High-energy shape memory polymer could someday help robots flex their
muscles

Date:
September 8, 2021
Source:
American Chemical Society
Summary:
When stretched or deformed, shape memory polymers return to their
original shapes after heat or light is applied. These materials
show great promise for soft robotics, smart biomedical devices
and deployable space structures, but until now they haven't been
able to store enough energy. Now, researchers have developed a
shape memory polymer that stores almost six times more energy than
previous versions.



FULL STORY ==========================================================================
When stretched or deformed, shape memory polymers return to their
original shapes after heat or light is applied. These materials show
great promise for soft robotics, smart biomedical devices and deployable
space structures, but until now they haven't been able to store enough
energy. Now, researchers reporting in ACS Central Sciencehave developed
a shape memory polymer that stores almost six times more energy than
previous versions.


========================================================================== Shape memory polymers alternate between an original, undeformed state and
a secondary, deformed state. The deformed state is created by stretching
the polymer and is held in place by molecular changes, such as dynamic
bonding networks or strain-induced crystallization, that are reversed with
heat or light. The polymer then returns to its original state through
the release of stored entropic energy. But it's been challenging for
scientists to make these polymers perform energy-intensive tasks. Zhenan
Bao and colleagues wanted to develop a new type of shape memory polymer
that stretches into a stable, highly elongated state, allowing it to
release large amounts of energy when returning to its original state.

The researchers incorporated 4-,4'-methylene bisphenylurea units into
a poly (propylene glycol) polymer backbone. In the polymer's original
state, polymer chains were tangled and disordered. Stretching caused
the chains to align and form hydrogen bonds between urea groups,
creating supermolecular structures that stabilized the highly elongated
state. Heating caused the bonds to break and the polymer to contract to
its initial, disordered state.

In tests, the polymer could be stretched up to five times its original
length and store up to 17.9 J/g energy -- almost six times more energy
than previous shape memory polymers. The team demonstrated that the
stretched material could use this energy to lift objects 5,000 times
its own weight upon heating. They also made an artificial muscle by
attaching the pre-stretched polymer to the upper and lower arm of a wooden mannequin. When heated, the material contracted, causing the mannequin to
bend its arm at the elbow. In addition to its record-high energy density,
the shape memory polymer is also inexpensive (raw materials cost about
$11 per lb) and easy to make, the researchers say.

========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christopher B. Cooper, Shayla Nikzad, Hongping Yan, Yuto Ochiai,
Jian-
Cheng Lai, Zhiao Yu, Gan Chen, Jiheong Kang, and Zhenan Bao. High
Energy Density Shape Memory Polymers Using Strain-Induced
Supramolecular Nanostructures. ACS Cent. Sci., 2021 DOI:
10.1021/acscentsci.1c00829 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210908081516.htm

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