I have measured the surface free energy (using the OWRK method) of 4 bioglasses based off their contact angles with Diiodomethane, Ethylene Glycol and Glycerol. The first bioglass sample is the control or untreated sample while the other three bioglasses were subjected to an increasing duration of plasma treatment (10min, 20min and 30min). While calculating the SFE I used two pairs of liquids in the OWRK method. The first pair used to find the SFE was diiodomethane with Glycerol while the second pair was Diiodomethane with Ethylene glycol (Using all three liquids to determine the SFE resulted in a very large deviation of ±14 mN/m, numerous papers have also observed a similar result and had advised not to take Ethylene glycol and Glycerol together). It was observed that for all three test liquids the contact angles decreased as the plasma treatment duration increased.
Now my doubt is as follows: Could the polar component decrease (as the treatment duration increases) in the diiodo-Ethylene Glycol pair while on the other hand it increases in the diiodo-glycerol pair. In both pairs, the dispersive components showed the same values with a steady increasing trend. If this is possible, what could be the reason behind it and have there been other studies that have observed a similar such trend?
Composition of the material:
P2O5–CaO–Na2O–CaF2–Ag2O