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There is a kind of "jelly" that won't break even if stepped on by an elephant (Photo: Unsplash) the main ingredient is water, so it must be as easy to be trampled and burst as a water balloon? Materials scientists don't throw in the towel.

If you want to make jelly, the most important raw material is water. A large basin of water, add a little jelly powder, can become a large basin of jelly.

However, the jelly made in this way is so fragile that it will break badly if you step on a few feet at will.

Ordinary jelly that has been crushed (photo: Popper stick) but now scientists at the University of Cambridge have developed a "super jelly" that, although the main ingredient is also water, will not break after being repeatedly run over by a car for more than 10 times. It is not only unbroken, but also can restore the original shape in a short time.

The team published the findings in the journal Nature Materials.

Come to the bucket. This "super jelly" is a kind of hydrogel, 80% of which is water. However, the secret to making water extremely tough is not jelly powder. Scientists used a substance called cucurbituril (cucurbituril).

Cucurbituril is a barrel-shaped molecule, which is aptly named because it is similar to gourd and pumpkin, both of which come from Cucurbitaceae.

To the right are cucurbituril [5] urea, cucurbituril [6] urea, cucurbit [7] urea and cucurbit [8] urea, all of which are barrel-shaped molecules (photo source: doi:10.1039 / D0RA04387G). These "buckets" are all connected by glycoluril units, five glycoluril units can be connected into cucurbit [5] urea, and six glycoluril units are connected into cucurbit [6] urea. However, no matter how many glycoluril units are used in the bucket, there is a cavity in the middle, which can be used to hold things. For example, the gourd [8] urea used by the team this time is a bucket that can hold two guest molecules.

When two "guests" enter the barrel, the chain polymers in which they are located cross-link each other to form a large network called supramolecular polymer network (SPN). Therefore, the gourd [8] urea, which is responsible for weaving the web, is also known as a "cross-linking agent".

When guest molecules enter the barrel, their polymer chains form a network called supramolecular polymer network (SPN) (photo: doi:10.1021 / acs.chemrev.5b00341). Water molecules are wrapped in a network like the one pictured above to form a hydrogel.

However, what the properties of the hydrogel will be depends on what the guest molecules in the bucket are. For many years, scientists have been fond of using cucurbituril to explore new materials, precisely because cucurbituril can bind to a variety of objects. Put in different objects, you will form different hydrogels, such as stretchable hydrogels, hydrogels that can quickly repair themselves, and so on.

Elephants will be fine if they step on it. This time, the first object chosen by the Cambridge team is perfluorophenyl, while the second object has multiple candidates (all phenyl substitutes).

Green indicates the first guest perfluorophenyl, purple indicates the second guest, and many substitutes of phenyl are candidates; grey barrel molecules represent cucurbit [8] urea; the reaction of guest and cucurbit [8] urea is reversible. (photo source: original paper) these guest molecules do not stay in the barrel all the time. The chemical reaction between them and the host molecule [8] urea is reversible and is in a dynamic equilibrium. In other words, "guests" come and go all the time.

The question is whether the "guests" walk fast or slowly. In the hydrogels made by scientists in the same way, most of the guest molecules dissociated quickly, and the resulting materials were soft and stretchable. But now, if the Cambridge team wants to make an "unbreakable" hydrogel, it has to choose the guest molecules that dissociate more slowly: the fast binding, the slow dissociation, and the large cross-linked network can maintain a tightly connected structure.

The left is the previous hydrogel research results, soft and stretchable; the right is the new research results, hard and compressible (photo source: original paper) the selected object, after meeting cucurbituril (subject), does bring the attribute that scientists expect: they stay in buckets for longer than the usual guest molecules. The resulting hydrogel will have a stronger structure to resist violent compression.

As mentioned above, the team chose only one first object for cucurbituril, while the second object tried many (from weak to strong compression performance). When one of the second objects enters the stage, the hydrogel formed is strong enough to withstand a pressure of up to 100 million Pascal. In this case, the hydrogel was compressed by 93%, so thin that it was about to become invisible from the photo, but it did not break. And after the heavy pressure disappears, it can return to its original shape in 2 minutes.

The top is before hydrogel compression, the middle is compression, and the bottom is less than 2 minutes after the end of compression (photo source: original paper). If you want to know what 100 million Pascal is, it is equivalent to a human pinky nail (1 square centimeter). Apply a heavy pressure of more than 1000 kilograms. Or to put it more figuratively, if an elephant stepped on a stamp-sized hydrogel with three feet in the air, the hydrogel would be safe and sound.

Now that there is "super jelly", it is obviously not enough to squash it once, and it will continue to be ravaged. The scientists let the car weigh 1200 kilograms, press one of the wheels (~ 300kg) on the hydrogel of 70 ×   50   ×   6mm for 1 minute, and then run it over it 16 times in a row. As a result, the hydrogel still lived up to expectations.

The top is a 6mm thick hydrogel before compression, and the bottom is a hydrogel that has been crushed many times by a car and restored to its original state (photo source: Cambridge University). It should be very soft, right? But according to the team, it is a hard hydrogel and the first known glassy hydrogel. Professor Oren Scherman, who led the study, also said that for years people have made rubber-like hydrogels, which are only half the picture; now, hydrogels with different compression properties, from rubber to glass, can be made, and the whole picture is complete.

What good will it do? First, scientists used Super Jelly to make a pressure sensor. Thanks to its excellent compression performance, this sensor not only measures a wide range (up to 2.5MPa), but also is very sensitive, and it can distinguish between standing, walking and jumping in real time if placed on the soles of your feet.

The pressure data output by the capacitive pressure sensor, left for walking, middle for jumping, and right for station (picture source: original paper), this small demonstration experiment shows that it is possible for "super jelly" to be applied in the field of bioelectronics.

In addition to being suitable for sensors, the property that withstands great pressure without breaking may have other uses. Its compressive strength (compressive strength) is at least one order of magnitude higher than that of bovine articular cartilage. Therefore, when human cartilage is injured and degraded, "super jelly" may become a replacement material.

Scientists also hope that one day these new materials will have the opportunity to use their talents in artificial muscles, artificial limbs or soft robots.

However, it is not edible.

Original paper:

Https://www.nature.com/articles/s41563-021-01124-x

Reference link:

Https://pubs.acs.org/doi/10.1021/acs.chemrev.5b00341

Https://www.eurekalert.org/news-releases/935677

Https://www.newscientist.com/article/2299038-soft-yet-strong-gel-keeps-its-shape-after-being-run-over-by-a-car/

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by: chestnut, revision: Clefable

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