EFFECT OF POLY(OXYETHYLENE) CHAIN-LENGTH ON ELECTROSORPTION OF HEXA AND OCTA(ETHYLENE GLYCOL) MONO NORMAL-DODECYL ETHERS AT THE POLARIZED NITROBENZENE-WATER INTERFACE

The interfacial tension at the interface between a nitrobenzene solution of 0.1 mol dm-3 tetrapentyl-ammonium tetraphenylborate and an aqueous solution of 0.05 mol dm-3 lithium chloride has been measured as a function of the applied voltage across the interface at 25 °C in the presence of hexa- and octaethylene glycol monododecyl ethers, C12E6 and C12E8, in the nitrobenzene phase. Both C12E6 and C12E8 strongly adsorbed over the entire potential range of the polarized interface. The adsorption of C12E6 and C12E8 was stabilized by complex formation with Li+ ions in the aqueous phase, as is the case of C12E4 (T. Kakiuchi, T. Usui, and M. Senda, Bull. Chem. Soc. Jpn., 63, 2044 (1990).). The difference in the standard adsorption Gibbs energies between n=6 and 8, where n is the number of oxyethylene units, was twice as large as that between n=4 and 6, indicating that a chain length longer than 6 is preferable for the complex formation with Li+ ions at the interface. The surface activities of both C12E6 and C12E8 were markedly enhanced by a positive increase in the potential of the aqueous phase with respect to the potential in the nitrobenzene phase. This dependence of adsorption on the electrical potential difference indicates that the adsorbed C12E6 and C12E8 molecules behave as cationic surfactants, owing to the complex formation at the interface. © 1990 The Chemical Socity of Japan.