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－35℃の過冷却状態までの水の構造
横山, 晴彦;梶原, みよ子;菅野, 等
Permalink : http://hdl.handle.net/2115/52339
Abstract
純水のＸ線回折測定により得られた－15℃の過冷却状態までの動径分布関数の～10.8Åの距離に特異的なピークが見出された. －15℃の過冷却水の動径分布関数は, 正12面体とその会合構造を含むガスハイドレートの水素結合ネットワークで表されるクラスレート様構造を仮定して説明することができた. このネットワークは正五角形５員環水素結合構造を基本単位にもち, かなり高い温度からその形成が始まる. 氷Ｉ様の水素結合構造は－15℃までの水中にはほとんど見られないが, エマルション粒子中で－35℃付近まで過冷却されたとき, この構造をもつクラスターも生成されることが分かった. 重水に対する測定からも同様の結果が得られた.
X-ray diffraction measurements have been carried out for pure liquid water at various temperatures down to －15℃ in the supercooled state. In the radial distribution functions (RDF) a specific peak was found at ～10.8Å and strengthened in the supercooled state. The RDF at －15℃ could be well explained by theoretical RDFs based on structure models assuming hydrogen-bonded networks in gas-hydrate crystals with some free water molecules in polyhedron cages,such as Pauling’s model. The gas-hydrate-like structures have pentagon structures composed of five water molecules as the structural unit, constructing the dodecahedrons and their aggregates. The formations of these structures seem to start at rather high temperatures above～25℃. The existence of the ice I-like structure could not be confirmed at temperatures down to －15℃, but the clusters having this structure were found to be formed in the emulsion particles by supercooling from －15℃ to －35℃, together with the formation of gas-hydrate-like structures. The structure of heavy water (D2O) was also investigated and elucidated to be essentially similar to that of ordinary water (H2O)although the hydrogen bonds in D2O were developed slightly more than in H2O at the same temperature.
X-ray diffraction measurements have been carried out for pure liquid water at various temperatures down to －15℃ in the supercooled state. In the radial distribution functions (RDF) a specific peak was found at ～10.8Å and strengthened in the supercooled state. The RDF at －15℃ could be well explained by theoretical RDFs based on structure models assuming hydrogen-bonded networks in gas-hydrate crystals with some free water molecules in polyhedron cages,such as Pauling’s model. The gas-hydrate-like structures have pentagon structures composed of five water molecules as the structural unit, constructing the dodecahedrons and their aggregates. The formations of these structures seem to start at rather high temperatures above～25℃. The existence of the ice I-like structure could not be confirmed at temperatures down to －15℃, but the clusters having this structure were found to be formed in the emulsion particles by supercooling from －15℃ to －35℃, together with the formation of gas-hydrate-like structures. The structure of heavy water (D2O) was also investigated and elucidated to be essentially similar to that of ordinary water (H2O)although the hydrogen bonds in D2O were developed slightly more than in H2O at the same temperature.
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