Results and Discussion - New Synthetic Routes to Polyoxometalate Containing Ionic Liquids - page 49

character for a material in the same way as an optical spectrum is used for
spectrophotometric characterization of compounds.
Figure 24 Sketch of a rheometer for viscoelastic measurements. The viscoelastic sample is placed in a cup
and exposed to an external sinusoidal stress. This is plotted together with the strain response as a
function of time in order to determine the phase lag G (see green double arrow).
The rheological properties of ionic liquids in general are influenced by the degree of
electrostatic interaction between the ILs cation and anion. [67, 68] POM-ILs in particular
show a great change in their viscosity at room temperature because this temperature
region is close to their melting point. Furthermore the molecular volumes of ILs are
correlated with their viscosity and their electrical conductivity. [69] The viscosity of
inorganic ionic liquids like POM-ILs mainly depends on weak electrostatic interaction
forces. Dai and coworkers described a class of ionic liquids formed by titanium
tamplated polyoxometalates of the Keggin-type with sodium counterions. [69] These ionic
liquids show low viscosities ranging from 42 to 82 mPa·s. Their findings need however
to be treated critically as the investigated cluster as they describe them should not be
able to bind Lanthanides. Further, their IL requires 10 percent or more water present,
otherwise it is converted into a solid, which means that the liquid state at room