THE SURFACE THERMODYNAMIC PROPERTIES OF TALC TREATED WITH OCTADECYLAMINE

The surface of talc is nearly apolar (γLW = 31.5, γ⊘ 2.4, and γ⊘ = 2.7 mJ/m2). The surface properties of talc can be modified by progressive coverage of the surface with an organic material. The present experiments used varying quantities (0-3% by weight) of (primarily) octadecylamine deposited on a talc powder. The surface properties were determined by thin layer wicking; the deposition of the octadecylamine resulted in the rapid loss of the Lewis acid (γ⊘) and base (γ⊘) character producing a completely apolar material. For the amine-treated samples, hydrocarbon liquids of varying surface tension (γL = 18.4 to 27.47 mJ/m2) continued to interact with the silicate surface (γLW = 28.5 mJ/m2) and spread, while the nonhydrocarbon liquids interacted with a lower energy surface, presumably the hydrocarbon tails of the octadecylamine, giving γLWS values as low as 15.7 mJ/m2. These observations are consistent with a surface having the octadecylamine chains oriented with the nitrogen toward the surface and with the alkyl chain perpendicular, or nearly so, to the talc surface. © 1993 by Academic Press, Inc.