Sunday, May 13, 2018

Water: "Alan Turing’s chemistry hypothesis turned into a desalination filter"

From Ars Technica:

A chemical reaction he suggested can now be done, and it makes a great membrane.
Alan Turing is rightly famed for his contributions to computer science. But one of his key concepts—an autonomous system that can generate complex behavior from a few simple rules—also has applications in unexpected places, like animal behavior. One area where Turing himself applied the concept is in chemistry, and he published a paper describing how a single chemical reaction could create complex patterns like stripes if certain conditions are met.

It took us decades to figure out how to actually implement Turing's ideas about chemistry, but we've managed to create a number of reactions that display the behaviors he described. And now, a team of Chinese researchers has figured out how to use them to make something practical: a highly efficient desalination membrane.

From hypothesis to chemistry
Many chemical reactions end up going to completion, with all the possible reactants doing their thing and producing a product that's distributed uniformly within the reaction chamber. But under the right conditions, some chemical reactions don't reach equilibrium. These reactions are what interested Turing, since they could generate complex patterns.

Turing's paper on the topic focused on a reaction that could be controlled by the addition of two chemicals: an activator that promotes it and an inhibitor that slows it down. If you simply mix the two into a reaction, the outcome will simply depend on the balance between these two chemicals. But as Turing showed, interesting things can happen if you diffuse them into a reaction from different locations. And if the two chemicals diffuse at different rates, you can get complex patterns or reaction products like spots or tiger stripes.

Turing's paper describing these reactions came out in 1952; it wasn't until the 1990s that someone actually figured out how to make this happen. Now, researchers may have discovered a way to put Turing's ideas to practical use.

The use they focused on was the production of membranes used in desalination. We already know how to arrange chemical reactions to make very thin membranes with lots of pores by putting reactants in separate solvents that don't mix. That way, the membrane only forms at the interface between the water-based solution and the organic-based solution. While these membranes are highly effective, they typically face a trade-off: if you make a membrane so that water passes through more easily, you tend to allow more salt to pass through as well....MORE