Surface free energy and wettability of silyl layers on silicon determined from contact angle hysteresis

Using the literature data [A.Y. Fadeev and T.J. McCarthy, Langmuir 15 (1999) 3759; A.Y. Fadeev and T.J. McCarthy, Langmuir 16 (2000) 7268] of the advancing and receding contact angles for water, diiodomethane and hexadecane measured on various hydrophobic silyl layers (mostly monolayers) produced on silicon wafers the apparent surface free energies γstot were calculated by applying new model of the contact angle hysteresis interpretation. It was found that, for the same silyl layer, the calculated γstot values to some degree depended on the probe liquid used. Therefore, thus calculated the surface free energies should be considered as apparent ones. Moreover, also the values of the dispersion component γsd of these layers depend on the probe liquid used, but to a less degree. This must be due to the strength of the force field originating from the probe liquid and the spacing between the interacting molecules. The relationships between γstot and γsd are discussed on the basis of the equations derived. It may be postulated that applying proposed model of the contact angle hysteresis and calculating the apparent total surface free energies and the dispersion contributions better insight into wetting properties of the silyled silicon surface can be achieved.