Tech Briefs Magazine - May 2022 - 38

Materials & Coatings
the polymer chains and the stiffer the
material. If there are only a few crosslinks,
the chains are longer and the material
is tough but too soft to be useful.
Researchers have resolved that conflict
and developed an elastomer that is
both stiff and tough. The team looked to
physical, rather than chemical bonds to
link the polymer chains. These physical
bonds, called entanglements, have been
known in the field for almost as long as
polymer science has existed but they've
been thought to only impact stiffness,
not toughness.
The researchers found that with enough
entanglements, a polymer could become
tough without compromising stiffness. To
create highly entangled polymers, the researchers
used a concentrated monomer
precursor solution with 10 times less water
than other polymer recipes.
By crowding all the monomers into
this solution with less water and then
polymerizing it, they forced them to
be entangled. Just like with knitted
fabrics, the polymers maintain their
connection with one another by being
physically intertwined. With hundreds
of these entanglements, just a handful
of chemical crosslinks are required to
keep the polymer stable.
As elastomers, the polymers have
high toughness, strength, and fatigue
resistance. When the polymers are submerged
in water to become hydrogels,
they have low friction and high wear resistance.
That high fatigued resistance and
high wear resistance increase the durability
and lifespan of the polymers.
For more information, contact Leah
Burrows at lburrows@seas.harvard.edu;
617-496-1351.
Developing Lightweight Glass for Efficient Cars and
Wind Turbines
A new machine learning model predicts the lightness and stiffness of glass compositions.
University of Michigan, Ann Arbor, MI
A
ll solid materials, including glass,
have a property called elastic stiffness
- also known as elastic modulus. It's a
measure of how much force per unit area
is needed to make the material bend or
stretch. If that change is elastic, the material
can totally recover its original shape
and size once that force is stopped.
Elastic stiffness is critical for any materials
in structural applications. Higher
stiffness means that it can sustain the
same force loading with a thinner material.
For example, the structural glass
in car windshields and in touch screens
on smartphones can be made thinner
and lighter if the glasses are stiffer. Glass
fiber composites are widely used lightweight
materials for cars, trucks, and
wind turbines.
Lighter, stiffer glass can enable wind
turbine blades to transfer wind power into
electricity more efficiently because less
wind power is " wasted " to make the blades
rotate. It can also enable longer wind turbine
blades, which can generate more
electricity under the same wind speed.
Because glasses are amorphous - or
disordered - materials, it is hard to predict
their atomistic structures and the
corresponding physical/chemical properties.
Computer simulations are used to
speed up the study of glasses but they require
extensive computing time, making
it impossible to investigate each possible
glass composition.
Researchers used existing high-through -
put computer simulations to generate
data on the densities and elastic stiff38
It's
hard to predict the properties of a glass from its composition because glasses are disordered
structures, as seen in this atom-level simulation. A new machine learning model can predict the
density and stiffness of glasses. (Photo: Qi Group)
nesses of various glasses. Then, they developed
a machine learning model that
is more suitable for a small amount of
data. The model was designed so that
it pays attention to the strength of the
interaction between atoms. In essence,
physics was used to give the model hints
about what was important in the data,
improving the quality of its predictions
for new compositions.
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While the machine learning model
was trained with glasses made of silicon
dioxide and one or two other additives,
it could accurately predict the lightness
and elastic stiffness of more complex
glasses, with more than 10 different
components. It can screen as many as
100,000 different compositions at once.
For more information, contact Kate
McAlpine at kmca@umich.edu; 734-763-2937.
Tech Briefs, May 2022
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Tech Briefs Magazine - May 2022

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