Supramolecular adhesive with usable temperature range of 400 degrees Celsius
Researchers have developed a supramolecular adhesive that is
recyclable and has outstanding gluing properties across a wide range of
temperatures, from liquid nitrogen (−196 °C or ca. −320 °F) up to oven-hot temperatures
(200 °C or ca. 400 °F). As the team report in the journal Angewandte Chemie, the adhesive got its efficiency from an exceptionally tight interlocking of the molecular components during curing.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Unlike standard adhesives, supramolecular adhesives do not create
adhesion by the molecular components crosslinking with one another.
Instead, they form a tight-knit self-assembly during curing, like puzzle
pieces fitting together. Researchers are interested in such
supramolecular systems because they offer sustainability and
customizability and, in principle, the individual starting materials can
be recovered again and their chemical behavior can be tailored.
However, to date, the performance of such glues has been decent at best,
not to mention highly dependent on environmental conditions.
The new supramolecular glue, developed by a research team headed by
Kai Liu from Tsinghua University, Beijing, China, consists of two
components, one of which is a small protein that is synthesized in
bacteria modified for the purpose. The other component is a crown
ether—a ring-shaped molecule which can wrap snugly around another
molecule, much like a crown sitting on a queen’s head.
The researchers observed this snug interaction between the molecules
in their adhesive system. By adding the crown ether and the protein
together and heating the solution for curing, the crown ether became
anchored to the surface of the protein. The team noted that the protein
and crown ether were so tightly bound to each other by their opposing
charges and other molecular interactions that they formed a new,
interlocking structure, which “welded” the proteins together.
The result was an extraordinarily strong adhesive effect. Steel
plates glued together withstood high shear forces at room temperature,
in liquid nitrogen, and at 200 °C. The adhesive worked for different
materials, and under water as well. Such a broad spectrum of working
conditions is seldom achieved, even with specialist adhesives, and is
certainly a first for supramolecular adhesives. Promisingly, the
interlocking components could be broken apart and recycled again, and
the reused adhesive lost virtually none of its power.
The researchers believe that one reason for this exceptional adhesive
effect, particularly at low temperatures, is a result of the specific
supramolecular interactions at play. In particular, the tight
interlocking of the components drove water out of the protein. This
meant that no ice crystals were able to form when frozen—as in
antifreeze—which in many conventional glues would lead to premature
cracking.
The researchers suggest that this new adhesive could be applied to
the manufacture of special parts that will be subject to greatly
fluctuating conditions during use; for example, the wide temperature
ranges to which spacecraft are exposed.
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About the Author
Dr. Kai Liu is a
professor in the department of chemistry at Tsinghua University,
Beijing, China. He heads a laboratory performing research at the
interface of biotechnology, biosynthetic materials, and information
technology.