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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Estudo de sistema micelares em misturas de água/acetonitrila / Studies micellar systems in mixtures of water/acetonitrile

Yihwa, Chang 18 August 2000 (has links)
Neste trabalho, estudou-se o efeito da adição de acetonitrila nas propriedades de micelas do detergente aniônico, dodecil sulfato de sódio (SDS), e do detergente catiônico, cloreto de hexadeciltrimetilamônio (CTACl). Medidas de condutividade foram utilizadas para determinar a concentração micelar crítica, cmc, e o grau de dissociação, α, das micelas em função da fração molar de acetonitrila, XAc. Medidas de supressão de fluorescência, resolvida no tempo, com pireno como sonda, foram utilizadas para determinar a influência de acetonitrila no número de agregação das micelas, N, e na dinâmica de migração de solutos entre as fases aquosa e micelar. Em baixas frações molares XAc < 0,2), a acetonitrila insere-se nas cavidades da água, quebrando parcialmente as pontes de hidrogênio da água com a formação de novas pontes de hidrogênio entre as moléculas de acetonitrila e as moléculas de água. Nesta faixa de concentração, ocorre um aumento da cmc e do α, acompanhada de uma diminuição de N. Observa-se também alterações na dinâmica da interação de contra-íons e co-íons supressores na micela. Assim, as micelas de SDS e CTACl formadas em misturas acetonitrila-água são menores, mais dissociadas e apresentam maior fluidez interna. Ao redor de XAc = 0,2, as misturas de água-acetonitrila tornam-se microheterogêneos com o aparecimento de microdomínios ricos em acetonitrila e microdomínios ricos em água. A proporção das regiões ricas em acetonitrila aumenta com o aumento da fração molar de acetonitrila, com apenas pequenas modificações das propriedades dos dois tipos de microdomínios. Em XAc > 0,2 a variação de cmc e de α com a XAc passa a ser menos acentuada, sugerindo que o detergente forma agregados preferencialmente nas regiões mais aquosas; a sonda fluorescente pireno começa sair das micelas durante o tempo de vida do estado excitado; e há claras mudanças na dinâmica de incorporação de íons nos agregados. / This work presents a study of the effect of added acetonitrile on the properties of the micelles of the anionic detergent sodium dodecylsulfate (SDS) and the cationic detergent hexadecyltrimethylammonium chloride (CTACl). Conductimetric measurements were employed to determine the critical micelle concentration, cmc, and the degree of counterion dissociation, α, of the micelles as a function of the mole fraction of added acetonitrile, XAc. Time resolved fluorescence quenching measurements with pyrene as probe were employed to determine the effect of acetonitrile on the micellar aggregation number, N, and the dynamics of solute migration between the micellar and aqueous phases. At low mole fractions (XAc < 0.2), acetonitrile inserts into the cavities present in liquid water, partially disrupting the hydrogen bonding of water, with formation of new hydrogen bonds between water and acetonitrile. In this range, both the cmc and α increase, while N decreases. The dynamics of incorporation of counterionic and coionic quenchers into the micelles is also altered. Thus, the SDS and CTACl micelles formed in these acetonitrile-water mixtures are smaller, more highly dissociated and internally more fluid than those in aqueous solution. Above XAc of ca. 0,2, acetonitrile-water mixtures become microheterogeneous, the solution containing microdomains rich in acetonitrile and microdomains rich in water. The proportion of acetonitrile-rich microdomians increases with increasing XAc, with only small changes in the properties of the two types of microdomains. Correspondingly, at XAc > > ca. 0.2: the variation of the cmc and α with XAc is much less pronounced, suggesting that the detergent forms aggregates preferentially in the aqueous-rich domains; the fluorescence probe pyrene begins to exit the micelles during its excited state lifetime; and there are distinct changes in the rate constants for the incorporation of ions into the micelles.
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192

Interaction et structure de copolymères neutres-chargés dissymétriques en solution aqueuse

