SURFACE THERMODYNAMIC PROPERTIES OF CADMIUM-SULFIDE

Measurements of the contact angle for water, formamide and diiodometha ne on pellets of cadmium sulfide were made. Also, the thin-layer wicki ng technique was used with n-decane, water and formamide as the penetr ating liquids. The measurements were used to determine apolar, Lifshit z-van der Waals (gamma(LW)) and polar, acid-base (Lewis) (gamma(AB)) s urface free energy components of monosized, spherical CdS colloidal pa rticles. The results were compared with those obtained on a pure, comm ercial sample of cadmium sulfide. They both are monopolar materials, a lthough synthetic CdS has a slightly higher electron-donor character ( Lewis base) (gamma(s)- = 61.4 mJ/m2) than commercial cadmium sulfide ( gamma(s)- = 56.0 mJ/m2). The gamma(LW) component has a similar value f or both samples, in the range of 44-47 mJ/m2. DELTAG121(TOT), the free energy of interaction between particles in aqueous medium is for both synthetic and commercial CdS around 34.0 mJ/m2. In spite of the (smal l) attractive contribution due to the Lifshitz-van der Waals interacti on (DELTAG121(LW)), the large acid-base repulsion would ensure stabili ty of CdS dispersions. Surface characteristics of the synthesized cadm ium sulfide are similar to those of polydispersed commercial particles concerning their wetting properties. In consequence, the stability of dispersions of either kind of particles is expected to be the same. H owever, the use of perfectly spherical particles of this material is s till valuable for testing model theories concerning interactions betwe en particles in suspension.