New material offers remarkable combo of toughness and stretchiness


Date:
February 21, 2022
Source:
North Carolina State University
Summary:
Researchers have created new materials that are very stretchable
and extremely tough. The new materials fall under the broader
category of ionogels, which are polymer networks that contain
salts that are liquid at room temperature.



FULL STORY ========================================================================== Researchers have created new materials that are very stretchable and
extremely tough.


========================================================================== "Materials that can be deformed, but that are difficult to break or tear,
are desirable," says Michael Dickey, co-corresponding author of a paper
on the work and the Camille & Henry Dreyfus Professor of Chemical and Biomolecular Engineering at North Carolina State University. "Nature is
good at this; think of cartilage as an example. But engineering synthetic materials with these properties has been difficult, which makes our work
here exciting." The new materials fall under the broader category of
ionogels, which are polymer networks that contain salts that are liquid
at room temperature. These salts are called ionic liquids.

Dickey and his collaborators have made ionogels that are nearly 70%
liquid, but have remarkable mechanical properties. Namely, they're
tough -- meaning they can dissipate a lot of energy when you deform
them, making them very difficult to break. They're also easy to make,
easy to process, and you can 3D print them.

"Hydrogels, which are polymer networks that contain water, are fairly
common," Dickey says. "For example, contact lenses are hydrogels. But
ionogels have some advantages over hydrogels. Ionic liquids don't
evaporate like water, so you don't have to worry about the ionogels drying
out. Ionogels are also electrically and thermally stable and conduct electricity well, raising some interesting opportunities for future applications." To make the new ionogels, the researchers started with
monomers of polyacrylic acid (used in baby diapers) and polyacrylamide
(used in contact lenses) and copolymerized them in a solution of ionic
liquid using ultraviolet light. In other words, they took the ingredients
for polyacrylic acid and polyacrylamide, placed them in an ionic liquid,
and shone light on it to create a copolymer that incorporates both
monomers and the ionic liquid itself.

"The end result is significantly better than an average of the two
materials," Dickey says. "It is like adding 1+1 and getting 10. The
resulting gel has the stretchability of polyacrylic acid and is even
stronger than the polyacrylamide. In terms of toughness, it's better
than cartilage. But the differences between ionogels and hydrogels
make them advantageous for different applications." In addition,
the ionogels created by Dickey's team also have self-healing and shape
memory properties. You can stick two pieces of the ionogel together,
expose it to heat, and it reforms a strong bond. By the same token, you
can deform the ionogel into a temporary new shape, but it will return
to its original shape when exposed to heat. The amount of heat needed
depends on how quickly you want the material to "heal" or return to
its normal shape. When exposed to a temperature of 60 degrees Celsius,
the actions only take tens of seconds.

"We're excited that we've made something with truly remarkable properties
that can be made very easily -- you just shine light on it -- using widely available polymers," Dickey says. "And you can tailor the properties
of the ionogels by controlling the ratio of ingredients during the copolymerization process.

"We're already working with one industry partner, and are open
to working with others to develop applications for this new breed
of ionogels." Video of the ionogels: https://youtu.be/SoAxmv7I9KA ========================================================================== Story Source: Materials provided by
North_Carolina_State_University. Original written by Matt Shipman. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Meixiang Wang, Pengyao Zhang, Mohammad Shamsi, Jacob L. Thelen,
Wen Qian,
Vi Khanh Truong, Jinwoo Ma, Jian Hu, Michael D. Dickey. Tough and
stretchable ionogels by in situ phase separation. Nature Materials,
2022; DOI: 10.1038/s41563-022-01195-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220221115416.htm

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