Muller, François 01 December 2000 (has links) (PDF)
Nous avons étudié les propriétés volumiques de copolymères diblocs neutres-chargés dissymétriques. Ces molécules sont composées d'une courte partie neutre de poly(éthylène propylène) (PEP) ou de poly(tert-butyl styrène) (PtBs), et d'une longue partie chargée (polyélectrolyte) poly(styrène sulfonate) sodium (PSSNa) de taux de sulfonation supérieur à 80. Des expériences de diffusion de neutrons aux petits angles et de diffusion quasi-élastique de la lumière ont montré que ces copolymères s'auto-assemblent en solution aqueuse en micelles sphériques : coeur composé de l'auto-association des parties neutres en mauvais solvant, duquel émergent les parties chargées en une grande couronne qui peut être vue comme une brosse polyélectrolyte en géométrie sphérique. La forme et la taille des coeurs hydrophobes ont été trouvées invariantes en fonction de la concentration en polymère et de la concentration en électrolyte ajouté (sel monovalent, NaCl). Cette invariance a permis de déterminer les facteurs de structure des solutions (images des interactions) : les interactions électrostatiques ordonnent les solutions même dans le régime dilué (régime sans contact entre micelles). Dans le régime dilué sans sel ajouté, les parties polyélectrolytes (composant la couronne micellaire) ont été trouvées avec une conformation étendue (quasi-bâtons). Avec du sel ajouté, cette conformation devient de plus en plus flexible dès que la concentration en sel est supérieure à la concentration interne en sel d'une micelle. Dans le régime concentré sans sel ajouté, l'apparition d'un pic polyélectrolyte aux petites échelles, typique de la formation d'un semi dilué de polyélectrolytes, a été mise en évidence. De manière surprenante, cet ordre polyélectrolyte coexiste avec l'ordre entre micelles. L'influence du nombre de chaîne par micelle (nombre d'agrégation) a été discutée. Avec du sel ajouté, le pic polyélectrolyte disparaît, tandis que les solutions restent ordonnées. La distribution des contre-ions a été étudiée par des expériences de diffusion de rayons x aux petits angles. Les contre-ions Na+ ont été remplacés par d'autres contre-ions (typiquement Cs+ et TMA+) par dialyse des solutions. Dans le cas des micelles de faible nombre d'agrégation, la distribution des contre-ions a été trouvée en accord avec la distribution donnée par l'équation de Poisson-Bolztmann autour d'un bâton. Dans le cas des micelles de grand nombre d'agrégation, une forte corrélation entre contre-ions, due au recouvrement des différents nuages, a été mise en évidence. Enfin, la concentration micellaire critique (concentration à partir de laquelle des micelles existent) et l'équilibre des solutions ont été étudiés par électrophorèse capillaire. Les résultats ne sont pas encore bien compris : il existe, quelle que soit la concentration en polymère, 20% de chaînes libres (non associées en micelles).
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193

Diffusionsuntersuchungen an (polymer-modifizierten) Mikroemulsionen mittels Feldgradientenimpuls-NMR-Spektroskopie / Diffusion studies in (polymer-modified) microemulsions using pulsed field gradient NMR spectroscopy

