A vacuum microbalance technique for studies on the wettability of powders

A vacuum microbalance technique has been used to evaluate the wettability of powders. The rate of uptake, and equilibrium weight of uptake, of water vapour onto outgassed powder samples, of differing wettabilities, were determined at different known temperatures. Standard techniques of data analysis were used to establish the enthalpy, entropy and Gibb's free energy of the activation and adsorption processes. The values obtained appeared to be in the correct order of magnitude and those for activation clearly reflected the relative wettability of the powders. Tests for compensation demonstrated that with the exception of phenobarbitone, there was probably a common mechanism producing the adsorption.