Surface tension and contact angle measurements of a hexadecyl imidazolium surfactant adsorbed on a clay surface

The surface tension of 1,2-dimethyl-3-N-hexadecyl imidazolium tetrafluoroborate (Im BF4) as a function of concentration has been measured. Between 10−5 and 4 × 10−4 mol/L, the surface tension decreases with increasing imidazolium concentration. Aggregate formation appears to occur at a concentration near 4 × 10−4 mol/L for temperatures between 50 and 75 °C. Small angle neutron scattering measurements show the aggregates to be micelles with an aggregation number ≈83. Advancing and receding contact angles of Im BF4 surfactant solutions wetting pre-equilibrated mica surfaces show surfactant adsorption occurring at 10−6 mol/L. At 7 × 10−5 mol/L, a maximum in the hydrophobicity of the surface is measured, with a contact angle of 84° ± 2°. The results show that the Im BF4 surfactant adsorbs onto the mica surface and produces a hydrophobic surface, similar to the behavior of cetyl trimethyl ammonium bromide (CTAB). However, a hydrophobic surface forms at lower concentrations for the Im BF4 surfactant than the CTAB surfactant.