REORIENTATION PROCESSES AND SURFACE PHASE-TRANSITIONS .2. A THERMODYNAMIC INTERPRETATION OF THE ELECTROCAPILLARY DATA OF METHYLPYRIDINES ADSORPTION ON A MERCURY-ELECTRODE
P. Nikitas et A. Pappalouisi, REORIENTATION PROCESSES AND SURFACE PHASE-TRANSITIONS .2. A THERMODYNAMIC INTERPRETATION OF THE ELECTROCAPILLARY DATA OF METHYLPYRIDINES ADSORPTION ON A MERCURY-ELECTRODE, Electrochimica acta, 38(11), 1993, pp. 1573-1584
The thermodynamic method proposed in J. electroanal. Chem. 309, 1 (199
1) for analysis of adsorption data of organic compounds at electrified
interfaces is extended to adsorption layers of two-state adsorbates.
It is shown that the information which can be gained in such systems i
s considerably low in comparison with adsorption layers of constant-or
iented adsorbates. Thus, the excess free energy of mixing and excess e
ntropy cannot be calculated and only under optimum circumstances the G
ibbs energies of adsorption and the particle-particle interaction para
meter can be estimated. The thermodynamic method is applied to the stu
dy of the adsorption properties of 2- 3- and 4-methylpyridines on a me
rcury electrode from aqueous solutions of 0.1 N Na2SO4. It is shown th
at methylpyridines reorientate on the electrode surface from the flat
state to the normal one with the N atom facing the solution. At potent
ials more negative than -0.7 V (sce) the reorientation of 2- and 3-met
hylpyridines is accompanied with a phase separation process. The Gibbs
energies of adsorption and the particle-particle interaction paramete
r are estimated by means of the thermodynamic method and a correlation
with interfacial interactions is attempted. Finally, the values of th
e interaction parameter are compared with theoretical calculations and
discussed.