Wolf, Gunter January 2005 (has links)
Aufgrund des großen Verhältnisses von Oberfläche zu Volumen zeigen Nanopartikel interessante, größenabhängige Eigenschaften, die man im ausgedehnten Festkörper nicht beobachtet. Sie sind daher von großem wissenschaftlichem und technologischem Interesse. Die Herstellung kleinster Partikel ist aus diesem Grund überaus wünschenswert. Dieses Ziel kann mit Hilfe von Mikroemulsionen als Templatphasen bei der Herstellung von Nanopartikeln erreicht werden. Mikroemulsionen sind thermodynamisch stabile, transparente und isotrope Mischungen von Wasser und Öl, die durch einen Emulgator stabilisiert sind. Sie können eine Vielzahl verschiedener Mikrostrukturen bilden. Die Kenntnis der einer Mikroemulsion zugrunde liegenden Struktur und Dynamik ist daher von außerordentlicher Bedeutung, um ein gewähltes System potentiell als Templatphase zur Nanopartikelherstellung einsetzen zu können.<br><br> In der vorliegenden Arbeit wurden komplexe Mehrkomponentensysteme auf der Basis einer natürlich vorkommenden Sojabohnenlecithin-Mischung, eines gereinigten Lecithins und eines Sulfobetains als Emulgatoren mit Hilfe der diffusionsgewichteten 1H-NMR-Spektroskopie unter Verwendung gepulster Feldgradienten (PFG) in Abhängigkeit des Zusatzes des Polykations Poly-(diallyl-dimethyl-ammoniumchlorid) (PDADMAC) untersucht. Der zentrale Gegenstand dieser Untersuchungen war die strukturelle und dynamische Charakterisierung der verwendeten Mikroemulsionen hinsichtlich ihrer potentiellen Anwendbarkeit als Templatphasen für die Herstellung möglichst kleiner Nanopartikel.<br><br> Die konzentrations- und zeit-abhängige NMR-Diffusionsmessung stellte sich dabei als hervorragend geeignete und genaue Methode zur Untersuchung der Mikrostruktur und Dynamik in den vorliegenden Systemen heraus. Die beobachtete geschlossene Wasser-in-Öl- (W/O-) Mikrostruktur der Mikroemulsionen zeigt deutlich deren potentielle Anwendbarkeit in der Nanopartikelsynthese. Das Gesamtdiffusionsverhalten des Tensides wird durch variierende Anteile aus der Verschiebung gesamter Aggregate, der Monomerdiffusion im Medium bzw. der medium-vermittelten Oberflächendiffusion bestimmt. Dies resultierte in einigen Fällen in einer anormalen Diffusionscharakteristik. In allen Systemen liegen hydrodynamische und direkte Wechselwirkungen zwischen den Tensidaggregaten vor.<br><br> Der Zusatz von PDADMAC zu den Mikroemulsionen resultiert in einer Stabilisierung der flüssigen Grenzfläche der Tensidaggregate aufgrund der Adsorption des Polykations auf den entgegengesetzt geladenen Tensidfilm und kann potentiell zu Nanopartikeln mit kleineren Dimensionen und schmaleren Größenverteilungen führen. / Owing to their large surface-to-volume ratio nanoparticles show interesting size-dependent properties that are not observable in bulk materials. Thus, they are of great scientific and technological interest. Thereby, the highly desirable preparation of as small particles as possible might be easily achieved using microemulsions as template phases. Microemulsions are thermodynamically stable, transparent and isotropic mixtures of water and oil stabilized by an emulsifying agent. However, microemulsions may form a great variety of different microstructures. Thus, it is of utmost importance to know the underlying microstructure and microdynamics of a chosen microemulsion system in order to use it as a template phase for nanoparticle formation.<br><br> In the present study complex multi-component microemulsion systems based on a naturally occurring soybean lecithin mixture, purified lecithin and sulfobetaine as emulsifiers were investigated by diffusion-weighted pulsed field gradient (PFG) 1H NMR spectroscopy in the presence and absence of the polycation poly-(diallyldimethylammonium chloride) (PDADMAC). The central topic of this study was to structurally and dynamically characterize the present microemulsions with respect to their potential use in nanoparticle formation.<br><br> The concentration- and time-dependent NMR diffusion measurements turned out to be a suitable and accurate tool to investigate the microstructure and microdynamics of the systems under investigation. They reveal closed water-in-oil (W/O) microemulsion microstructures which prove the potential suitability of the respective systems as template phases for the preparation of nano-sized particles. The overall diffusion behavior of surfactants were found to be governed by varying contributions from displacements of entire aggregates, monomer diffusion in the medium and bulk-mediated surface diffusion, respectively. In some cases this led to a marked anomalous diffusion characteristics. In all systems interactions between aggregates are dominated by hydrodynamic and direct forces.<br><br> The addition of PDADMAC to the microemulsion systems results in a stabilization of the liquid interface of surfactant aggregates due to the adsorption of the polycation at the oppositely charged surfactant film and may potentially lead to nanoparticles of smaller dimensions and narrower size distributions.
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194

Polymer self-assembly : adding complexity to mesostructures of diblock copolymers by specific interactions / Polymer self-assembly : adding complexity to mesostructures of diblock copolymers by specific interactions

