Adsorption isotherms of poly(o-methoxyaniline)

Adsorption isotherms have been obtained for poly(o-methoxyaniline) (POMA) deposited from aqueous solutions onto glass substrates using UV-visible spectroscopy. Since the peaks in the UV-vis spectra are shifted due to dedoping of POMA during the adsorption process, isosbestic points had to be determined for estimating the amount of polymer adsorbed per unit area. Experiments were carried out at various temperatures. For 25 degrees C, the data could be fitted with a Gu isotherm equation, which indicates that the formation of aggregates occurs for high concentrations. For concentrations below 0.25 g/l, the data could be fitted with a traditional Langmuir-type adsorption isotherm. A Langmuir isotherm also applies to data at the other temperatures employed, viz. 15 degrees C, 40 degrees C, 60 degrees C and 80 degrees C, far which the corresponding equilibrium adsorption constants were calculated. The enthalpy, entropy and free energy adsorption values were then estimated, which showed that POMA adsorption is mostly entropy controlled. (C) 1998 Published by Elsevier Science S.A. All rights reserved.