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Abstract. The sensitivity of the pyranine fluorescence to protonation/deprotonation is used to follow modifications in cured sol-gel thin films. The acid concentration in the sol-gel solution is varied for TEOS-based coatings and a series of organically modified silanes Si(OR)3R' are added to the TEOS solution. The concentration of the organically modified silane is varied as well as the chain length of the alkylgroup (R').The stationary fluorescence measurements show that the equilibrium between the protonated and the deprotonated form of pyranine changes depending on the type of silica matrix. The deprotonated form is dominant in the cured SiO2 films and the protonation/deprotonation ratio of pyranine is constant for the different acid concentrations used. The protonated form becomes dominant as the concentration of Si(OR)3R' is increased and as the alkyl chain length (W) of the organically modified silanes is augmented.Emission anisotropy measurements of pyranine in the same coatings show that the rotational freedom of the molecule changes due to modifications in the cages for the TEOS-based coatings. These modifications are produced by the acid concentration used to prepare the coatings. An increase in the rotational freedom of pyranine is observed in the TEOS-Si(OR)3R' systems.

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Abstract:The interactions between poly(viny1 alcohol) and the surfactant sodium dodecyl sulphate in aqueous solutions have been investigated by means of static and dynamic fluorescence measurements. By static fluorescence measurements the onset of interaction, the critical aggregation concentration, is determined to be 6.5 mM at 20°C and 7.0 mM at 40°C. By dynamic fluorescence measurements without added quencher the influence on the lifetime of the fluorescent probe, pyrene, by the presence of the polymer is investigated. From measurements with an added quencher, dimethylbenzophenone, the surfactant aggregation numbers of the micellar aggregates formed upon interaction between the surfactant and the polymer and the quenching rate constant are obtained. At the two polymer concentrations, i.e., 0.2% and 2.0%, the surfactant aggregation numbers at low surfactant concentration are very small, but increase rapidly with increasing surfactant concentration. Comparisons are made with results from a system where poly(ethy1ene oxide) instead of poly(viny1 alcohol) is the polymer.Key words: dynamic fluorescence quenching, polymer-surfactant interactions, aggregation numbers. R6urn6: Faisant appel a des mesures de fluorescence statique et dynamique, on a examine les interactions entre l'alcool polyvinylique et l'agent tensioactif dodecylsulfate de sodium, en solutions aqueuses. Sur la base de mesures de fluorescence statique, on a determine qu'au dkbut des interactions, la concentration critique d'agrkgation est Cgale B 6,s mM B 20°C et 2 7,O mM i 40°C. Utilisant des mesures de fluorescence dynamique sans addition de dksactivant, on a CtudiC l'influence du polymkre sur le temps de vie de la sonde fluorescente, pyrkne. Sur la base de mesures effectuees en presence de dimtthylbenzophCnone agissant comme desactivant, on a pu determiner la constante de vitesse de dksactivation et les nombres d'agregation de l'agent tensioactif des agrkgats micellaires formCs lors de l'interaction entre l'agent tensioactif et le polymkre. Aux deux concentrations du polymkre, B savoir 0,2 et 2,0%, on realise que les nombres d'agrkgation de l'agent de surface sont trks faibles i la faible concentration de l'agent tensioactif, mais qu'ils augmentent rapidement avec une augmentation de la concentration de l'agent tensioactif. On fait des comparaisons avec les rksultats obtenus avec un systkme dans lequel le polymkre est du poly(oxyde d'tthylkne) au lieu de l'alcool polyvinylique.

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