Study of the Formation of Precursor Clusters in an Aqueous Solution of KH<sub>2</sub>PO<sub>4</sub> by Small-Angle X-ray Scattering and Molecular Dynamics
oleh: Andrey E. Sukhanov, Petr V. Konarev, Vladimir I. Timofeev, Ildar F. Garipov, Ekaterina S. Smirnova, Georgy S. Peters, Kseniia B. Ilina, Yury V. Pisarevsky, Olga A. Alekseeva, Mikhail V. Kovalchuk
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2023-11-01 |
Deskripsi
The structure of an aqueous solution of potassium dihydrogen phosphate (KH<sub>2</sub>PO<sub>4</sub>, KDP) was studied by small-angle X-ray scattering (SAXS) and molecular dynamics (MD). According to SAXS data, the octameric species (KH<sub>2</sub>PO<sub>4</sub>)<sub>8</sub> are formed in solution in addition to K<sup>+</sup>, (H<sub>2</sub>PO<sub>4</sub>)<sup>−</sup>, and KH<sub>2</sub>PO<sub>4</sub>, while the presence of other types of oligomers is not observed. When the temperature drops below the saturation temperature (~60 °C), the volume fraction of octamers increases sharply, reaching 50% at 4 °C. The results of MD calculations of the temporal stability relationships of dimers (KH<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>, tetramers (KH<sub>2</sub>PO<sub>4</sub>)<sub>4</sub>, and octamers (KH<sub>2</sub>PO<sub>4</sub>)<sub>8</sub> show that the dimers and tetramers disintegrate rapidly (50–100 ps), while the octamers remain stable. A comparative analysis of the bonds between the octamers and the KDP crystal lattice was carried out when the octamer was inserted during crystal growth in the directions [001] and [100]. The possible relationship of the obtained results with the changes in the anisotropy of growth rates (habitus) of KDP crystals at different degrees of supersaturation is discussed.