<< Liquids are structurally disordered, so it’s not immediately obvious how they can support two distinct structures with different densities. But that does seem to be possible for liquids in which some degree of directional bonding, such as hydrogen bonds between adjacent water molecules, makes distinct local structures possible. Liquid–liquid transitions have been reported, for example, in silicon, gallium, phosphorus and silicates. But finding one in supercooled water has proved very challenging. There have been previous claimed observations of a liquid–liquid transition in aqueous solutions at ambient pressure, (..) where the solute, such as the sugar glycerol, sometimes used as a cryoprotectant, lowers the freezing point. But such claims have been disputed.(..) Other researchers have reported liquid-like behaviour as the two well-established high- and low-density forms of amorphous (glass-like) ice interconvert. (..) >>
<< In 2014 Yoshiharu Suzuki (..) working with veteran water researcher Osamu Mishima, reported possible signs of a liquid–liquid transition, ending in a critical point where the two liquid states become indistinguishable, in emulsified, supercooled solutions of glycerol. (..) They saw signs of two distinct disordered states with different densities at a temperature of 150K. But there was no direct evidence that both were liquids, rather than amorphous ice. >>
<< Suzuki has now explored the same approach using trehalose as the solute – a sugar produced as a natural cryoprotectant by some organisms, such as insects, that experience extreme cold, to prevent their blood from freezing. He pressurised dilute emulsified solutions to about 0.6GPa at a range of temperatures below 159K, and then decompressed them again. >>
<< Such hysteresis – whereby the density jumps at different pressures on compression and decompression – is normal for a first-order transition where a parameter such as density changes discontinuously. It reflects the fact that the transition has to start with the chance formation of a ‘nucleus’ of the new phase, which then grows. >>
<< Suzuki is not yet sure why trehalose stabilises water so well against crystallisation, compared with glycerol – but this might help explain why life uses it as an antifreeze. >>
Philip Ball. Direct evidence emerges for the existence of two forms of liquid water. Feb 1, 2022.
Also
keyword 'water' in FonT
keyword 'transition' | 'transitional' in FonT
keyword 'transition' | 'transizion*' in Notes (quasi-stochastic poetry)
keywords: gst, transition, liquid-liquid transition, water
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