arXiv subjects

D. Homouz

Publications and source records attributed to D. Homouz.

3 recordsLinked to original sources

arXiv2020

The Peculiar Size and Temperature Dependence of Water Diffusion in Carbon Nanotubes studied with 2D NMR Diffusion-Relaxation D-T2eff Spectroscopy

It is well known that water inside hydrophobic nano-channels diffuses faster than bulk water. Recent theoretical studies have shown that this enhancement depends on the size of the hydrophobic nanochannels. However, experimental evidence of this dependence is lacking. Here, by combining two-dimensional Nuclear Magnetic Resonance (NMR) diffusion-relaxation D-T2eff spectroscopy in the stray field of a superconducting magnet, and Molecular Dynamics (MD) simulations, we analyze the size dependence of water dynamics inside carbon nanotubes (CNTs) of different diameters (1.1 nm to 6.0 nm), in the temperature range of 265K to 305K. Depending on the CNTs diameter, the nanotube water is shown to resolve in two or more tubular components acquiring different self-diffusion coefficients. Most notable, a favourable CNTs diameter range 3.0-4.5 nm is experimentally verified for the first time, in which water molecule dynamics at the centre of the CNTs exhibit distinctly non-Arrhenius behaviour, characterized by ultrafast diffusion and extraordinary fragility, a result of significant importance in the efforts to understand water behaviour in hydrophobic nanochannels.

physics.chem-ph↗

arXiv2007

Measurement of the 3-D Born-Oppenheimer Potential of a Proton in a Hydrogen Bonded System using Deep Inelastic Neutron Scattering: The Superprotonic Conductor Rb3H(SO4)2

Born-Oppenheimer (BO) potential in any material. The proton potential surfaces in the hydrogen bonded superprotonic conductor Rb3H(SO4)2 are extracted from the momentum distribution measured using Deep Inelastic Neutron Scattering(DINS). The potential has a single minimum along the bond direction, which accounts for the absence of the antiferroelectric transition seen in the deuterated material, and a saddle point off the bond direction for tunneling into the next well with a barrier height of 350 meV. The measured potential is in qualitative agreement with phenomenological double Morse potentials that have been used to describe hydrogen bonds in other systems.

cond-mat.other↗

arXiv2006

Water in Carbon Nanotubes Is Not the Same Old Stuff

The momentum distribution of the protons in ice Ih, ice VI, high density amorphous ice and water in carbon nanotubes at low temperatures has been measured using deep inelastic neutron scattering. We find that the momentum distribution for the water in the nanotubes is qualitatively unlike that in any other phase of water or ice. The kinetic energy of the protons is 35mev less than that in ice Ih at the same temperature, and the high momentum tail of the distribution, characteristic of the molecular covalent bond and the stretch mode of the proton in the hydrogen bonds, is not present. We observe a phase transition between 230K and 268K in the nanotube data. The high momentum tail is present in the higher temperature measurement, which resembles that of ice Ih at the same temperature. Molecular dynamics simulations show the phase transition to be associated with the reordering of the hydrogen bonds of the 2-D ice layer, coating the interior of the nanotube at low temperatures, into a 3-D structure at 268K. We conclude that the protons in the hydrogen bonds in the 2-D ice layer are coherently delocalized, and that the 2-D ice layer is a qualitatively new phase of ice.

cond-mat.mtrl-sci↗