Influence of Dodecylamine Chloride on the Surface Free Energy of Kaolinite

Bronisław Jańczuk, Emil Chibowski, Tomasz Białopiotrowicz, Lucyna Hołysz and Anna Kliszcz
Department of Physical Chemistry, Institute of Chemistry Maria Curie-Skłodowska University, 20-031 Lublin, Poland

Abstract: Contact angles of glycerol and diiodomethane drops were measured on the surface of kaolin pellets covered with different amounts of dodecylamine chloride (DDACl) to as much as one monolayer. For a glycerol drop, the contact angle changed from 25.7° (bare surface) to 45.4° for the surface precoated with 0.125 monolayer of DDACl, but remained nearly constant above this level up to one monolayer. For a diiodomethane drop, the contact angle changed from 28.6° (bare surface) to 58.1° for one DDACl monolayer precoating. Using these contact angles and a modified Young equation, the dispersive and nondispersive components of the surface free energy of DDACl-covered kaolin were calculated. These data showed that in the extreme case (one monolayer) the dispersive component was reduced by the DDACl from ∼36 mJ/m2 (bare surface) to 25.4 mJ/m2, i.e., the value characteristic for paraffin (25.5 mJ/m2); however, the nondispersive component was not reduced to zero. A minimum value (15.83 mJ/m2) was determined for the sample covered with 0.125 DDACl monolayer (calculated), and a slight increase in the nondispersive component was observed for greater coverages. Such a change of the nondispersive component suggests that, at higher coverages, some adsorbed DDACl molecules were oriented with their polar ends off the surface. Based on the values of the γ sf d and γ sf n , the work of water spreading was calculated. This work was positive for the bare surface (32.8 mJ/m2) and methanol-treated (36.5 mJ/m2) kaolin surface, but negative for 0.125 DDACl monolayer precoating (-31.1 mJ/m2). It remained essentially unchanged for higher coverages. These data mean that bare and methanol-treated kaolinite surfaces were hydrophilic and that DDACl-treated surfaces were hydrophobic.

Key Words: Contact angle • Dodecylamine chloride • Hydrophobicity • Kaolinite • Surface free energy

Clays and Clay Minerals; February 1990 v. 38; no. 1; p. 53-56; DOI: 10.1346/CCMN.1990.0380107
© 1990, The Clay Minerals Society
Clay Minerals Society (www.clays.org)