Neutron scattering study of polyamorphic THF·17(H2O) – toward a generalized picture of amorphous states and structures derived from clathrate hydrates
| Autor: | Paulo H. B. Brant Carvalho, Mikhail Ivanov, Ove Andersson, Thomas Loerting, Marion Bauer, Chris A. Tulk, Bianca Haberl, Luke L. Daemen, Jamie J. Molaison, Katrin Amann-Winkel, Alexander P. Lyubartsev, Craig L. Bull, Nicholas P. Funnell, Ulrich Häussermann |
|---|---|
| Rok vydání: | 2023 |
| Předmět: | |
| Zdroj: | Physical Chemistry Chemical Physics |
| ISSN: | 1463-9084 1463-9076 |
| DOI: | 10.1039/d3cp00539a |
| Popis: | From crystalline tetrahydrofuran clathrate hydrate, THF-CH (THF·17H2O, cubic structure II), three distinct polyamorphs can be derived. First, THF-CH undergoes pressure-induced amorphization when pressurized to 1.3 GPa in the temperature range 77-140 K to a form which, in analogy to pure ice, may be called high-density amorphous (HDA). Second, HDA can be converted to a densified form, VHDA, upon heat-cycling at 1.8 GPa to 180 K. Decompression of VHDA to atmospheric pressure below 130 K produces the third form, recovered amorphous (RA). Results from neutron scattering experiments and molecular dynamics simulations provide a generalized picture of the structure of amorphous THF hydrates with respect to crystalline THF-CH and liquid THF·17H2O solution (∼2.5 M). Although fully amorphous, HDA is heterogeneous with two length scales for water-water correlations (less dense local water structure) and guest-water correlations (denser THF hydration structure). The hydration structure of THF is influenced by guest-host hydrogen bonding. THF molecules maintain a quasiregular array, reminiscent of the crystalline state, and their hydration structure (out to 5 Å) constitutes ∼23H2O. The local water structure in HDA is reminiscent of pure HDA-ice featuring 5-coordinated H2O. In VHDA, the hydration structure of HDA is maintained but the local water structure is densified and resembles pure VHDA-ice with 6-coordinated H2O. The hydration structure of THF in RA constitutes ∼18 H2O molecules and the water structure corresponds to a strictly 4-coordinated network, as in the liquid. Both VHDA and RA can be considered as homogeneous. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|