropar4cles
Adora
Yabut,
Lewis
Cox,
Yifu
Ding
University
of
Colorado
Boulder
Conclusion
• Micropar4cles
were
exposed
to
extremely
large
3-­‐D
deforma4ons,
and
held
in
the
temporary
shape.
Upon
hea4ng,
recovery
of
deformed
par4cles
was
confined
by
the
substrate.
ALer
removing
them
from
the
substrate
we
observed
full
recovery
of
the
original
shape,
thus
demonstra4ng
for
the
first
4me
the
concept
of
shape
memory
micro-­‐par4cles.
Acknowledgements
This
project
was
made
possible
by
the
YOU’RE@CU
seminar
held
by
Virginia
Ferguson
and
Beverly
Louie.
Methods
and
Experimental
Apparatus
Dipped
a
flat
silicon
wafer
into
a
aqueous
solu4on
containing
polystyrene
micro-­‐par4cles.
Using
an
op4cal
microscope,
the
par4cles
were
confirmed
to
have
been
deposited
onto
the
wafer.
The
deposited
par4cles
were
deformed
into
a
flaHened
shape
by
using
a
nanoimprinter.
A
second
piece
of
silicon
with
a
treated
surface
to
reduce
adhesion
was
placed
on
top
of
the
deposited
par4cles,
and
the
two
plates
were
placed
within
the
imprinter.
The
environment
was
then
heated
to
120°C
(significantly
above
the
glass
transi4on
temperature
of
polystyrene:
95°C)
and
the
par4cles
were
allowed
to
equilibrate
for
3
minutes.
A
pressure
of
15
bar
was
then
applied
for
5
minutes
to
mold
the
par4cles
into
a
temporary
shape.
With
the
15
bar
pressure
s4ll
being
applied,
the
par4cles
were
then
cooled
back
down
to
35°C
(temperature
below
Tg)
in
order
to
freeze
the
polymer
chains
in
a
glassy
state
and
lock
in
the
deformed
temporary
shape.
ALer
performing
the
compression,
the
par4cles
were
observed
with
an
op4cal
microscope
to
confirm
deforma4on.
A
por4on
of
the
compressed
par4cles
were
then
placed
on
a
hot
stage
at
120°C
for
2
minutes
to
heat
them
back
above
their
Tg
and
induce
the
shape
recovery.
Atomic
Force
Microscopy
(AFM)
consists
of
a
can4lever
with
a
sharp
4p
that
is
used
to
scan
the
par4cle
on
the
surface.
The
AFM
was
used
to
accurately
measure
the
par4cle
heights
at
each
step
of
the
experiment.
Scanning
Electron
Microscope
(SEM))
is
a
microscope
that
produces
images
by
capture
scaHered
electrons
instead
of
light.
The
SEM
provided
us
with
high
resolu4on
pictures
of
par4cles.