We report on the variation of the dissociation of a Langmuir monolayer of arachidic acid at the air/water interface as a function of the subphase pH and for several cations (Cd 2+ , Ca 2+ , Mg 2+ , and Na + ) with the help of the polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) method. The infrared spectra give access to the relative concentration of acid and salt molecules and allow us to determine the influence of the subphase 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 Mg 2+ , and even more so that of Ca 2+ and Cd 2+ , requires the introduction of some complexation constant to be understood.

Optically isotropic films of an amorphous copolymer containing azobenzene moieties (pDR1M-co-MMA) were irradiated by interfering two circularly contrarotating polarized laser beams and permanent holographic diffraction gratings were prepared. These involve the formation of both birefringence and surface relief gratings. Using the Raman confocal microspectrometry, we have recorded various resonance enhanced polarized Raman spectra from the surface profile in order to get new insight into the orientational and angular distributions of the chromophore species. Different theoretical equations of the Raman scattering intensities, including a treatment taking into account the effect of the high numerical aperture objective, were thus derived. Calculations and simulations of these equations allowed us to extract the second 〈P 2 〉 and fourth 〈P 4 〉 coefficients of the chomophore orientation function in various regions of the surface grating and to obtain the corresponding information entropy normalized distribution functions. From the various shapes of the distribution functions we discuss the photoinduced effects and suggest that mass-transport effects must be also effective. Finally, in agreement with the modulated relative Raman intensities and four distinct distribution functions observed along the surface grating, we conclude that the orientational orders are primarily generated by an angular dependent photoselection process, which acts as an initializing force in the establishment of the various molecular organized domains. Such molecular organizations could occur in the viscoelastic state of the polymer and be responsible for an amplification of the light induced anisotropic effects in some regions (at the bottoms) and for a significant perturbation of the orientations in other regions (at the tops of the surface profile). In agreement with previous studies about the mechanisms of grating formation, these results are consistent with a model involving the existence of large pressure gradients due to a viscoelastic flow of the polymer.

Dynamical experimental studies of the diffraction efficiency, birefringence, and surface relief modulation were carried out on functionalized azopolymer films of p(DR1M-co-MMA) with a 12% mole fraction of DR1M. The gratings were recorded using two linearly polarized pump beams (λ = 514.5 nm) either with a parallel configuration (p+p) or (s+(-s)) or with orthogonal polarizations (p+s). A general Jones matricial approach in conjuction with real-time polarization analyses of the first order diffracted beam (S+1) appears to be a quite sensitive method to extract relevant parameters such as birefringence (Δn) and surface relief modulation (2Δd). The phase matrices have been developed considering the pump polarization of the two interfering beams and taking into account the orientational “angular hole-burning” model under low pump irradiances. Numerical calculations allow us to extract the time variations of Δn and 2Δd and to compare the various efficiencies in grating formation. The obtained values for Δn are then compared with polarimetric measurements and the basic mechanisms or driving forces in the relief formation are also discussed in connection with recently proposed phenomenological models.