L'etude de la cinetique de gelification des gels d'alginate et de chitosane en fonction d... more L'etude de la cinetique de gelification des gels d'alginate et de chitosane en fonction de la temperature a ete effectuee a l'aide de mesures rheologiques oscillatoires qui permettent de determiner lesmodules visqueux et elastique a plusieurs frequences au cours du temps. L'observation experimentale du comportement en loi de puissance de ces modules a permis de verifier le critere de Winter pour ces systemes, de determiner le temps de gelification et de caracteriser les structures a ce temps par l'exposant de relaxation relie a une dimension fractale.
Ce travail porte sur l'etude de la transition sol-gel par analyse rheologique de composes a b... more Ce travail porte sur l'etude de la transition sol-gel par analyse rheologique de composes a base d'oxyde de titane obtenus par hydrolyse de butoxyde de titane, modifie chimiquement par de l'acetylacetone afin d'en reduire la reactivite et d'en controler le temps de gelification (tg). Les parametres influant sur tg sont nombreux et certains comme la temperature ou le taux d'hydrolyse ont deja ete etudies [1]. Ce travail poursuit l'etude de ces parametres. En effet, le taux de complexation et la concentration sont egalement des facteurs importants. La diminution du taux de complexation et l'augmentation de la concentration menent a une diminution de tg. Les mesures rheologiques en oscillations, outre la mesure du tg par la methode de Winter, nous permettent d'obtenir des informations sur l'evolution du processus d'agregation conduisant a la formation du reseau.
Nous presentons des mesures de la viscosite de cisaillement de solutions micellaires composees de... more Nous presentons des mesures de la viscosite de cisaillement de solutions micellaires composees de deux surfactants (chlorure de cetylpyridinium et salicylate de sodium) en fonction de la concentration et de la temperature. Nous avons utilise le modele de Carreau et une loi de puissance pour decrire le comportement rheofluidifiant observe. Ce dernier se produit au dela d'un gradient de cisaillement critique qui augmente avec la temperature. De plus, la dependance thermique de la viscosite a faible gradient de cisaillement est en bon accord avec une loi d'Arrhenius.
-Le traitement des eaux, qu'il s'agisse de production d'eau potable où d'épuration d'eau usée d'o... more -Le traitement des eaux, qu'il s'agisse de production d'eau potable où d'épuration d'eau usée d'origine urbaine ou industrielle, conduit toujours à la formation de boues que l'on sépare et de l'eau traitée. Ces boues se présentent à la sortie de la station d'épuration comme un liquide à forte teneur en eau. La teneur élevée en substances polluantes interdit le plus souvent leur rejet dans le milieu naturel sans précaution. Pour évaluer l'aptitude de ces boues au traitement, déterminer quels traitements leur faire subir, estimer les risques de pollution et enfin connaître leurs possibilités de réutilisation (agricole, énergétique ou autre). Dans ce cadre qu'il est défini l'objet de cette étude. L'étude consiste à étudier l'effet de traitement thermique sur le comportement physico-chimique et rhéologique des boues activées des stations d'épuration. Le traitement thermique des boues activées montre que l'augmentation de la température provoque une augmentation du pH et une diminution de la demande chimique en oxygène (DCO), et du rapport entre matières volatiles en suspension et matière en suspension (MVS/MES). Concernant l'aspect rhéologique pour les boues étudiées, le seuil de contrainte diminue avec l'augmentation de la température dans le même temps la viscosité apparente des boues diminue suivant une loi de puissance avec l'augmentation de la température.
We propose a theoretical study of the nonlinear propagation of a Gaussian laser beam in a mixture... more We propose a theoretical study of the nonlinear propagation of a Gaussian laser beam in a mixture of two liquids. Retaining electrostriction (dipole radiation forces), thermal expansion, and thermodiffusion (Soret effect) as the major mechanisms in the perturbation of the ...
ABSTRACT We analyze in this paper, the static and dynamic properties of the laser beam self-focus... more ABSTRACT We analyze in this paper, the static and dynamic properties of the laser beam self-focussing induced by a thermodiffusive (or Soret) effect in particle suspensions. We show theoretically that the beam radius exhibits oscillations along the propagation axis at the steady state, or at a given point during the transit time. These characteristics result from the nonlocality of the nonlinear process. We discuss the experimental conditions for observing these oscillations. Similar behaviors can be predicted in nonlinearities induced by other non local effects.
... A deacetylation degree of 84% was measured according to Brugnerotto's method... more ... A deacetylation degree of 84% was measured according to Brugnerotto's method, using FTIR spectroscopy.(29) The average viscosimetric molecular weight (M v = 1.0 × 10 6 g/mol) was determined by capillary viscosimetric measurements using the experimental conditions of ...
