From graphene learned to make a flexible and durable thread

    Although graphene itself is a very strong material, using this strength at the macro level is not easy. Although there are options for using the mechanical properties of graphene in the form of flakes in the thickness of the material, which make it stronger, playing the role of “reinforcement”, the prospect of making fibers and threads from graphene from which it will be possible to make heavy-duty fabric or ropes with, moreover, looks much more interesting the same conductive properties.

    Scientists from the University of Pennsylvania and Shinshu University in Japan managed to make a thread from graphene oxide, comparable in strength to Kevlar, and at the same time very flexible and elastic, with a smooth surface and regular internal structure. Such threads can be easily twisted and knotted on them - this is a unique result, because all previous attempts gave, albeit strong, but stiff and brittle fibers. After annealing, as a result of which graphene oxide loses oxygen and turns into pure graphene, the filaments become more brittle, but acquire high electrical conductivity.



    The technology for making threads is quite simple. A suspension of graphene oxide flakes is poured onto a Teflon plate and smoothed to a uniform thickness using a Teflon bar and two strips of adhesive tape at the edges that specify the layer thickness. Then the suspension layer dries and a thin (2.9 μm) film of sticky flakes forms in its place. Long strips of such a film are then twisted into filaments with a thickness from a hundred micrometers to one and a half millimeters. The key point of this technology is that a completely dry film is curled into a thread, whereas in previous attempts, curling occurred when the film was not yet dry. The fact is that a film that has dried without tension has many fine wrinkles that remain in the thickness of the thread after twisting and play the role of "springs" that make the thread elastic.



    Various additives can be added to the initial graphene suspension, which change the properties of the filaments, for example, nylon fibers, which make the filaments softer and more flexible, or silver nanowires, which significantly increase the electrical conductivity of the filaments. After annealing at high temperature, the conductivity of such a silver-alloyed graphene filament is comparable to a copper wire, only the filament is much lighter and stronger.

    An article describing the technology and properties of the obtained filaments was published in the May issue of ACSNano magazine.


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