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Next generation rubber with self-healing properties |
| TheAllINeed.com |
(NC&T/CNRS) Working with readily-available small molecules of fatty acids, cleverly built into a network, the researchers created a material with rubber-like properties and capable of self-healing. The chemical company Arkema, partner in this research, is already developing products with industrial potential based on this technology.
Rubber is a soft material, capable of being stretched by 100 to 500% and then returning to its original shape with no noticeable change. This property is typical of macromolecular networks made up of long molecules (macromolecular chains) linked by strong bonds. A rubber tube can thus be considered to be a single, very large molecule.
One can thus imagine that molecules which can link to each other using hydrogen bonds, which are weak, can form networks (supramolecular networks). But previous research had shown that supramolecular networks made of small molecules form vitreous or semi-crystalline materials, which cannot withstand stretching or deformation. Furthermore, to form a network, di- or tri-topic molecules (molecules which can bond with two or three molecules respectively) were needed, and the process of synthesizing such molecules, making them compatible to mixing, and preventing the mixture from separating is generally quite an undertaking.
The researchers from the Matière molle et chimie laboratory(CNRS/ESPCI) used a mixture of small molecules from di- and tri-functional fatty acids with a variety of heteroatomic groups (amide, urea, N-carbamyl, imidazolidone), all capable of bonding together with hydrogen bonds. This structure was preferable to one made up of a single molecule, which would tend to form a crystalline structure. At room temperature, the resulting material behaves like rubber. At higher temperatures, (130-150°C) the material flows and can be shaped.
It was crucial for the researchers that the material be able to be reproduced, and they had as an additional constraint that it be made from simple raw materials. Their original approach uses mixtures of fatty acids with great availability and variety. The products are also vegetable-based (pine, sunflower, corn, canola) and thus non-toxic and renewable.
 | | Demonstration of the 4 stages of self-healing of rubber: damage to the structure, contact between severed bits, repair, stretching test. (Photo: © Laboratoire Matière molle et chimie (CNRS-ESPCI) |
Leibler's team also noticed that the design based on small molecules gave the material a very unusual property, namely that of spontaneous self-healing. Supramolecular rubber does not have adhesive properties, but the researchers noticed that after they were cut, the surfaces glued themselves back together if put in contact, without heating or applying strong pressure. Once repaired, the sample could again undergo considerable deformation (100 to 400%) before breaking. The process can be repeated several times, and, what is more surprising, the repairs can be performed several hours after the breaking.
Possible applications cover a number of fields, from building to high technology.
This research was carried out in close collaboration with the chemical company Arkema, which is currently developing products and materials with industrial potential based on these results.
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