It is difficult for me to remember a London Underground train journey that I have taken in recent years where I haven’t seen at least one person knitting or crocheting. Now scientists have found a way for molecules to get in on the yarn-craft movement by weaving long chain molecules together for the first time.
A group of scientists in California working in collaboration with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California Berkeley have for the first time managed to chemically coax long helical organic threads of a chemical called phenanthroline to twist around and past each other to create what is known as a covalent organic framework, or COF.
As these materials have a low density framework and a high degree of porosity and large surface area, they can be used in everything from separation chemistry to insulation, and from mopping up spillages to efficiently catalysing reactions. Due to their delicate framework however, they are also mechanically weak. By weaving this long chain molecule, scientists have managed to produce much stronger COFs that could be functionalised in a range of ways for any of these applications.
To do this, they used a copper (I) complex material as a template for weaving. This template brought the phenanthroline threads together in a specifically desired pattern to produce a mesh-like network made of this molecule that is snazzily called COF-505. While the copper is used as a template, the presence of the copper ions in what is technically now metal organic framework, or MOF, causes the meshed molecules be stiff. The ions can be easily removed however, giving rise to incredibly flexible properties of the material, with a ten fold increase in the material’s elasticity. Restoring the copper ions reintroduces stiffness in the material. The removal and replacement of copper ions does not degrade the material, nor does it change the microstructure in any reported way.
A diagram of the regular cross-linking between these woven molecules that gives rise to its... [+]
While other covalent organic frameworks have previously been created, the novelty here is the method of construction of the framework which, rather than being made of parallel threads alone instead has a woven pattern where the polymer chains cross at regular intervals, with each crossing point acting as a point of flexibility.
Professor Omar Yaghi, who works in both Berkeley Labs’ Materials Science Division and the UC Berkeley Chemistry Department, say that by weaving molecules together in this method, they may be able to demonstrate “significant advances in structural flexibility, resiliency, and reversibility over other COFs” without the structure collapsing, thanks to the woven pattern. Furthermore the same team have developed what they call ‘reticular chemistry’ whereby these frameworks are functionalised through the application of catalysts to serve a range of applications such as converting carbon dioxide to carbon monoxide for use in product manufacture.
Much like any other woven materials, these COFs have high porosity and therefore a high internal surface area, making it perfect for optimising a range of catalytic reactions, perhaps even solar energy conversion. So while my actual knitting skills may not be up to scratch, perhaps I’ll be better at nano-weaving. Thankfully no nano knitting needles are required in this crafty materials endeavour.
