Purpose. The aim of this study was to relate the organization of several binary mixes with three physical parameters (surface energy, cohesion parameter, and particle size) of various materials blended with each other.

Methods. Four pharmaceutical compounds were selected for their surface energies and cohesion parameters. Binary mixes were prepared from different sieved fractions. The frequency and nature of the interactions between the particles were observed by scanning electron microscopy.

Results. As expected, interactions were determined by both the energetics and the relative particle size of the two compounds blended, the latter determining the mode of interaction. However, particle size was not the only factor influencing the organization of the blends as, sometimes, small particles of a material would not adhere to the coarser particles of the other. Thus, a surface energy derived parameter B/Aλ − A/Bλ appears to be a valuable estimating tool of the potentiality of interaction between the particles blended. No correlation between the cohesion parameters of the compounds and the organization of the resulting blends could be found.

Conclusions. Surface energy and particle size play a major role in the organization of a binary blend. However, they cannot explain separately the interactions observed between the fractions blended as reliable predictions require the use of both characteristics.