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Alan Turing's Chemistry Hypothesis Turned Into a Desalination Filter (arstechnica.com)
An anonymous reader quotes a report from Ars Technica: 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.
To make this a true Turing-style system, the researchers dissolved a large molecule in water. This had the effect of making the water more viscous, which slowed the diffusion of the activator. In addition, the molecule was chosen so that the activator would stick to it, slowing things down even further. The end result was a system similar to the ones defined over a half-century ago. Imaging of the features show that rather than simply thickening the membrane, the membrane retained the same width in these areas; instead, it bulged out to form the structures. That's critical, as the amount of surface area exposed to a salt solution should influence how much water gets through the membrane. In fact, the researchers confirmed that more water was purified when the new membranes were used (the version with the stripes outperformed the dotted one). Unfortunately, the researchers don't compare this system to commercially available membranes. The report has been published in the journal Science.
To make this a true Turing-style system, the researchers dissolved a large molecule in water. This had the effect of making the water more viscous, which slowed the diffusion of the activator. In addition, the molecule was chosen so that the activator would stick to it, slowing things down even further. The end result was a system similar to the ones defined over a half-century ago. Imaging of the features show that rather than simply thickening the membrane, the membrane retained the same width in these areas; instead, it bulged out to form the structures. That's critical, as the amount of surface area exposed to a salt solution should influence how much water gets through the membrane. In fact, the researchers confirmed that more water was purified when the new membranes were used (the version with the stripes outperformed the dotted one). Unfortunately, the researchers don't compare this system to commercially available membranes. The report has been published in the journal Science.
Turing structures arise when imbalances in diffusion rates make a stable steady-state system sensitive to small heterogeneous perturbations. For example, Turing patterns occur in chemical reactions when a fast-moving inhibitor controls the motion of a slower-moving activator. Tan et al. grew polyamide membranes by using interfacial polymerization, where the reactions occur at the interface between oil and water layers. The addition of polyvinyl alcohol to the aqueous phase reduced the diffusion of the monomer. This process generates membranes with more bumps, voids, and islands, which prove to be better for water desalination.