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Surface behavior of poly (epsilon-caprolactone) (PCL) have been studied at the air/water interface (A/W). PCL is a hydrophobic and crystalline polyester with a glass transition temperature around -60 degrees centigrade, a melting point around 55 degrees centigrade, excellent biocompatibility, and low toxicity. In the past decade, PCL based systems have attracted considerable interest for controlled-release drug delivery and as scaffolds for tissue engineering, that require a fundamental understanding of PCL's degradation mechanisms and crystallization properties. PCL spherulites were commonly observed in previous bulk studies. This thesis focuses on PCL crystallization in Langmuir monolayers. Brewster angle microscopy (BAM) studies show that square, distorted rectangular, and dendritic crystals form at the A/W interface. While dendritic structures have been observed in poly (ethylene oxide) (PEO) thin film on solid substrates, this study of PCL is the first time that dendritic morphologies have been observed at the A/W interface for a linear flexible-coil polymer. As far as we know, the crystallization of flexible-coil polymers at the A/W interface is a brand new area of research. These findings may provide an interesting model system for studying crystallization in confined geometries and the effect of crystallinity on enzyme catalyzed hydrolysis of this important biodegradable polymer at the A/W interface. The main objectives of this thesis were to investigate the phase behavior of PCL at the A/W interface, gain a deeper understanding of the nucleation and growth mechanism of PCL crystallization at the A/W interface through surface pressure-area isotherms and isobaric area relaxation analyses, and interpret the effects of molecular weight on the nucleation and growth mechanism, and morphologies of semicrystalline PCL crystallized in Langmuir monolayers at the A/W interface. / Master of Science

Polyhedral oligomeric silsesquioxanes (POSS) have attracted substantial academic interest for many years as hybrid materials and nanofillers for controlling thermal and mechanical properties, and providing thermal and chemical resistance while retaining ease of processing. A natural extension of these studies has been POSS-based amphiphiles and thin film coatings. Studies at the air/water (A/W) interface have shown that trisilanol-POSS derivatives are amphiphilic and form uniform Langmuir films, whereas closed-cage POSS derivatives are hydrophobic and aggregate. In previous work, a triester (POSS-triester) and a triacid (POSS-triacid) were synthesized from PSS-(3-hydroxypropyl)-heptaisobutyl (POSS-OH) and Weisocyanate and fully characterized by surface pressure – area per molecule (Π-A) isotherm and Brewster angle microscopy (BAM) studies at the A/W interface. The results indicated that POSS-triester is surface active forming a liquid expanded (LE) monolayer, whereas POSS-triacid forms a liquid condensed (LC) monolayer that is only weakly affected by pH. A face-on conformation was proposed and examined to understand the packing of POSS-based amphiphilic molecules at the A/W interface. The face-on/vertex-on comparison is rarely discussed for Langmuir monolayers at the A/W interface. In this thesis, three other POSS-based esters were synthesized from POSS-OH and aminopropylisobutyl-POSS (POSS-NH₂) using Weisocyanate and a similar isocyanate containing two tert-butyl protected carboxylic acids. The synthesized materials are characterized by Π-A isotherm and BAM. For POSS-OH based diester (PAlDE) and POSS-NH2 based diester (PAmDE), LE/LC phase transitions were observed in Π-A isotherms over part of the experimentally accessible temperature range and were attributed to a change from a vertex-on to face-on conformation. Apparent BAM images confirmed LC islands coexisted with the LE phase. The experimentally observed dynamic estimates of the critical temperatures (Tc) were estimated from a two-dimensional Clausius-Clapeyron analysis and were consistent with the temperature dependence of the Π-A isotherms. These LE/LC phase transitions are the first observed for POSS amphiphiles. / Ph. D.

Polyhedral oligomeric silsesquioxanes (POSS) have attracted substantial academic interest for many years as hybrid materials and nanofillers for controlling thermal and mechanical properties, and for providing thermal and chemical resistance while retaining ease of processing. A natural extension of these studies has been working on POSS-based amphiphiles and thin film coatings. Studies at the air/water (A/W) interface have shown that trisilanol-POSS derivatives are amphiphilic and form uniform Langmuir films, whereas closed-cage POSS derivatives are hydrophobic and aggregate. In this study, two novel POSS derivatives were synthesized from PSS-(3-hydroxypropyl)-heptaisobutyl substituted (POSS-OH) and completely characterized. Weisocyanate reacted with POSS-OH, and a POSS-based triester (POSS-triester) was obtained. Trifluoroacidolysis of the POSS-triester at room temperature afforded the corresponding triacid (POSS-triacid). Purified POSS-OH, POSS-triester, and POSS-triacid were studied by using surface pressure - area per molecule (? -A) isotherms as well as Brewster angle microscopy (BAM) at the air/water (A/W) interface. Compared with previous work on trisilanol-POSS derivatives, the results indicated that POSS-triester was surface active and formed a liquid-expanded (LE) monolayer. In contrast, POSS-triacid monolayers were more condensed (LC) and were not dramatically affected by changes in pH. Results for the lift-off areas (Alift-off), limiting areas (A0), collapse areas (Ac), and collapse pressures (? c) of POSS-OH, POSS-triester, and POSS-triacid were compared to trisilanolisobutyl-POSS (TiBP) and were interpreted in terms of possible molecular conformations. Whereas, TiBP has been hypothesized to exist in a vertex-on conformation, POSS-OH and POSS-triacid packing at the A/W interface was consistent with face-on conformations. For POSS-triester, the isotherm was consistent with a vertex-on conformation at low ? , but a face-on conformation at high ? . / Master of Science

