Designing the structure and relevant properties of semiclathrate hydrates by partly asymmetric alkylammonium salts

Abstract

Semiclathrate hydrates are host-guest materials that form from ionic guests and water. There are numerous options for the ionic guests, such as quaternary ammonium salts, to obtain functional properties of...

Discovery of the final primitive Frank-Kasper phase of clathrate hydrates

“…The relationship between molecular structures of quaternary ammonium cations and the combined cages which can be stabilized by the cations is shown in Fig. 4, e.g., well symmetric ions such as TBA (or N4444) ( 35 ) and tetra- i -pentylammonium (Ni5i5i5i5) ( 16 ) and partly asymmetric tri- n -butyl, n -pentylammonium (N4445) ( 41 ) cations, where, in abbreviation, N, 4, 5, and i5 denote nitrogen, n -butyl, n -pentyl, and i -pentyl, respectively. The n -hexyl chain is the only guest moiety that can stabilize the true form of the P cage with the 6true¯ m 2 symmetry required for the HS-I structure, which has never been stabilized by the other guests.…”

Guest size effects on a robust structure of semiclathrate hydrates and their thermophysical properties

“…Synthesis and characterization of the N3444 and N4445 cations were carried out by the same process in our previous study. 61 The resulting bromide salts were converted to chloride salts by ion exchange resin (IRA402BL CL Organo Co. Ltd, Tokyo, Japan), and the obtained solution was neutralized by hydrogen chloride solution (0.2 mol L −1 , FUJIFILM Wako Pure Chemical, Co.). It was confirmed that byproducts of tri- n -butylamine and bromide ion remaining in the converted salts were less than 0.1 mass percent using 1 H NMR and an ion chromatograph device (ICS-2000, Dionex Co.).…”

“…Further description of the melting temperature measurement method can be found elsewhere. [53][54][55][56]61…”

“…Ice and metastable hydrate phases were eliminated before measurements by an annealing process. [53][54][55][56]61,65 The heating rate was less than 1 K min À1 . The detailed procedures can be found elsewhere.…”

“…The detailed procedures can be found elsewhere. [53][54][55][56]61 The fusion heat was calibrated with that of cyclo-hexane (499.8%, FUJIFILM Wako Pure Chemical, Co.) reported in the literature. 66 The measurement uncertainty for specific enthalpy of fusion was 1 kJ kg À1 with 95% reliability.…”