Abstract
The solid-vapour surface tension has been determined by contact angle measurements with polar and non-polar liquids on flat solid surfaces using Axisymmetric Drop Shape Analysis (ADSA) and by capillary penetration experiments on rough and porous solids. For smooth and inert, well prepared solid surfaces (PTFE, FC 721 on mica, FEP, PET) the plot of γ lv cos Θ versus γ lv yields smooth curves which are consistent with the equation of state approach to calculate solid-vapour and solid-liquid interfacial tensions. Other experimental patterns of contact angle data are caused by surface roughness and non-inert solids which may result in contact angles incompatible to Young’s equation. An alternative way to obtain the solidvapour surface tension of rough and porous solids are capillary penetration experiments. The determination of the penetration velocity of liquids into rough and porous solids yields Kγ lv coΘ versus γ lv plots, which provide γ sv values for these systems; K is an unknown parameter of the constant geometry of the porous solid. The application of this concept was demonstrated for a hydrophobic PTFE powder and for hydrophilic Cellulose membranes.
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