Schlaad, Helmut January 2005 (has links)
In dieser Arbeit wurde die Rolle selektiver, nicht-kovalenter Wechselwirkungen bei der Selbstorganisation von Diblockcopolymeren untersucht. Durch Einführung elektrostatischer, dipolarer Wechselwirkungen oder Wasserstoffbrückenbindungen sollte es gelingen, komplexe Mesostrukturen zu erzeugen und die Ordnung vom Nanometerbereich auf größere Längenskalen auszuweiten. Diese Arbeit ist im Rahmen von Biomimetik zu sehen, da sie Konzepte der synthetischen Polymer- und Kolloidchemie und Grundprinzipien der Strukturbildung in supramolekularen und biologischen Systemen verbindet. Folgende Copolymersysteme wurden untersucht: (i) Blockionomere, (ii) Blockcopolymere mit chelatisierenden Acetoacetoxyeinheiten und (iii) Polypeptid-Blockcopolymere. / In this work, the basic principles of self-organization of diblock copolymers having the in&#172;herent property of selective or specific non-covalent binding were examined. By the introduction of electrostatic, dipole&ndash;dipole, or hydrogen bonding interactions, it was hoped to add complexity to the self-assembled mesostructures and to extend the level of ordering from the nanometer to a larger length scale. This work may be seen in the framework of biomimetics, as it combines features of synthetic polymer and colloid chemistry with basic concepts of structure formation applying in supramolecular and biological systems. The copolymer systems under study were (i) block ionomers, (ii) block copolymers with acetoacetoxy chelating units, and (iii) polypeptide block copolymers.
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195

Structure-Property Relationships of Surfactants at Interfaces and Polyelectrolyte-Surfactant Aggregates

Kjellin, Mikael January 2002 (has links)
The first part of this thesis is concerned with thestructure-property relationships in nonionic surfactantsystems. The main aim was to investigate how the surfactantstructure influences the adsorption at interfaces andinteractions between surfactant coated interfaces.Particularly, the effect of the structure of the surfactantheadgroups was investigated. These were sugar-based headgroupwith varying size and flexibility and poly(ethylene oxide)based headgroups with or without an additional amide or estergroup. The hydrophobic part of the surfactant consisted mostlyof straight alkyl chains, except for one type of poly(ethyleneoxide) based surfactant with a dehydroabietic hydrophobe. The main technique that was used is the surface forcetechnique, with which the forces acting between two adsorbedsurfactant layers on hydrophilic or hydrophobic surfaces can bemeasured. These forces are important for e.g. the stability ofdispersions. The hydrophilic surfaces employed were glass andmica, whereas the hydrophobic surfaces were silanized glass andhydrophobized mica. The adsorption behavior on hydrophilicsurfaces is highly dependent on the type of headgroup andsurface, whereas similar results were obtained on the two typesof hydrophobic surfaces. To better understand how the surfaceforces are affected by the surfactant structure, measurementsof adsorbed amount and theoretical mean-field latticecalculations were carried out. The results show that the sugarsurfactant layers and poly(ethylene oxide) surfactant layersgive rise to very different surface forces, but that the forcesare more similar within each group. The structure-propertyrelationships for many other physical properties have beenstudied as well. These include equilibrium and dynamicadsorption at the liquid-vapor interface, micelle size, micelledynamics, and wetting. The second part in this thesis is about the aggregationbetween cationic polyelectrolytes and an anionic surfactant.The surface force technique was used to study the adsorption ofa low charged cationic polyelectrolyte on mica, and theaggregation between the adsorbed polyelectrolyte with theanionic surfactant. The aggregation in bulk was studied withturbidimetry, small angle neutron scattering (SANS), and smallangle x-ray scattering (SAXS). An internal hexagonal aggregatestructure was found for some of the bulk aggregates. <b>Keywords:</b>nonionic surfactant, sugar surfactant,poly(ethylene oxide), amide, ester, polyelectrolyte, SDS,hydrophobic surface, glass surface, mica, adsorption,aggregation, micelle size, surface forces, wetting, dynamicsurface tension, NMR, TRFQ, SANS, SAXS, mean-field latticecalculations.
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196

