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General Introduction
paramagnetic species (Hamza et al., 1981 and Serratrice et al., 1985). The results were
rationalized on the basis of the easiness of formation of cavities within the liquid rather
than the existence of any specific interaction again indicating that the cavities opened by
these solutes in perfluoroalkanes are significantly larger than in alkanes. Oxygen solubility
depends somewhat on molecular structure. For similar molecular weight, the differences in
O2 solubility can reach 20-25%. Linear perfluoroalkanes, including those that have a
double bond, an oxygen atom, or a terminal bromine atom, have an advantage over the
cyclic and polycyclic perfluoroalkanes (Riess, 1984). Terminal alkyl chain resulted in
slightly reduced O2 solubility (Meinert and Knoblish, 1993).
When perfluoroalkanes are mixed with alkanes, the deviations from ideality are
positive and larger than those of nearly all other classes of mixtures containing only nonpolar
and non-eletrolyte substances. The most striking consequences of the extent of the
deviations are, in bulk properties, marked positive azeotopy (double azeotrope can even
arise in the perfluorobenzene/benzeme system) and usually liquid-liquid immiscibility
(Scott, 1958) and also in surface properties, negative aneotropy or surface azeotropy
(McLure et al., 1973). Differences in chain flexibility of the two component molecules and
the weak interaction energy interplay are most probably the main responsible for the
occurrence of these phenomena (Calado et al., 1978).
I.3. Applications
The first fluorinated compounds were synthesised during the II World War, as part
of the Manhattan project, when scientists were looking for a material that was able to resist
to chemical attack and long-term thermal stability at high temperatures to serve as coating
for volatile elements in radioactive isotope production. The importance of the inclusion of
fluorine atoms in organic molecules is well documented from the number of
publications/year regarding fluorinated compounds, which increased from ≈ 35 in 1960 to
≈ 910 in 2004. The first articles relating synthesis, purification and measurement of
physical properties of highly fluorinated perfluoroalkanes were published in the fifties.
Since then, a constant increase in the number of publications occurred till 1990. In the last
fifteen years, the number of publications/year increased from ≈ 70 (in 1990) to ≈ 200 (in
2004). The increase in the number of publications verified in the last years is related with
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