A novel method for determining surface free energy of powders using Washburn's equation without calculating capillary factor and contact angle

Abstract

Measuring surface free energy (γs) of powders is important. When liquids are used as test probes, two primary techniques based on Washburn's equation can be used, namely, thin layer and column wetting methods. In the two methods, contact angles of n-alkane are assumed to be zero to obtain geometric or capillary factor. However, several researchers believe this assumption is irrational. In this paper, to avoid calculating geometric or capillary factor, an approach for determining γds of powders using Washburn's equation was established and confirmed by measurements for nanosized SiO2, ZnO, and TiO2 powders. When a series of n-alkanes was used, a linear relationship was found between square root of alkanes' γl and measured wetting result of w2tηρ2. This rule was deduced from Washburn's and Fowkes's equations and was supported by the wetting results. It was also found that after obtaining the equation of n-alkanes' line, γds of powders could be calculated from the slope and intercept of the line or from γl of an imaginary alkane. Due to the obtained γds of the powders from the developed method and IGC measurements were almost equal, it was believed that the developed method could be used in determining γds of powders.