SURFACE AND THERMODYNAMIC PARAMETERS OF SOME CATIONIC SURFACTANTS

Three cationic surfactants were prepared by condensing 1-chlorododecan e 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(hydr oxyethyl)ammonium chloride. The surface and thermodynamic properties o f 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 notation process. The properties studi ed included surface excess concentration (Gamma(max)), critical micell e concentration (cmc), free energy of micellization (Delta G(mic)(o)), and adsorption (Delta G(ads)(o)) in addition to the surface tension ( gamma(cmc)) at the cmc, effectiveness (Pi(cmc)), anti efficiency (C-p( 20)) of a surfactant to reduce the surface tension of water. The effec t of temperature on surface and thermodynamic properties was investiga ted by making measurements at 25, 35, 45, and 55 degrees C. The result s showed that the number of the hydrophilic portions of the prepared c ationic surfactants plays a major role in determining their thermodyna mic properties. The values of Gamma(max), Delta G(mic)(o), and Delta G (ads)(o) were found to increase with increasing number of ethanol grou ps substituted on the nitrogen atom, fi om one to three, while cmc and surface area occupied by one molecule (A(max)) were decreased. The re sults suggest that the surfactant N-dodecyl-N,N,N-tris(hydroxyethyl)am monium chloride may be preferable as a notation collector to the other surfactants having a lower number of ethanol groups.