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Langmuir, 1992
The critical micelle concentrations of mixed binary cationic surfactant systems have been determi... more The critical micelle concentrations of mixed binary cationic surfactant systems have been determined in water by conductivity measurements. The following systems have been studied trimethyltetradecylammonium chloride + benzyldimethyltetradecylammonium chloride (I); trimethyltetradecylammonium chloride + benzyldimethylhexadecylammonium chloride (11); hexadecylpyridinium chloride + benzyldimethylhexadecylammonium chloride (111); trimethyltetradecylammonium bromide + didodecyldimethylammonium bromide (IV). Some additional single surfactant solutions were also investigated. The concentration domain studied extended to 10-20 times the critical micelle concentration (cmc). It is shown that for surfactants with more than 16 methylene groups (including the contribution of the head-group hydrophobicity), two breaks in the conductivity versus concentration plots are clearly observed. The effects are larger with mixed micelles than with pure ones. The first break corresponds to the classical cmc (C1), with a close-to-ideal mixing behavior for systems 1-111. The second break, which is observed for the mixed surfactants at concentrations about 3 times the first one, should be considered as a second cmc (C2). It is shown that the degree of counterion binding is a characteristic constant of the surfactant system investigated only above Cz. These findings are interpreted by assuming structural micellar transitions for long chain surfactants without added salt. The specificity of system IV with respect to the three other binaries is also considered. For example with this surfactant pair, contrary to the micellization process, counterion binding in very dilute surfactant concentration seems to be favored by mixing the single and the double chain surfactant. The relation of these observations to the well-known lamellae structures induced by double-chain surfactants is discussed.
Http Www Theses Fr, 1993
Les proprietes physicochimiques de plusieurs types de melanges de composes tensioactifs cationiqu... more Les proprietes physicochimiques de plusieurs types de melanges de composes tensioactifs cationiques ont ete etudiees dans l'eau afin de mettre en evidence les relations entre la structure de micelles mixtes et les proprietes solubilisantes de ces milieux. La mesure de la concentration micellaire critique (cmc) et du degre condensation des contre-ions par une technique de conductivite associes a l'utilisation d'une theorie electrostatique de la condensation ionique a permis de montrer que le nombre d'agregation des micelles varie de maniere ideale avec la composition de la solution. Des mesures de diffraction neutronique aux petits angles ont confirme la prevision theorique. Une seconde cmc a ete observee pour les melanges etudies. Lorsque la chaine hydrocarbonee d'un des surfactifs du melange etait superieure a 16 atomes de carbone. Une technique d'ultra-filtration a permis de montrer que cette seconde cmc etait liee a un changement de structure micellaire se traduisant par une augmentation de taille de micelles sans que la composition micellaire en soit affectee. La solubilisation de composes hydrophobes modeles a ete etudiee par une technique de calorimetrie permettant la determination simultanee des trois fonctions thermodynamiques essentielles : energie libre, enthalpie et entropie de solubilisation. Selon les systemes etudies, des effets de synergie negatifs et positifs ont ete observes. Les premiers sont susceptibles d'etre interpretes a partir d'un modele des solutions regulieres ; les seconds sont atypiques et peuvent etre ramenes au comportement des premiers par addition d'un sel inorganique
Langmuir, 1992
The critical micelle concentrations of mixed binary cationic surfactant systems have been determi... more The critical micelle concentrations of mixed binary cationic surfactant systems have been determined in water by conductivity measurements. The following systems have been studied trimethyltetradecylammonium chloride + benzyldimethyltetradecylammonium chloride (I); trimethyltetradecylammonium chloride + benzyldimethylhexadecylammonium chloride (11); hexadecylpyridinium chloride + benzyldimethylhexadecylammonium chloride (111); trimethyltetradecylammonium bromide + didodecyldimethylammonium bromide (IV). Some additional single surfactant solutions were also investigated. The concentration domain studied extended to 10-20 times the critical micelle concentration (cmc). It is shown that for surfactants with more than 16 methylene groups (including the contribution of the head-group hydrophobicity), two breaks in the conductivity versus concentration plots are clearly observed. The effects are larger with mixed micelles than with pure ones. The first break corresponds to the classical cmc (C1), with a close-to-ideal mixing behavior for systems 1-111. The second break, which is observed for the mixed surfactants at concentrations about 3 times the first one, should be considered as a second cmc (C2). It is shown that the degree of counterion binding is a characteristic constant of the surfactant system investigated only above Cz. These findings are interpreted by assuming structural micellar transitions for long chain surfactants without added salt. The specificity of system IV with respect to the three other binaries is also considered. For example with this surfactant pair, contrary to the micellization process, counterion binding in very dilute surfactant concentration seems to be favored by mixing the single and the double chain surfactant. The relation of these observations to the well-known lamellae structures induced by double-chain surfactants is discussed.
Http Www Theses Fr, 1993
Les proprietes physicochimiques de plusieurs types de melanges de composes tensioactifs cationiqu... more Les proprietes physicochimiques de plusieurs types de melanges de composes tensioactifs cationiques ont ete etudiees dans l'eau afin de mettre en evidence les relations entre la structure de micelles mixtes et les proprietes solubilisantes de ces milieux. La mesure de la concentration micellaire critique (cmc) et du degre condensation des contre-ions par une technique de conductivite associes a l'utilisation d'une theorie electrostatique de la condensation ionique a permis de montrer que le nombre d'agregation des micelles varie de maniere ideale avec la composition de la solution. Des mesures de diffraction neutronique aux petits angles ont confirme la prevision theorique. Une seconde cmc a ete observee pour les melanges etudies. Lorsque la chaine hydrocarbonee d'un des surfactifs du melange etait superieure a 16 atomes de carbone. Une technique d'ultra-filtration a permis de montrer que cette seconde cmc etait liee a un changement de structure micellaire se traduisant par une augmentation de taille de micelles sans que la composition micellaire en soit affectee. La solubilisation de composes hydrophobes modeles a ete etudiee par une technique de calorimetrie permettant la determination simultanee des trois fonctions thermodynamiques essentielles : energie libre, enthalpie et entropie de solubilisation. Selon les systemes etudies, des effets de synergie negatifs et positifs ont ete observes. Les premiers sont susceptibles d'etre interpretes a partir d'un modele des solutions regulieres ; les seconds sont atypiques et peuvent etre ramenes au comportement des premiers par addition d'un sel inorganique