Solid surface energy precursor liquids

Where the parameter R is an averaged value of the apparent capillary radius of the thin porous layer (29). However, as shown in (33-35), Eq. [16] is valid only if a precursor duplex liquid (ilm is pre.sent ahead of the penetrating front of a liquid completely wetting the solid surface. Thus, from this equation it is clearly seen that the surface free energy of the substrate is not related to the rate of penetration of the liquid. Nevertheless, Eq. [16] is very useful for the determination of the R parameter of glass plates covered with the powder of the solid tested. Liquids most suitable for this purpose are the i-alkanes. like n-octane or n-decane. 

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