Micelle formation was followed by micro-DSC and rheology for aqueous solutions of two copolymers ... more Micelle formation was followed by micro-DSC and rheology for aqueous solutions of two copolymers of PEO-PPO-PEO, the Pluronic F127 (from BASF) and the EG56 (from PolymerExpert), a branched copolymer built with three chains of F127 type. It is shown that micellization is endothermic and that, for both polymers, the enthalpy of formation/melting is proportional to total concentration. The rheology of the solutions was carefully analyzed, before gelation for F127, and it reveals firstly the progressive changes of solubility of the unimers (decease of relative solution viscosity), followed by micelle formation over a 10 • C range. In this range, the micelle concentration dependence on temperature was deduced from enthalpy measurements and the corresponding volume fractions were derived. Viscosity was interpreted within the framework of well-known theories for hard sphere suspensions (Krieger-Dougherty or Quemada) based on an analogy between micelles and nanosized hairy grain suspensions. The gel state is achieved due to formation of the colloidal crystal. For EG56, the rheology is quite different; as the aggregation increases with temperature, a progression is observed from Newtonian to visco-elastic liquid. The characteristic frequency, defined by the relation G = G , for EG56 varies with temperature and the corresponding times increase by two orders of magnitude according to an Arrhenius law. The frequency dependence of G and G at different temperatures can be superposed with a horizontal shift factor and a small amplitude adjustment. There is no elastic solid formation in this case. The "gelation" of these two copolymers is compared to the physical gelation of cold-set gels (gelatin).
ABSTRACT Extensive dielectric measurements in the frequency range 100 kHz–15 GHz have been perfor... more ABSTRACT Extensive dielectric measurements in the frequency range 100 kHz–15 GHz have been performed at 25 °C on two oil-continuous microemulsion systems composed of water, n-dodecane, 1-pentanol, sodium dodecylsulfate and water, toluene, 1-butanol, sodium dodecylsulfate. It was found that in the above mentioned systems, the micellar phases display broad dielectric relaxation spectra which imply different dielectric processes. Two processes, occurring in the low frequency region around 1 and 100 MHz seem to be of ionic origin. They can be attributed to Maxwell–Wagner effect for heterogenous systems and the counterion movement in the interfacial layer around the micelles. The relaxation observed in the high frequency range (1 GHz) could possibly be attributed to the presence of water and alcohol in the vicinity of the reverse micellar surface. The strength of the dielectric relaxation process in the very high frequency region of about 16 GHz is dependent on the water content and is possibly related to pure water outside the interfacial layer.
A strong hysteretic behaviour has been observed for the self-focusing of a c.w. laser beam focuse... more A strong hysteretic behaviour has been observed for the self-focusing of a c.w. laser beam focused in a four-component micellar phase near a sponge phase in the phase diagram. All data demonstrate that the laser wave induces a structural change from the micellar phase towards a phase of droplets the nature of which is discussed. The recorded limit cycles and “creep” of cycles allow an analogy with the magnetization of a ferromagnetic material to be developed.
The aim of the present work is first to synthesis a magnetic chitosan hydrogel (chitosan ferrogel... more The aim of the present work is first to synthesis a magnetic chitosan hydrogel (chitosan ferrogel) using the blending method and second to study it rheological behavior. Magnetic components ( maghemite particles γ-Fe2O3 ) were synthesized via a simple chemical co-precipitation route also called Massart's procedure. Before being dispersed in chitosan network, γ-Fe2O3 particles were covered with a cationic polyelectrolyte (Polydiallyldimethylammonium chloride; PDADMAC) and the exact quantity required to cover the entire surface of maghemite particles was determined by Electrophoretic mobility. The successful functionalization of maghemite particles was confirmed by zeta potential measurement. The prepared ferrogel was gelified using glyoxal as crosslinking agent. The effect of continuous magnetic field on rheological properties of the elaborated ferrogel was studied, under controlled temperature before and after the gelation process, using a rotating rheometer fitted with a new ma...
Regeneration of thixotropic gels resulting from aggregation of positively charged magnetic nanopa... more Regeneration of thixotropic gels resulting from aggregation of positively charged magnetic nanoparticles is here investigated by mechanical spectroscopy. The frequency independence of the ratio G /G (G and G being respectively the viscous and the elastic moduli) at the gel point seen as a liquidsolid transition allows the determination of the gelation time t g and of the power law exponent on the angular frequency for both moduli (G ∼ ω , G ∼ ω ). This behaviour is similar to the one observed for classical chemical and physical gels. It implies a broad relaxation time spectrum which is compatible with previous dynamic magneto-optical birefringence measurements. The value of t g decreases exponentially with an increase of the pH that controls the interactions between particles through their surface density of charges. In contrast, the relaxation exponent is found to be nearly insensitive to the pH. A fractal dimension of 2.07 ± 0.06 is deduced from the power law exponent at the gelat...
