Plastics aren't what we think. New study finds they're a tad rubbery,
paving the way for better products

Date:
August 18, 2021
Source:
University of South Florida (USF Innovation)
Summary:
A breakthrough could pave the way for better products, such as
improved batteries, automobile paint and cellphone screens.



FULL STORY ==========================================================================
A breakthrough by researchers at the University of South Florida (USF)
and collaborating institutions around the world could pave the way
for better products, such as improved batteries, automobile paint and
cellphone screens.


==========================================================================
When you zoom in on many modern materials, such as those in some of the
newest batteries that are made with glassy polymers -- which include
many plastics - - they don't appear uniform. Instead, they look like a
tie-dyed shirt, with swirls of different materials. According to the researchers, this "nanoscale structure" can yield such extraordinary
properties because the surface of glassy polymers isn't hard, but rather
has a rubbery consistency.

A new study published in Nature is reshaping how we understand the
behavior of glass, which is a state of matter that combines aspects of
solid and liquid.

Researchers at USF, together with collaborators at Princeton University
and Zhejiang Sci-Tech University, discovered that a natural effect occurs
at the surface of glassy polymers, creating a compliant rubbery layer
only a few dozen atoms thick that has properties completely different
from the rest of the material. This behavior has widespread technological implications, revealing how glassy polymers can adhere to each other and potentially providing insight into scratch resistance at the molecular
level.

"This gives us the ability to understand and control how glassy polymers -
- plastics -- behave right at their surface," said corresponding author
David Simmons, associate professor of chemical, biological and materials engineering at USF. "Whether it's a particle of dust sticking to paint,
two fibers sticking together in a 3D printer, or abrasion at the surface
of a pair of a plastic lens in your glasses, this microscopic layer at the surface of plastics is immensely important to how these materials perform,
and now we really understand its nature for the first time." Simmons and
his collaborators made this discovery by forming "wetting ridges," tiny
ridges at the surface of a plastic, by releasing an ionic liquid droplet
on polystyrene surfaces at various temperatures. Polystyrene is a solid plastic, a type of glass, that's naturally clear and often used for
food packaging, consumer products and building materials. Through these measurements and by zooming in to the molecular scale with supercomputer simulation models, they revealed the presence of this soft, rubbery layer
and how it can be controlled. This breakthrough could point to finding
the "sweet spot" for important properties such as adhesion and scratch resistance, even on rigid surfaces.

The theory is similar to the modern understanding of what makes
ice skating possible. The top molecular layer of the rink acts like
water, even when the rink is frozen, allowing skates to glide over the
surface. Otherwise, it wouldn't be possible.

========================================================================== Story Source: Materials provided by University_of_South_Florida_(USF_Innovation). Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Zhiwei Hao, Asieh Ghanekarade, Ningtao Zhu, Katelyn Randazzo,
Daisuke
Kawaguchi, Keiji Tanaka, Xinping Wang, David S. Simmons, Rodney D.

Priestley, Biao Zuo. Mobility gradients yield rubbery surfaces
on top of polymer glasses. Nature, 2021; 596 (7872): 372 DOI:
10.1038/s41586-021- 03733-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818130558.htm

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