Phase transitions of adsorbed carboxylic acids on zinc oxide and of zinc soaps. Infrared and X-ray diffraction investigations

Summary The reaction between carboxylic acids in benzene solution and suspended zinc oxide particles was investigated by means of infrared spectrometry. The results show how the carboxyl groups react with the zinc oxide forming zinc carboxylate groups at the chemisorption. The chemisorbed acid forms a multilayer at the surface, which gives a new explanation of the protective action of adsorbed acids against flocculation of the particles in nonpolar solvents. The temperature-dependence of the spectra showed transitions at the same temperatures and of the same kind as the corresponding zinc carboxylates, whose spectra were also recorded. The zinc soaps exhibited thermotropic behaviour, and lyotrophy is suggested as the explanation of the multilayer formation.

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Zusammenfassung Mit Hilfe der Infrarotspektrometrie wurde die Einwirkung von Stearins?ure und ?ls?ure auf Zinkoxid untersucht, das in Benzol suspendiert worden war. Durch Carboxylatbildung wird eine multimolekulare Schicht der S?uren auf der Oberfl?che der Zinkpartikel ausgebildet. Die Partikel werden dadurch von der Flokkulation in nichtpolaren L?sungsmitteln geschützt. Die Temperaturabh?ngigkeit der Spektren entspricht der der Zinkcarboxylate.