分子シミュレーションによる適度な超冷却による均質な氷核形成
1Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid , 28040 Madrid, Spain.
Journal of the American Chemical Society
|September 10, 2013
まとめ
この研究では,コンピュータシミュレーションを使用して,水中の均質な氷核化を調査しています. 結果は,溶解下の20K以上では,水の凍結が異質で均一でないことを示しています.
科学分野:
- 物理 物理学 物理学とは
- 化学 化学は化学です.
- 地質学 地質学 地質学
背景:
- 氷に凍る水の凍結は,複数の科学分野における重要な移行です.
- 均質な氷核の理解は,自然凍結現象の説明の鍵である.
研究 の 目的:
- コンピュータシミュレーションを通じて,水中の均質な氷の核形成を調査する.
- 臨界クラスターサイズと核形成率を,様々な零下温度下において決定する.
主な方法:
- シミュレーション用にTIP4P/2005とTIP4P/氷水モデルを使用しました.
- 自由エネルギーの障壁を分析するために,古典的核化理論 (CNT) を採用した.
- 核形成障壁の頂点にあるシミュレートされた重要なクラスター.
主要な成果:
- 臨界クラスターサイズは,温度が溶解点以下15Kから35Kまで下がるにつれて,約8000分子 (4nm) から約600分子 (1.7nm) に減少します.
- 氷と水の界面の自由エネルギーが計算され,実験データと一致して29(3) mN/mであった.
- シミュレートされた核化の速度は,実験的な測定値,特に低温で一致しています.
結論:
- 氷の均質な核形成の速度は,融化点以下の20K以上の温度で非常に遅くなる.
- この温度値を超えるすべての水の凍結は,異質な核形成によって起こらなければならないと予測する.
- この発見は,シミュレーション結果を,水の凍結行動に関する実験的観測と調和させています.
関連する概念動画
Phase Transitions: Melting and Freezing
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
Recrystallization: Solid–Solution Equilibria
Recrystallization is a purification technique used to separate impurities from solid compounds. In this technique, no chemical reactions occur. Instead, it exploits physical properties only, specifically, the solubility differences between the desired compound and impurities, either at a single temperature or at different temperatures, and under other selected conditions. The solid-solution equilibrium (solubility equilibrium) of each component in the solution represents a binary phase...
Phase Transitions: Vaporization and Condensation
The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize (convert into vapor). The process is called vaporization—a surface phenomenon. Vaporization occurs when the thermal motion of the molecules overcome the intermolecular forces, and the molecules (at the surface) escape into the gaseous state. When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules...
Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility
Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, and solubilities (miscibilities) of substances. Molar mass, molecular shape, and polarity affect the strength of different intermolecular forces, which influence the magnitude of physical properties across a family of molecules.
Temporary attractive forces like dispersion are present in all molecules, whether they are polar or nonpolar. They...
Temporary attractive forces like dispersion are present in all molecules, whether they are polar or nonpolar. They...
Molecular and Ionic Solids
Crystalline solids are divided into four types: molecular, ionic, metallic, and covalent network based on the type of constituent units and their interparticle interactions.
Molecular Solids
Molecular crystalline solids, such as ice, sucrose (table sugar), and iodine, are solids that are composed of neutral molecules as their constituent units. These molecules are held together by weak intermolecular forces such as London dispersion forces, dipole-dipole interactions, or hydrogen bonds, which...
Molecular Solids
Molecular crystalline solids, such as ice, sucrose (table sugar), and iodine, are solids that are composed of neutral molecules as their constituent units. These molecules are held together by weak intermolecular forces such as London dispersion forces, dipole-dipole interactions, or hydrogen bonds, which...
Phase Transitions: Sublimation and Deposition
Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and standard pressure, a piece of dry ice (solid CO2) sublimes, appearing to gradually disappear without ever forming any liquid. Snow and ice sublimate at temperatures below the melting point of water, a slow process that may be accelerated by winds and the reduced atmospheric pressures at high altitudes. When solid iodine is warmed, the solid sublimes...


