It has been the dream of many a polymer chemist, especially those within the textile industry, to have the chance of creating a fabric that is formed from bottom-up approaches. Until now, many have tried but failed, to produce a self-assembly reaction with interwoven one-dimensional fibers (one molecule thick) to produce 2-dimensional (2D) planar sheets of textile.
An international team of researchers has now made this dream a reality. The team have managed to produce an innovative strategy to fabricate 2D polymers that consist of interwoven polymer fibers, held together by the interlocking mechanical forces that arise from the weaved pattern.
Textiles are used in everyday life, and in vast quantities. Current textile production methods typically employ a top-down approach. The formation of one-dimensional (1D) fibers was a big stepping stone for the textile industry that allowed for mass production of fabrics. 2D polymers have previously been created, alongside other 2D materials such as graphene, but most require harsh conditions- not an ideal situation for fabric production.
Textiles in themselves are different to standard polymer networks. Within pure 2D polymer networks, the cross-links and interlinking of different polymer chains is due to covalent bonding between the fibers- a chemical approach. Whereas, textiles are not chemically bonded to each other, but are mechanically interlocked. The different interlocking fibers in textiles are instead held in place by weak intermolecular forces. This way of interacting is necessary for textiles, as it allows for flexibility compared to other 2D networks.
Like many industries today, there is an effort to try and shift the production process from top-down methods to bottom-up methods; as there is a much greater production potential, control and specificity that can be produced using bottom-up methods, once they have been optimised.
The 2D textiles produced are a sophisticated mixture of quadritopic linkers and a metal-organic framework (MOF)- a hybrid organic-inorganic porous material. The quadritopic linkers are sandwiched between sacrificial MOF thin films to form a multi-heteroepitaxial crystalline system. The fabrication method involved a layer-by-layer (LbL) approach to produce a crystalline coordination network using liquid-phase epitaxy.
The researchers also employed an approach known as Glaser-Hay coupling (a reaction involving the coupling of cyclic molecules with terminal alkynes to form bisalkyne molecules) to form triple bonds in the quadritopic linkers, which yielded linear, interwoven polymer chains in a 2D array. The polymer sheet reaction and formation occur between the two sacrificial MOF films.
Polymers, if they adopt a regular crystal-like structure can be measured by many means. To identify whether they had created such a material, the researchers identified the molecular planes and position of the atoms within the textile to confirm the presence of a 2D sheet, with the MOF backbone still intact. This was done by employing x-ray diffraction (XRD) and infrared reflection–absorption spectroscopy (IRRAS), using Bruker D8 Diffractometers and Bruker Vertex equipment, respectively. Atomic force microscopy (AFM), also deduced that the individual polymer strands that make up the textile to be of the order of 200 nm in length.
The 2D textile sheets are easily transferable and can even be dissociated again under certain conditions. The researchers found that the polymer chains (of 200 nm) were longer than was theoretically expected. However, this is a good sign. The extra length is thought to be attributed to polymer molecules at the ends of each chain, which are unreacted. If this is the case, there is a large potential for these 2D sheets to be further interlocked with other 2D sheets and or/polymer chains to create large 2D polymer networks, which could be used to create controllable, large-scale 2D textiles in the future.
Wang Z., Blaszczyk A., Fuhr O., Heissler S., Wӧll C., Mayor M., Molecular weaving via surface-templated epitaxy of crystalline coordination networks, Nature Communications, 2017, 8, 14442
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