Surface and Thermodynamic Parameters of Some Cationic Surfactants

Three cationic surfactants were prepared by condensing 1-chlorododecane with stoichiometric amounts of either mono-, di-, or triethanolamine. They are: N -dodecyl- N -mono(hydroxyethyl)ammonium chloride, N -dodecyl- N, N -bis(hydroxyethyl)ammonium chloride, and N -dodecyl- N, N, N -tris(hydroxyethyl)ammonium chloride. The surface and thermodynamic properties of these surfactants were investigated to find the relationship between the structure of the hydrophilic portion of such compounds and their efficiency as collectors in the flotation process. The properties studied included surface excess concentration (Γ max ), critical micelle concentration (cmc), free energy of micellization (Δ G ° mic ), and adsorption (Δ G ° ads ) in addition to the surface tension (γ cmc ) at the cmc, effectiveness (Π cmc ), and efficiency ( p C 20 ) of a surfactant to reduce the surface tension of water. The effect of temperature on surface and thermodynamic properties was investigated by making measurements at 25, 35, 45, and 55 °C. The results showed that the number of the hydrophilic portions of the prepared cationic surfactants plays a major role in determining their thermodynamic properties. The values of Γ max, Δ G ° mic, and Δ G ° ads were found to increase with increasing number of ethanol groups substituted on the nitrogen atom, from one to three, while cmc and surface area occupied by one molecule ( A max ) were decreased. The results suggest that the surfactant N -dodecyl- N, N, N -tris(hydroxyethyl)ammonium chloride may be preferable as a flotation collector to the other surfactants having a lower number of ethanol groups.