水の分子モデルにおけるメタステーブルな液体-液体変換
Jeremy C Palmer1, Fausto Martelli2, Yang Liu3
1Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Nature
|June 20, 2014
まとめ
研究者らは,超冷却水における液体-液体相移行の決定的な証拠を提供している. この2つの液体状態の間の移行は結晶化ではなく,特定の条件下で起こり,異常な水の振る舞いを明らかにします.
科学分野:
- 物理化学 物理化学
- コンピューティング・マテリアル・サイエンス・サイエンス
- 熱力学は熱力学である.
背景:
- 液体の水は,凍結点を下回る冷却時に異常な熱力学的性質を示し,圧縮性と熱容量の増加を含む.
- 理論的なモデルでは,深冷水における液体-液体相移行 (LLPT) を提案しているが,実験的な検証は,氷の急速な結晶化によって妨げられている.
- 水モデルにおける観測された移行が真のLLPTまたは液晶移行を表すかどうかについては,議論がある.
研究 の 目的:
- 深度超冷却条件下でのST2水モデルにおける液体-液体移行の存在と性質を調査する.
- 水中のシミュレーションで,ファーストオーダーLLPTの賛成または反対の明確な証拠を提供するためです.
- 液体水相間の移行を制御する分子再配置と熱力学的基準を探求する.
主な方法:
- 6つの高度なサンプリング方法を使用して,ST2水モデルの自由エネルギー表面を計算しました.
- 移行中に調整シェルとトポロジカルリング構造の再編成を分析しました.
- 液体相と結晶相の間の熱力学的に逆行可能な経路をシミュレートした.
主要な成果:
- 同じ深冷超冷却の熱力学条件下で共存する2つの変安定液相と安定結晶相を特定した.
- 2つの液体相間の移行が第1次相移行の熱力学的基準を満たしていることを実証しました.
- 結晶化とは異なる2つの液体相の間の自由変動がST2モデルで観察された.
結論:
- 水のST2モデルにおける第1次流体から液体への移行の明確な証拠を提供した.
- この研究は,水モデルにおける移行の解釈に関する議論を解決し,真のLLPTを確認しました.
- 結晶化と液体リラクゼーションの間の時間スケールの分離が,LLPT.の観測を可能にする上で果たす重要な役割を強調する.
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