2009 Volume 50 Issue 3 Pages 695-701
The chemisorption isotherm of stearic acid on a calcite powder was established by calculating the amounts adsorbed using a UV-Visible spectrophotometer. The changes in surface properties of the calcite powder with the surface treatment were examined using contact angle measurements and inverse gas chromatography (IGC) at an infinite dilution. The adsorption of stearic acid was available only at their dilute concentration. The contact angle with water and formamide increased with increasing amount of stearic acid adsorbed on the calcite powder. The adsorption of stearic acid onto the calcite powder surface resulted in a significant decrease in the dispersive component of the surface free energy, γSD of calcite powder. The γSD value of calcite powder with 90% surface coverage was 27.2 mJ·m−2 at 120°C, whereas that of untreated calcite powder was 103.3 mJ·m−2. The standard adsorption enthalpy, −ΔHA0 values of the non-polar probes (n-alkanes) for stearic acid-treated calcite powder had decreased to almost the heat of liquefaction of the corresponding probes. The specific component of the surface free energy, −ΔGASP values of the polar probes for stearic acid-treated calcite powder were lower than those of untreated calcite powder.