2001 Volume 50 Issue 11 Pages 857-863
1H NMR spin-lattice relaxation time of ethylenediammonium dioctanoate (EDADO), a model dispersant (MD) for phthalocyanine blue (PhB) pigment, was examined with a high-resolution magic angle spinning (MAS) 1H NMR probe (1H Nano·nmrTM Probe). The adsorption mechanism of EDADO onto PhB was discussed on the basis of the spin-lattice relaxation time obtained by changing the polarity of the solvent and the temperature in the 1H NMR measurement. In addition to the deduction shown in our previous report that the adsorption of the MD molecule onto the pigment is induced by the coordination of a lone electron pair of a nitrogen atom of the amino group onto Cu(II) of PhB, it became clear that equilibrium among a diammonium salt, a half-salt, and diamine (ethylenediamine, EDA) is an important factor in the adsorption behavior. A comparison of measurements in chloroform-d and in methanol-d4 suggests that the complex of PhB and a half-salt composed of EDA and octanoic acid still has interaction with a carboxylic acid molecule through proton-transfer from the carboxylic acid to PhB (PhB of the complex and/or free PhB) and successive hydrogen bonding which may effect the dispersion of pigment in a nonpolar medium. The results obtained in this model system may afford a basis for explaining the good dispersing ability of poly(ammonium carboxylate), that is, polymeric dispersants in practical use.