Structure-Property Relationships of Surfactants at Interfaces and Polyelectrolyte-Surfactant Aggregates

Kjellin, Mikael January 2002 (has links)
<p>The first part of this thesis is concerned with thestructure-property relationships in nonionic surfactantsystems. The main aim was to investigate how the surfactantstructure influences the adsorption at interfaces andinteractions between surfactant coated interfaces.Particularly, the effect of the structure of the surfactantheadgroups was investigated. These were sugar-based headgroupwith varying size and flexibility and poly(ethylene oxide)based headgroups with or without an additional amide or estergroup. The hydrophobic part of the surfactant consisted mostlyof straight alkyl chains, except for one type of poly(ethyleneoxide) based surfactant with a dehydroabietic hydrophobe.</p><p>The main technique that was used is the surface forcetechnique, with which the forces acting between two adsorbedsurfactant layers on hydrophilic or hydrophobic surfaces can bemeasured. These forces are important for e.g. the stability ofdispersions. The hydrophilic surfaces employed were glass andmica, whereas the hydrophobic surfaces were silanized glass andhydrophobized mica. The adsorption behavior on hydrophilicsurfaces is highly dependent on the type of headgroup andsurface, whereas similar results were obtained on the two typesof hydrophobic surfaces. To better understand how the surfaceforces are affected by the surfactant structure, measurementsof adsorbed amount and theoretical mean-field latticecalculations were carried out. The results show that the sugarsurfactant layers and poly(ethylene oxide) surfactant layersgive rise to very different surface forces, but that the forcesare more similar within each group. The structure-propertyrelationships for many other physical properties have beenstudied as well. These include equilibrium and dynamicadsorption at the liquid-vapor interface, micelle size, micelledynamics, and wetting.</p><p>The second part in this thesis is about the aggregationbetween cationic polyelectrolytes and an anionic surfactant.The surface force technique was used to study the adsorption ofa low charged cationic polyelectrolyte on mica, and theaggregation between the adsorbed polyelectrolyte with theanionic surfactant. The aggregation in bulk was studied withturbidimetry, small angle neutron scattering (SANS), and smallangle x-ray scattering (SAXS). An internal hexagonal aggregatestructure was found for some of the bulk aggregates.</p><p><b>Keywords:</b>nonionic surfactant, sugar surfactant,poly(ethylene oxide), amide, ester, polyelectrolyte, SDS,hydrophobic surface, glass surface, mica, adsorption,aggregation, micelle size, surface forces, wetting, dynamicsurface tension, NMR, TRFQ, SANS, SAXS, mean-field latticecalculations.</p>
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197

Synthèse et auto-assemblage de copolymères amphiphiles en étoile de type "miktoarm"

Babin, Jerome 20 January 2006 (has links) (PDF)
L'objectif de ce travail est l'étude de l'influence de l'architecture des copolymères à blocs sur les propriétés d'auto-assemblage en solution et en masse. Dans un premier temps, de nouvelles étoiles miktoarm amphiphiles AB2 -à base d'un bloc A hydrophobe de polystyrène et de différents blocs B hydrophiles de poly(acide acrylique), de poly(acide glutamique) et de poly(oxyde d'éthylène)- ont été élaborées en utilisant une stratégie de synthèse originale, fondée sur la combinaison de méthodes de polymérisation « vivante/controlée » et de réactions de modification chimique des bouts de chaîne. Ensuite, nous avons comparé les comportements auto-associatifs en solution diluée des étoiles miktoarm amphiphiles PS-b-(PAA)2 et PS-b-(PGA)2 avec ceux des copolymères à blocs linéaires de même composition. Nous avons également étudié l'effet de deux stimuli externes sur le comportement des objets auto-assemblés : la force ionique et le pH. Enfin, nous avons étudié les propriétés d'auto-organisation à l'état fondu de trois familles de copolymères à blocs : un système « flexible-flexible » PS-b-(PAA)n=1 ;2 et deux systèmes « rigide-flexible » PS-b-(PGA)n=1 ;2 et PS-b-(PBLG)n=1 ;2.
198

