ABSTRACT
In the case of powders, measuring surface energy properties is crucial in many in dustrial fields. Unfortunately, direct measurements of contact angles cannot be im plemented, as plane surfaces of several mm2 are not available. Thus much effort has been devoted in designing suitable experimental techniques to derive contact angles or surface energies of powders. In the crudest methods, a comparative hy-
drophobicity scale can be obtained by spontaneous immersion of powders in liq uids with controlled surface tensions [1-4] or by measuring oil-water partition co efficients [5]. If contact angle values are required, direct techniques on oriented films [5-9] or pressed pellets [10-11] or indirect techniques based on the analysis of liquid intrusion in porous media such as capillary rise [12-15] and pressure [1617] measurements or intrusion [18] and immersion [19] calorimetry can be imple mented. As discussed by Buckton [14], the determination of contact angles poses numerous theoretical problems especially for crystalline particles and the main conclusion of this author was that techniques based on vapor adsorption were more appropriate. Thus, it has been shown that direct determination of surface energies can be obtained by using inverse gas chromatography [20-23], immersion calo rimetry [24-26] or applying Gibbs formalism to gas adsorption isotherms [27-30].
