Dispersive Surface Energy

A set of IGC measurements with alkane probes gives their Vg values (specific retention volumes) which in turn are normalised values calculated from retention times. From these Vg values the free energy of absorption, ΔG can be calculated via:

ΔG = RT_mln(Vg)

where R is the universal gas constant, T_m is the measurement temperature (converted from °C to K).

From the slope of the curve of ΔG versus the number of carbon atoms N_c (the Dorris & Gray technique) it is possible to calculate the dispersion surface energy, γ_s^d from:

γ_s^d = 1/γ_CH2*[ΔG_CH2/2N.a_CH2]²

where N is Avogadro's number, γ_CH2 is the surface energy of a pure CH₂ surface, given by γ_CH2=35.6-0.058(Τ_m-20), a_CH2 is the area of a CH₂ group (6A²) and ΔG_CH2 is the (average) change in ΔG per CH₂ group.

Enter your Vg values and the ΔG values and γ_s^d are calculated for you. The data points and the least squares fit from which ΔG_CH2 is calculated are also shown.

Note: just for simulation purposes the unmodified retention times can be used instead of normalized Vg. The calculated γ_s^d will not be correct, but it can give a good impression of the behaviour of data.

Typical values of dispersive surface energies are:

The IGC apps are based on the inputs kindly provided by Dr Eric Brendlé of Adscientis who are specialists in IGC measurements.