WETTABILITY AND THE EVAPORATION RATES OF FLUIDS FROM SOLID-SURFACES

The interfacial forces which determine the interaction between a fluid and a solid surface have been investigated under dynamic conditions. The evaporation characteristics of fluid drops placed on solid surfaces have also been investigated. The rate of evaporation of drops of liquids placed on smooth solid surfaces with wetting characteristics, i.e. contact angle, THETA, < 90-degrees (water on glass), was found to be different from that in the case of non-wetting liquids, i.e. THETA > 90-degrees (water/Teflon). If THETA is less than 90-degrees, the evaporation rates are linear; however, if THETA > 90-degrees, the rates are non-linear. In the case of THETA < 90-degrees, THETA decreases and the radius of the contact area between the liquid and solid stays constant. However, in the case where THETA > 90-degrees, the contact angle remains constant and the interfacial line of contact decreases under evaporation. The evaporation rates of fluids from porous solids provide useful information about porosity and the characteristics of the pore size, and the data allow one to measure the pore volume. These data were found to agree with the pore volume data obtained by other methods (such as Hg porosimetry and BET).