Ce travail a porté sur l'étude des propriétés des monocouches de copolymères diblocs neutres-chargés de poly(tert-butylstyrène)/poly(styrène sulfonate) à l'interface eau/air. Conformément aux modèles théoriques, l'étude des isothermes de compression des monocouches a permis de montrer que les chaînes chargées ancrées à l'interface ont une conformation de type brosse osmotique aux aires moléculaires étudiées. Nous montrons aussi l'importance du solvant d'étalement sur les isothermes de pression de surface et une restructuration de l'interface à forte compression qui apparaît sous la forme d'une relaxation de la pression de surface. Les observations de la monocouche par microscopie à l'angle de Brewster et diffusion de rayons X ont révélé l'existence d'une instabilité de flambage de l'interface. Lors de sa compression, l'interface se déforme et laisse apparaître des structures de grandes dimensions (5 à 35 micromètres), aisément observables malgré leur faible amplitude (quelques nanomètres). Nous avons montré que l'apparition du flambage résulte d'un échange de molécules entre l'interface et la sous-phase. Nous avons proposé différents mécanismes de déformation de la monocouche qui permettent de rendre compte qualitativement des différentes caractéristiques du flambage comme la dépendance de la taille des structures avec l'épaisseur de la monocouche, la dépendance de la pression d'apparition des structures avec la concentration en copolymère dans la sous-phase et l'insensibilité au sel. L'impossibilité de mesurer directement l'amplitude des structures à l'interface nous a conduit à développer une nouvelle méthode d'observation des monocouches à l'interface eau/air au moyen d'un microscope à force atomique. Les résultats obtenus sur différentes couches à l'interface eau/air montrent ainsi toutes les potentialités de cette nouvelle technique dans l'observation de monocouches présentant des domaines de taille inférieure à 100 nm.

Orientador: Victor Ciro Solano Reynoso / Banca: Keizo Yukimitu / Banca: Raul Fernando Cuevas Rojas / Resumo: O presente trabalho visou a produção e o estudo das propriedades físicas de amostras de resina epóxi transparente dopadas com diferentes concentrações de nanocristais de sulfeto de cádmio (CdS). As técnicas de difração de raios-X, espectroscopia no infravermelho, espectroscopia Raman e calorimetria diferencial de varredura (DSC) foram utilizadas para estudar as propriedades estruturais. Espectroscopias de refletância e de transmitância foram utilizadas para obter a dispersão do índice de refração e do coeficiente de extinção na região do UV-Vis para amostras dopadas com diferentes concentrações de CdS. A técnica do ângulo de Brewster foi também utilizada para determinar o índice de refração das diferentes amostras. Os valores dos índices de refração obtidos através das medidas de refletância e de transmitância na região do UV-Vis e da técnica do ângulo de Brewster foram comparados e os resultados mostraram que a técnica do ângulo de Brewster além de apresentar valores que conferem com a literatura apresentou valores com alta precisão. Foram realizadas medidas de birrefringência opticamente. Foram obtidos resultados da birrefringência fotoinduzida por um fóton para diferentes concentrações de CdS por amostra e para diferentes intensidades da luz de excitação. Os resultados foram quantificados utilizando alguns dos principais modelos teóricos, onde foi observado que a resina epóxi pura apresenta birrefringência fotoinduzida e a adição do CdS contribui para o aumento da birrefringência. / Abstract: The present work sought production and study of the physical properties of samples of transparent epoxy resin doped with different concentrations of structures of cadmium sulfide (CdS) nanocrystals. X-ray diffraction, infrared spectroscopy, Raman spectroscopy e differential scanning calorimetry techniques were used to study their structural properties. Reflectance and transmittance spectroscopy were used to obtain of the refraction index and of the extinction coefficients dispersion in the UVVis region for doped samples with different concentrations of CdS. The Brewster angle technique also was used to determine the refraction index of the different samples. The refraction index values obtained using the reflectance and transmittance measurement in the UV-Vis region and Brewster angle technique were compared and the results showed that the Brewster angle technique besides presents values that check with the literature, presented values with high precision. Measurements of optically induced birefringence were accomplished. Were obtained results of the photo induced birefringence by a photon for different concentrations of CdS for sample and for different intensities of the excitement light. The results were quantified using some of the principal theoretical models, where was observed that the pure epoxy resin presents photo induced birefringence and the addition of the CdS contributes to the increase of the birefringence. / Mestre

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