Fillers finite” dilution

This justifies the use of inverse gas chromatography (IGC) for filler surface energy characterization. This technique can be used in two very different modes infinite or finite dilution. 

Finally, it should be mentioned that a procedure similar to IGC, a finite dilution, can be applied to nitrogen adsorption isotherm and allow surface nanoroughness characterization of any filler (Lapra et al., 2004). 

In FMC the probe is at finite dilution and it is likely, in the case of some filler/solvent combinations, that the most active sites will always be occupied by the solvent molecules, therefore these sites may never be probed during the FMC experiment. This will almost certainly be true in cases where the solvent and filler have strong hydrogen bonding activity, i.e., alcohols with silica. However, it can be argued that in a polymer composite, particularly when additive or filler surface modifier adsorption from the matrix melt (or a liquid resin) is considered, the conditions of the FMC experiment are closer to reality. 

Inverse gas chromatographic measurements may be carried out both at infinite dilution and at finite solute concentrations [1]. In the first case vapours of testing solutes are injected onto the colurtm and their concentrations in the adsorbed layer proceed to zero. Testing substances interact with strong active sites on the examined surface. The retention data are then converted into, e.g. dispersive component of the surface free energy and specific component of free energy of adsorption. In the second case, i.e. at finite solute concentrations, the appropriate adsorption isotherms are used to describe the surface properties of polymer or filler. The differential isosteric heat of adsorption is also calculated under the assumption that the isotherms were obtained at small temperature intervals. 

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