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Adsorption studies were carried out from solutions of alkyl dithiocarbormtes (xanthates) or alkyl carboxylates and from mixtures of these anionic species with cationic alkyl trimethyl ammonium bromides (C n TAB). The substrates consisted of polished copper plates in three states of oxidation, i.e. either with a thick oxide coating left after polishing, a thin oxide residue left after acid etching, or an adsorbed layer of oxygen formed on vacuum deposition of copper film.The infrared reflectance spectra of the copper plates have indicated that the nature of the adsorbed species is not limited to a single constituent. In adsorption of lauric acid, either cupric laurate, laurate ion, or a mixture of the two species can be detected in the spectra of the adsorbed coatings. The degree of hydroxylation of copper surface and the degree of ionization of the adsorbate appear to be governed by the pH at the copper/liquid interface and not by the pH in the bulk of solution; in turn, the interfacial pH is determined by the amount of copper oxide present initially at the solid surface and undergoing dissolution during treatment with the solution of adsorbate.Adsorption from mixtures of sodium laurate and C n TAB was found to depend on the relative chain lengths; C 12 TAB yielded a precipitate containing laurate ion and lauric acid, together with C 12 TA ion, and resulted in slowing the adsorption (as cupric laurate); on the other hand, C 18 TAB kept laurate ions in mixed micelles which completely prevented adsorption of either component on copper substrates.In solutions of alkyl xanthates, cuprous xanthate was the main product of adsorption, with dixanthogen coadsorbing mainly when short chain xanthates (i.e. ethyl) were used. With mixed solutions, no coadsorption of C n TAB was detected, but the rate of xanthate adsorption was increased severalfold; in addition, complexed xanthate−C n TAB species were capable of adsorbing under conditions when uncomplexed xanthate ion did not adsorb (i.e. when free oxygen and oxide layers were excluded from the system).

Spectrophotometric studies on surfactants. II. Infrared study of adsorption from solutions of single and mixed surfactants, on copper substrates