Momentum - The Magazine for Virginia Tech Mechanical Engineering Vol. 3 No. 3 Fall 2018 | Page 27

Zheng, also an affiliated faculty member of
the Macromolecules Innovation Institute, has
received grants to study nanoscale materials
and scale them up to lightweight and func-
tional materials for applications in aerospace,
automobiles, and batteries.
Previously, researchers could print graphene
using an extrusion process, sort of like squeez-
ing toothpaste, but that technique could only
create simple objects that stacked on top of
itself.
“With that technique, there’s very limited
structures you can create because there’s no
support and the resolution is quite limited, so
you can’t get freeform factors,” Zheng said.
“What we did was to get these graphene layers
to be architected into any shape that you want
with high resolution.”
This project began three years ago when
Ryan Hensleigh, lead author of the article and
now a third-year Macromolecular Science and
Engineering Ph.D. student, began an intern-
ship at the Lawrence Livermore National Lab-
oratory in Livermore, California. Hensleigh
started working with Zheng, who was then
a member of the technical staff at Lawrence
Livermore National Laboratory. When Zheng
joined the faculty at Virginia Tech in 2016,
Hensleigh followed as a student and continued
working on this project.
To create these complex structures, Hens-
leigh started with graphene oxide, a precursor
to graphene, crosslinking the sheets to form
a porous hydrogel. Breaking the graphene
oxide hydrogel with ultrasound and adding
light-sensitive acrylate polymers, Hensleigh
could use projection micro-stereolithography
to create the desired solid 3D structure with
the graphene oxide trapped in the long, rigid
chains of acrylate polymer. Finally, Hensleigh
would place the 3D structure in a furnace to
burn off the polymers and fuse the
object together, leaving behind a pure
and lightweight graphene aerogel.
“It’s a significant breakthrough
compared to what’s been done,”
Hensleigh said. “We can access pretty
much any desired structure you
want.”
The key finding of this work,
which was recently published with
collaborators at Lawrence Liver-
more National Laboratory in the
journal Materials Horizons, is that
the researchers created graphene
structures with a resolution an order
of magnitude finer than ever printed.
Hensleigh said other processes could
print down to 100 microns, but the
new technique allows him to print
down to 10 microns in resolution,
which approaches the size of actual
graphene sheets.
Above: Zoomed-in scanning electron microscope
picture of a graphene octet-truss at a resolution of 1
micrometer.
Below: Zoomed-in scanning electron microscope
picture of a graphene octet-truss at a resolution of 10
micrometers.
“We’ve been able to show you can
make a complex, three-dimensional
architecture of graphene while still
preserving some of its intrinsic prime
properties,” Zheng said. “Usually
when you try to 3D print graphene
or scale up, you lose most of their lucrative
mechanical properties found in its single sheet
form.”
Co-authors include Huachen Cui, a doctoral
student in Zheng’s lab, and six people from
Lawrence Livermore National Laboratory –
James Oakdale, Jianchao Ye, Patrick Campbell,
Eric Duoss, Christopher Spadaccini, and
Marcus Worsley. Zheng and Hensleigh are
funded by an Air Force Young Investigator
Award (Dr. Jaimie S. Tiley) and the National
Science Foundation.
MOMENTUM
FALL 2018
PAGE 27