Читать книгу Open and Toroidal Electrophoresis - Tarso B. Ledur Kist - Страница 16

The introduction of ions into certain solvents makes some solvent molecules attach around these ions, producing one or more layers of solvent molecules. The number of layers mainly depends on the charge of the ions, while the number of water molecules per layer largely depends on the size of the ions. These layers are a result of the charge–permanent dipole interaction between the ions and the permanent dipoles of the solvent molecules. Since water is a small molecule with a large electric dipole moment, this interaction is very strong in water. Figure 1.2 illustrates the solvation of an anion in water and Figure 1.3 illustrates the solvation of a cation in water.

Table 1.1 Relative (static) permittivities of liquids at 20 C. Extracted from Wohlfart and Lechner (2008) [3].

Liquid
N-methylformamide	189.0
Formamide	111.0
N-ethylformamide	104.7a)
Water	80.100
Propylene carbonate	66.14
Methanoic acid (Formic acid)	51.1
Dimethyl sulfoxide	47.24
Glycerol	46.53
Ethylene glycol	41.4
N,N-dimethylacetamide	39.0
N,N-dimethylformamide	38.25
Acetonitrile	36.64
1,3-propanediol	35.1
Methanol	33.0
Ethanolamine	31.94
N,N-diethylformamide	29.6
2-pyrrolidone	28.18
Diethanolamine	25.75
Ethanol	25.3
Propan-2-one (Acetone)	21.01
1-propanol	20.8
2-propanol	20.18
Allyl alcohol	19.7
1-butanol	17.84
2-butanol	17.26
Cyclohexanone	16.1
Cyclopentanone	13.58
Trifluoroacetic acid	8.42
Tetrahydrofuran	7.6
Ethanoic acid (Acetic acid)	6.20
Propanoic acid	3.44
Dimethyl carbonate	3.087
1,4-dioxane	2.2189
Cyclohexane	2.0243
Hexane	1.8865

a) Calculated considering the change of 0.45% per C observed with the formamide derivatives at 20 C.

Figure 1.2 Schematic representation of chloride anion solvation in water.

Figure 1.3 Solvation of the sodium cation in water.