Biomedical Engineering Reference
In-Depth Information
devices is connected with difficulties in the synthesis of the material,
especially for large-scale production. In recent years, new molten
salts that are in liquid state at room temperature, the so-called ionic
liquids, have played an important role in science and technology.
Their application in electrochemistry as electrolytes brought
successful and promising preparation methods for the future. Hence,
in this chapter, the focus is on the enhanced synthesis of organic
electroactive materials in ionic liquids.
3.2 STRUCTURE AND PROPERTIES OF IONIC LIQUIDS
In general, ionic liquids (ILs) are salts in molten state at room
temperature and usually consist of a bulky organic cation and
an inorganic anion. They have been known for almost 100 years
since the work of Walden on electrical conductivity study of
ethylammonium nitrate [1]. Another step in the development of
molten salts was investigations on chloroaluminate AlCl
-based
ILs [2, 3]. Applications of these ILs are, however, limited due to
their water sensitivity. Since the beginning of the 1990s, air- and
water-stable ILs have been synthesized. The recent years have
brought intense attention to the physical and chemical properties
of organic molten salts that are in liquid phase at room
temperature and are stable in the presence of moisture as
well [4-9]. The reason that these salts remain liquid at ambient
temperature is threefold. Seddon and coworkers mention low
symmetry of ions, which prevents packing of the lattice [10].
Other factors can be attributed to charge dissipation [7] and steric
hindrance effects [11] in ILs.
ILs can be divided in water-immiscible and -miscible compounds.
Hydrophobic ILs typically consist of anions such as PF
-
4
-
or Tf
N
-
and
6
2
the hydrophilic ILs of Cl
According to Anthony
et al., the water miscibility is affected strongly by the anion [12].
Also the cation has its impact on water affinity, since when the alkyl
chain is elongated, miscibility of the ionic liquid is decreased.
From an electrochemical point of view the promising
applications of ILs are in batteries [13, 14], capacitors [15-17],
-
, Br
-
, BF
-
or AlCl
-
4
4
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