Effect of cations on the dissociation of arachidic acid monolayers on water studied by polarization-modulated infrared reflection-absorption spectroscopy
E. Le Calvez et al., Effect of cations on the dissociation of arachidic acid monolayers on water studied by polarization-modulated infrared reflection-absorption spectroscopy, LANGMUIR, 17(3), 2001, pp. 670-674
We report on the variation of the dissociation of a Langmuir monolayer of a
rachidic acid at the air/water interface as a function of the subphase pH a
nd for several cations (Cd2+, Ca2+, Mg2+, and Na+) with the help of the pol
arization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS)
method. The infrared spectra give access to the relative concentration of a
cid and salt molecules and allow us to determine the influence of the subph
ase pH on the acid dissociation reaction for each cation. It is shown that
Na+ obeys the purely electrostatic Gouy-Chapman theory quite well, whereas
the behavior of Mg2+, and even more so that of Ca2+ and Cd2+, requires the
introduction of some complexation constant to be understood.