Breitbandige Ultraschallabsorptionsspektroskopie an wässrigen ionischen Tensid-Lösungen im Frequenzbereich von 100kHz bis 2GHz / Broadband ultrasonic absorption spectroscopy at ionic surfactants in aqueous solution in the frequency range from 100kHz to 2GHz

Polacek, Rüdiger 12 May 2003 (has links)
No description available.
199

Matériaux hybrides mésoporeux fonctionnalisés par des polymères : élaboration, caractérisation physico-chimique et applications biomédicales / Mesoporous hybrid materials functionalized by polymers : preparation, physicochemical characterization and biomedical applications

Molina, Émilie 10 December 2015 (has links)
Ce travail de thèse porte sur l’élaboration de matériaux siliciques mésostructurés par des agents structurants originaux : les micelles complexes de polyions ou micelles PICs, qui présentent la particularité de s’assembler de façon réversible dans l’eau. Les micelles PICs sont des assemblages formés par interactions électrostatiques entre un copolymère à blocs double-hydrophiles (DHBC) neutre-ionisable et un agent de micellisation de charge opposée au DHBC. Le DHBC utilisé est un poly(oxyde d’éthylène)-b-poly(acide acrylique) POE-b-PAA synthétisé par polymérisation radicalaire contrôlée par transfert d’atome (ATRP) et les agents de micellisation sont commerciaux (oligochitosane OC, antibiotiques aminoglycosides). Tout d’abord, l’influence de divers paramètres (pH, température, concentration) sur les propriétés d’association des micelles PIC a été étudiée en solution aqueuse. Puis, l’influence de ces mêmes paramètres sur la structuration de la silice en présence de complexes de polyions POE-b-PAA/OC a été recherchée, et a permis de mieux appréhender les mécanismes de formation des matériaux hybrides. Il a ainsi été montré qu’en jouant sur les interactions entre les divers constituants, il était possible de contrôler la mésostructure des matériaux (hexagonale, lamellaire, vermiculaire) et leur morphologie (nanoparticules, microparticules). Enfin, la versatilité de l’utilisation de micelles PIC en tant qu’agents structurants de la silice a été mise en évidence avec des systèmes POE-b-PAA/aminoglycosides, qui ont permis d’obtenir directement des matériaux structurés ordonnés chargés en principes actifs. Par ailleurs, les possibilités offertes par l’utilisation des micelles PIC notamment en termes de fonctionnalité et de réversibilité de la micellisation, ont été exploitées et ont permis d’obtenir facilement des matériaux mésoporeux fonctionnalisés par les chaînes ionisables du DHBC, suite à l’extraction sélective de l’agent de micellisation. Il a été montré que de tels matériaux fonctionnels sont capables de complexer des espèces de charges opposées et notamment des principes actifs, qui peuvent par la suite être relargués de façon pH-dépendante. / Mesostructured hybrid materials were prepared by using original silica-structuring agents, which are polyion complex (PIC) micelles. A great advantage of PIC micelles is that they can be reversibly assembled in aqueous solution by varying physico-chemical parameters. PIC micelles are formed by electrostatic complexation between a neutral-anionic double-hydrophilic block copolymer (DHBC) and an oppositely charged agent of micellization; here a poly(ethylene oxide)-b-poly(acrylic acid) PEO-b-PAA (synthesized by controlled radical polymerization by atom transfer ATRP) and commercial polyamines (oligochitosan OC or aminoglycoside antibiotics) were respectively used. First, the influence of various parameters (pH, temperature, concentration) on PIC micelle association properties was investigated in aqueous solution. Then, the effect of these parameters on the silica mesostructuring process was studied, it provides a better understanding of the formation mechanisms. It was shown that varying interactions between constituents allows to control the mesostructure (hexagonal, lamellar, wormlike) and the material morphology (nanoparticle, microparticle). Finally, the versatility of the approach has been demonstrated with PEO-b-PAA/aminoglycoside systems. Drug-loaded ordered mesostructured materials were prepared following a one-pot route. Moreover, taking advantage of the high degree of functionality of DHBC polymers and of the reversibility of the micellization, polyacid-functionalized mesoporous materials were directly prepared by selectively extracting the micellization agent. PAA-functionalized silica materials were then used to complex diverse active entities such as drugs, whose delivery could be pH-controlled.
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200

