イオンによる水の動態の加速と減速のメカニズム
Guillaume Stirnemann1, Erik Wernersson, Pavel Jungwirth
1Department of Chemistry, Ecole Normale Supérieure, UMR ENS-CNRS-UPMC 8640, 24 rue Lhomond, 75005 Paris, France.
Journal of the American Chemical Society
|July 20, 2013
まとめ
イオンは,遠距離ではなく,局所的に水のダイナミクスに影響します. 稀な溶液では,イオン効果は添加的であるが,濃縮された溶液では,水素化殻の重複と粘度の増加のために非線形減速を示している.
科学分野:
- 物理化学 物理化学
- 溶液化学について
- コンピューティング・ケミストリー
背景:
- 水中のイオンと溶液の相互作用に関する根本的な疑問が残っています.
- 水の構造と動態に対するイオンの局所的効果と長期的効果は,まだ議論されている.
- イオンと水の相互作用を理解することは,様々な化学的,生物学的プロセスにとって極めて重要です.
研究 の 目的:
- 水の方向転換と水素結合のダイナミクスに対するイオンの影響を調査する.
- 水溶液中のイオンの局所的効果と長期的効果を区別する.
- イオン-水力学に関する矛盾する実験的発見を調和させるため.
主な方法:
- 水性塩溶液の分子動力学シミュレーション.
- イオンと水の相互作用の分析モデリング.
- 水分子の方向転換と水素結合のダイナミクスの分析.
主要な成果:
- イオンは,個々の水分子の方向転換に短期的な影響を及ぼします.
- イオン効果は,稀な溶液の添加物であり,相互作用の強さに基づいてダイナミクスを加速または減速します.
- 濃縮溶液は,水素化殻の重複と粘度の増加により,イオン型とは無関係な効果として,水の動態の非線形減速を示します.
結論:
- 水力学に対するイオンの影響は,主に短期的なものです.
- 単純な添加物モデルは,稀な溶液を効果的に記述します.
- 濃縮塩溶液は,イオン特異的な協力効果ではなく,構造変化による水動態を普遍的に遅らせます.
関連する概念動画
03:13Intermolecular Forces
Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
01:23Theory of Strong Electrolytes
The interionic forces of the strong electrolytes depend on the solvent's dielectric constant, which is the ability of a solvent to store electrical energy, based on its polarizability. and the solution's concentration. In high-dielectric solvents and in dilute solutions, weak electrostatic forces keep ions apart. However, in low-dielectric solvents or concentrated solutions, stronger interionic forces may cause ions to pair up as ionic doublets despite being fully ionized. The theory of strong...
01:07Damped Oscillations
In the real world, oscillations seldom follow true simple harmonic motion. A system that continues its motion indefinitely without losing its amplitude is termed undamped. However, friction of some sort usually dampens the motion, so it fades away or needs more force to continue. For example, a guitar string stops oscillating a few seconds after being plucked. Similarly, one must continually push a swing to keep a child swinging on a playground.
Although friction and other non-conservative...
Although friction and other non-conservative...
02:54Ions as Acids and Bases
Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
02:42Aqueous Solutions and Heats of Hydration
Water and other polar molecules are attracted to ions. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
04:01Factors Affecting Solubility
Compared with pure water, the solubility of an ionic compound is less in aqueous solutions containing a common ion (one also produced by dissolution of the ionic compound). This is an example of a phenomenon known as the common ion effect, which is a consequence of the law of mass action that may be explained using Le Chȃtelier’s principle. Consider the dissolution of silver iodide: