Apolar. Lifshitz-van der Waals (gamma(LW)) and polar, acid-base (Lewis
) (gamma(AB)) surface free energy components, of monosized, spherical
ZnS colloidal particles were experimentally determined using the thin-
layer wicking technique. The results were compared with those obtained
on a pure, commercial sample of zinc sulfide. The fact that the synth
etized sample showed a very high electron-donor (gamma(s)-) component
suggested that some species, related in principle to surface oxidation
of ZnS during the synthesis reaction, could be formed on the surface
of the particles. To check for this possibility, the surface free ener
gy components of pure and oxidized ZnS, and of zinc oxide and sulfate,
were determined by both the contact angle and thin-layer wicking meth
ods. The similarity between gamma(s) components obtained with both met
hods for pure ZnS lead to the conclusion that both techniques give rel
iable results. The high gamma(s)-value determined for synthetic ZnS pa
rticles cannot be explained simply by surface oxidation of the colloid
al particles, since partially oxidized ZnS, or even zinc oxide or sulf
ate, gave very similar gamma(s)-, always lower than that found for syn
thetic spherical ZnS. The fact that the Lifshitz-van der Waals (gamma(
s)LW) component of the surface free energy is somewhat higher for the
latter material is believed to be related to elemental sulfur present
on the surface of the particles. The general compatibility of the resu
lts obtained by both methods suggests that the thin-layer wicking tech
nique is useful to further characterize these or other systems. partic
ularly if the examined material is sufficiently monodisperse.