Estudo de sistema micelares em misturas de água/acetonitrila / Studies micellar systems in mixtures of water/acetonitrile

Chang Yihwa 18 August 2000 (has links)
Neste trabalho, estudou-se o efeito da adição de acetonitrila nas propriedades de micelas do detergente aniônico, dodecil sulfato de sódio (SDS), e do detergente catiônico, cloreto de hexadeciltrimetilamônio (CTACl). Medidas de condutividade foram utilizadas para determinar a concentração micelar crítica, cmc, e o grau de dissociação, &#945;, das micelas em função da fração molar de acetonitrila, XAc. Medidas de supressão de fluorescência, resolvida no tempo, com pireno como sonda, foram utilizadas para determinar a influência de acetonitrila no número de agregação das micelas, N, e na dinâmica de migração de solutos entre as fases aquosa e micelar. Em baixas frações molares XAc &#60; 0,2), a acetonitrila insere-se nas cavidades da água, quebrando parcialmente as pontes de hidrogênio da água com a formação de novas pontes de hidrogênio entre as moléculas de acetonitrila e as moléculas de água. Nesta faixa de concentração, ocorre um aumento da cmc e do &#945;, acompanhada de uma diminuição de N. Observa-se também alterações na dinâmica da interação de contra-íons e co-íons supressores na micela. Assim, as micelas de SDS e CTACl formadas em misturas acetonitrila-água são menores, mais dissociadas e apresentam maior fluidez interna. Ao redor de XAc = 0,2, as misturas de água-acetonitrila tornam-se microheterogêneos com o aparecimento de microdomínios ricos em acetonitrila e microdomínios ricos em água. A proporção das regiões ricas em acetonitrila aumenta com o aumento da fração molar de acetonitrila, com apenas pequenas modificações das propriedades dos dois tipos de microdomínios. Em XAc &#62; 0,2 a variação de cmc e de &#945; com a XAc passa a ser menos acentuada, sugerindo que o detergente forma agregados preferencialmente nas regiões mais aquosas; a sonda fluorescente pireno começa sair das micelas durante o tempo de vida do estado excitado; e há claras mudanças na dinâmica de incorporação de íons nos agregados. / This work presents a study of the effect of added acetonitrile on the properties of the micelles of the anionic detergent sodium dodecylsulfate (SDS) and the cationic detergent hexadecyltrimethylammonium chloride (CTACl). Conductimetric measurements were employed to determine the critical micelle concentration, cmc, and the degree of counterion dissociation, &#945;, of the micelles as a function of the mole fraction of added acetonitrile, XAc. Time resolved fluorescence quenching measurements with pyrene as probe were employed to determine the effect of acetonitrile on the micellar aggregation number, N, and the dynamics of solute migration between the micellar and aqueous phases. At low mole fractions (XAc &#60; 0.2), acetonitrile inserts into the cavities present in liquid water, partially disrupting the hydrogen bonding of water, with formation of new hydrogen bonds between water and acetonitrile. In this range, both the cmc and &#945; increase, while N decreases. The dynamics of incorporation of counterionic and coionic quenchers into the micelles is also altered. Thus, the SDS and CTACl micelles formed in these acetonitrile-water mixtures are smaller, more highly dissociated and internally more fluid than those in aqueous solution. Above XAc of ca. 0,2, acetonitrile-water mixtures become microheterogeneous, the solution containing microdomains rich in acetonitrile and microdomains rich in water. The proportion of acetonitrile-rich microdomians increases with increasing XAc, with only small changes in the properties of the two types of microdomains. Correspondingly, at XAc &#62; > ca. 0.2: the variation of the cmc and &#945; with XAc is much less pronounced, suggesting that the detergent forms aggregates preferentially in the aqueous-rich domains; the fluorescence probe pyrene begins to exit the micelles during its excited state lifetime; and there are distinct changes in the rate constants for the incorporation of ions into the micelles.
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