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SUMMARY:Unveiling novel phase and properties of water through confinement 
 - Venkat Kapil\, University of Cambridge
DTSTART:20211004T153000Z
DTEND:20211004T160000Z
UID:TALK162313@talks.cam.ac.uk
CONTACT:Dr Christoph Schran
DESCRIPTION:Water in nano-confinement is ubiquitous in biology and geology
 \, and highly relevant for nanotechnology. Unfortunately\, the difficulty 
 in interpreting experiments and contrasting results from simulations using
  a plethora of models has prevented a consensus on the phase behavior of n
 anoconfined water. Here we predict the full pressure-temperature phase dia
 gram of monolayer water confined between graphene at first-principles accu
 racy by combining advances in state-of-the-art methods such as diffusion M
 onte Carlo\, density functional theory\, machine learning and advanced sta
 tistical sampling. We find that monolayer water exhibits surprisingly rich
  and diverse phase-behavior that is highly sensitive to the lateral pressu
 re applied by graphene sheets. At low pressures\, monolayer water exhibits
  rich polymorphsim with a non-monotonic dependence of the melting temperat
 ure with pressure. At typical experimental confinement pressures\, monolay
 er water can melt via a two-step mechanism\, through an intermediate ``hex
 atic like" phase\, in agreement with the KTHNY theory of phase transitions
  in 2D materials. The hexatic phase exhibits quasi-rotations of water mole
 cules similar to the free rotor phase of high-pressure hydrogen. High pres
 sures increase autoprotolysis events\, and eventually lead to a new superi
 onic phase at mild conditions compared to bulk. Our work comprehensively d
 escribes the phase behavior of monolayer confined water and outlines clear
  experimental routes for observing the hexatic and superionic phases. Furt
 hermore\, it suggests that confinement could be a route towards probing su
 perionic materials at mild conditions\, opening prospects for the developm
 ent of efficient battery materials.
LOCATION:Goldsmiths 1\, Lecture Theatre\, Department of Materials Science 
 & Metallurgy
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