L'etude de la cinetique de gelification des gels d'alginate et de chitosane en fonction d... more L'etude de la cinetique de gelification des gels d'alginate et de chitosane en fonction de la temperature a ete effectuee a l'aide de mesures rheologiques oscillatoires qui permettent de determiner lesmodules visqueux et elastique a plusieurs frequences au cours du temps. L'observation experimentale du comportement en loi de puissance de ces modules a permis de verifier le critere de Winter pour ces systemes, de determiner le temps de gelification et de caracteriser les structures a ce temps par l'exposant de relaxation relie a une dimension fractale.
Ce travail porte sur l'etude de la transition sol-gel par analyse rheologique de composes a b... more Ce travail porte sur l'etude de la transition sol-gel par analyse rheologique de composes a base d'oxyde de titane obtenus par hydrolyse de butoxyde de titane, modifie chimiquement par de l'acetylacetone afin d'en reduire la reactivite et d'en controler le temps de gelification (tg). Les parametres influant sur tg sont nombreux et certains comme la temperature ou le taux d'hydrolyse ont deja ete etudies [1]. Ce travail poursuit l'etude de ces parametres. En effet, le taux de complexation et la concentration sont egalement des facteurs importants. La diminution du taux de complexation et l'augmentation de la concentration menent a une diminution de tg. Les mesures rheologiques en oscillations, outre la mesure du tg par la methode de Winter, nous permettent d'obtenir des informations sur l'evolution du processus d'agregation conduisant a la formation du reseau.
Nous presentons des mesures de la viscosite de cisaillement de solutions micellaires composees de... more Nous presentons des mesures de la viscosite de cisaillement de solutions micellaires composees de deux surfactants (chlorure de cetylpyridinium et salicylate de sodium) en fonction de la concentration et de la temperature. Nous avons utilise le modele de Carreau et une loi de puissance pour decrire le comportement rheofluidifiant observe. Ce dernier se produit au dela d'un gradient de cisaillement critique qui augmente avec la temperature. De plus, la dependance thermique de la viscosite a faible gradient de cisaillement est en bon accord avec une loi d'Arrhenius.
-Le traitement des eaux, qu'il s'agisse de production d'eau potable où d'épuration d'eau usée d'o... more -Le traitement des eaux, qu'il s'agisse de production d'eau potable où d'épuration d'eau usée d'origine urbaine ou industrielle, conduit toujours à la formation de boues que l'on sépare et de l'eau traitée. Ces boues se présentent à la sortie de la station d'épuration comme un liquide à forte teneur en eau. La teneur élevée en substances polluantes interdit le plus souvent leur rejet dans le milieu naturel sans précaution. Pour évaluer l'aptitude de ces boues au traitement, déterminer quels traitements leur faire subir, estimer les risques de pollution et enfin connaître leurs possibilités de réutilisation (agricole, énergétique ou autre). Dans ce cadre qu'il est défini l'objet de cette étude. L'étude consiste à étudier l'effet de traitement thermique sur le comportement physico-chimique et rhéologique des boues activées des stations d'épuration. Le traitement thermique des boues activées montre que l'augmentation de la température provoque une augmentation du pH et une diminution de la demande chimique en oxygène (DCO), et du rapport entre matières volatiles en suspension et matière en suspension (MVS/MES). Concernant l'aspect rhéologique pour les boues étudiées, le seuil de contrainte diminue avec l'augmentation de la température dans le même temps la viscosité apparente des boues diminue suivant une loi de puissance avec l'augmentation de la température.
We propose a theoretical study of the nonlinear propagation of a Gaussian laser beam in a mixture... more We propose a theoretical study of the nonlinear propagation of a Gaussian laser beam in a mixture of two liquids. Retaining electrostriction (dipole radiation forces), thermal expansion, and thermodiffusion (Soret effect) as the major mechanisms in the perturbation of the ...
ABSTRACT We analyze in this paper, the static and dynamic properties of the laser beam self-focus... more ABSTRACT We analyze in this paper, the static and dynamic properties of the laser beam self-focussing induced by a thermodiffusive (or Soret) effect in particle suspensions. We show theoretically that the beam radius exhibits oscillations along the propagation axis at the steady state, or at a given point during the transit time. These characteristics result from the nonlocality of the nonlinear process. We discuss the experimental conditions for observing these oscillations. Similar behaviors can be predicted in nonlinearities induced by other non local effects.
... A deacetylation degree of 84% was measured according to Brugnerotto's method... more ... A deacetylation degree of 84% was measured according to Brugnerotto's method, using FTIR spectroscopy.(29) The average viscosimetric molecular weight (M v = 1.0 × 10 6 g/mol) was determined by capillary viscosimetric measurements using the experimental conditions of ...
Micelle formation was followed by micro-DSC and rheology for aqueous solutions of two copolymers ... more Micelle formation was followed by micro-DSC and rheology for aqueous solutions of two copolymers of PEO-PPO-PEO, the Pluronic F127 (from BASF) and the EG56 (from PolymerExpert), a branched copolymer built with three chains of F127 type. It is shown that micellization is endothermic and that, for both polymers, the enthalpy of formation/melting is proportional to total concentration. The rheology of the solutions was carefully analyzed, before gelation for F127, and it reveals firstly the progressive changes of solubility of the unimers (decease of relative solution viscosity), followed by micelle formation over a 10 • C range. In this range, the micelle concentration dependence on temperature was deduced from enthalpy measurements and the corresponding volume fractions were derived. Viscosity was interpreted within the framework of well-known theories for hard sphere suspensions (Krieger-Dougherty or Quemada) based on an analogy between micelles and nanosized hairy grain suspensions. The gel state is achieved due to formation of the colloidal crystal. For EG56, the rheology is quite different; as the aggregation increases with temperature, a progression is observed from Newtonian to visco-elastic liquid. The characteristic frequency, defined by the relation G = G , for EG56 varies with temperature and the corresponding times increase by two orders of magnitude according to an Arrhenius law. The frequency dependence of G and G at different temperatures can be superposed with a horizontal shift factor and a small amplitude adjustment. There is no elastic solid formation in this case. The "gelation" of these two copolymers is compared to the physical gelation of cold-set gels (gelatin).
ABSTRACT Extensive dielectric measurements in the frequency range 100 kHz–15 GHz have been perfor... more ABSTRACT Extensive dielectric measurements in the frequency range 100 kHz–15 GHz have been performed at 25 °C on two oil-continuous microemulsion systems composed of water, n-dodecane, 1-pentanol, sodium dodecylsulfate and water, toluene, 1-butanol, sodium dodecylsulfate. It was found that in the above mentioned systems, the micellar phases display broad dielectric relaxation spectra which imply different dielectric processes. Two processes, occurring in the low frequency region around 1 and 100 MHz seem to be of ionic origin. They can be attributed to Maxwell–Wagner effect for heterogenous systems and the counterion movement in the interfacial layer around the micelles. The relaxation observed in the high frequency range (1 GHz) could possibly be attributed to the presence of water and alcohol in the vicinity of the reverse micellar surface. The strength of the dielectric relaxation process in the very high frequency region of about 16 GHz is dependent on the water content and is possibly related to pure water outside the interfacial layer.
A strong hysteretic behaviour has been observed for the self-focusing of a c.w. laser beam focuse... more A strong hysteretic behaviour has been observed for the self-focusing of a c.w. laser beam focused in a four-component micellar phase near a sponge phase in the phase diagram. All data demonstrate that the laser wave induces a structural change from the micellar phase towards a phase of droplets the nature of which is discussed. The recorded limit cycles and “creep” of cycles allow an analogy with the magnetization of a ferromagnetic material to be developed.
The aim of the present work is first to synthesis a magnetic chitosan hydrogel (chitosan ferrogel... more The aim of the present work is first to synthesis a magnetic chitosan hydrogel (chitosan ferrogel) using the blending method and second to study it rheological behavior. Magnetic components ( maghemite particles γ-Fe2O3 ) were synthesized via a simple chemical co-precipitation route also called Massart's procedure. Before being dispersed in chitosan network, γ-Fe2O3 particles were covered with a cationic polyelectrolyte (Polydiallyldimethylammonium chloride; PDADMAC) and the exact quantity required to cover the entire surface of maghemite particles was determined by Electrophoretic mobility. The successful functionalization of maghemite particles was confirmed by zeta potential measurement. The prepared ferrogel was gelified using glyoxal as crosslinking agent. The effect of continuous magnetic field on rheological properties of the elaborated ferrogel was studied, under controlled temperature before and after the gelation process, using a rotating rheometer fitted with a new ma...
Regeneration of thixotropic gels resulting from aggregation of positively charged magnetic nanopa... more Regeneration of thixotropic gels resulting from aggregation of positively charged magnetic nanoparticles is here investigated by mechanical spectroscopy. The frequency independence of the ratio G /G (G and G being respectively the viscous and the elastic moduli) at the gel point seen as a liquidsolid transition allows the determination of the gelation time t g and of the power law exponent on the angular frequency for both moduli (G ∼ ω , G ∼ ω ). This behaviour is similar to the one observed for classical chemical and physical gels. It implies a broad relaxation time spectrum which is compatible with previous dynamic magneto-optical birefringence measurements. The value of t g decreases exponentially with an increase of the pH that controls the interactions between particles through their surface density of charges. In contrast, the relaxation exponent is found to be nearly insensitive to the pH. A fractal dimension of 2.07 ± 0.06 is deduced from the power law exponent at the gelat...
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