Uso das técnicas de infravermelho e de ressonância magnética nuclear na caracterização da reação ácido-base de um cimento odontológico experimental

Glass ionomer cements (GICs) are products of the acid-base setting reaction between an finely fluoro-alumino silicate glass powder and poly(acrylic acid) in aqueous solution. The sol gel method is an adequate route of preparation of the glasses used to obtain the GICs. The objective of this paper was to compare two powders: a commercial and an experimental and to investigate the structural changes during hardening of the cements by FTIR and Al MAS NMR. These analyses showed that the experimental glass powder reacted with organic acid to form the GICs and it is a promising material to manufacture dental cements.

Inorganic-Organic Nanocomposite Assembly Using Collagen as a Template and Sodium Tripolyphosphate as a Biomimetic Analog of Matrix Phosphoprotein

Nanocomposites created with polycarboxylic acid alone as a stabilization agent for prenucleation clusters-derived amorphous calcium phosphate exhibit nonperiodic apatite deposition. In the present study, we report the use of inorganic polyphosphate as a biomimetic analog of matrix phosphoprotein for directing poly(acrylic acid)-stabilized amorphous nano-precursor phases to assemble into periodic apatite-collagen nanocomposites. The sorption and desorption characteristics of sodium tripolyphosphate to type I collagen were examined. Periodic nanocomposite assembly with collagen as a template was demonstrated with TEM and SEM using a Portland cement-based resin composite and a phosphate-containing simulated body fluid. Apatite was detected within the collagen at 24 h and became more distinct at 48 h, with prenucleation clusters attaching to the collagen fibril surface during the initial infiltration stage. Apatite-collagen nanocomposites at 72 h were heavily mineralized with periodically arranged intrafibrillar apatite platelets. Defect-containing nanocomposites caused by desorption of TPP from collagen fibrils were observed in regions lacking the inorganic phase.

Characterization and application of nanostructured films containing Au and TiO2 nanoparticles supported in bacterial cellulose

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of the type of phospholipid head and of the conformation of the polyelectrolyte on the growth of calcium carbonate thin films on LB/LbL matrices

Calcium carbonate is one of the most important biominerals, and it is the main constituent of pearls, seashells, and teeth. The in vitro crystallization of calcium carbonate using different organic matrices as templates has been reported. In this work, the growth of calcium carbonate thin films on special organic matrices consisting of layer-by-layer (LbL) polyelectrolyte films deposited on a pre-formed phospholipid Langmuir-Blodgett (LB) film has been studied. Two types of randomly coiled polyelectrolytes have been used: lambda-carrageenan and poly(acrylic acid). A precoating comprised of LB films has been prepared by employing a negatively charged phospholipid, the sodium salt of dimyristoilphosphatidyl acid (DMPA), or a zwitterionic phospholipid, namely dimyristoilphosphatidylethanolamine (DMPE). This approach resulted in the formation of particulate calcium carbonate continuous films with different morphologies, particle sizes, and roughness, as revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The crystalline structure of the calcium carbonate particles was analyzed by Raman spectroscopy. The randomly coiled conformation of the polyelectrolytes seems to be the main reason for the formation of continuous films rather than CaCO3 isolated crystals. (C) 2012 Elsevier B.V. All rights reserved.

Polymerisierbare und polymere Langmuir-Blodgett-Monoschichten zur gezielten Kalziumcarbonatkristallisation an der Luft-Wasser-Grenzfläche

In der vorliegenden Arbeit konnte mit Hilfe von neu synthetisierten Monomeren und Polymeren Kristallisationstemplate für die Kalziumkarbonatkristallisation dargestellt werden. Hierzu wurde zunächst die Phasenseparation des Monomeren und Polymeren mit der nukleationsfördernden Stearinsäure detailliert untersucht und gezeigt, dass die Monomer und Polymer-Mischsysteme auf Ca(HCO3)2-Lsg. perfekt phasenseparieren. Weiter konnte diese entmischte Struktur mit Hilfe von UV-Bestrahlung in der Monoschicht polymerisiert und damit fixiert werden. Des weiteren konnte gezeigt werden, dass die Kristallisation unter den monomeren und polymeren Bereichen vollständig inhibiert wird und ausschließlich unter den Stearinsäuredomänen von statten geht. Das Problem der Kristallisation in die dritte Dimension, also ins Volumen, konnte durch die Zugabe von Polyacrylsäure zur Subphase kontrolliert werden, so dass nun eine Abbildung der strukturierten Monoschicht durch Kalkkristallisation möglich ist. Im zweiten Teil der Arbeit konnte ein amphiphiles Itaconat synthetisiert werden, welches auf Grund seiner Carbonsäurefunktion ebenfalls nukleationsfördernd wirkt. Auch hier war es möglich die Monoschicht zu polymerisieren. Weiter konnte erneut gezeigt werden, dass es möglich ist mit Hilfe von Polyacrylsäurezusatz die interne Struktur der Membran als Templat für die Kristallisation zu nutzen, so dass auch dieses System zur gezielten Kalkkristallisation genutzt werden kann.

Nicht-wässrige Emulsionen zur Erzeugung neuer Nanopartikel

In der eingereichten Arbeit wurde die Nutzung von nicht-wässrigen Emulsionen, bestehend aus zwei organischen, aprotischen Lösungsmitteln, zur Erzeugung verschiedener polymerer Nanopartikel beschrieben. Diese Zweiphasenmischungen und die Verwendung maßgeschneiderter Emulgatoren bestehend aus Poly(isopren-block-methylmethacrylat) ermöglichten den Zugang zu einer Vielzahl an Reaktionen und Prozessen, welche in wässrigen Emulsionen bisher nicht oder nur schwer möglich waren. Die Generierung von Partikeln auf Basis katalytischer Polymerisationen erfolgte unter Verwendung der Ringöffnenden Metathese-Polymerisation (ROMP), der Acyclischen Dien-Metathese-Polymerisation (ADMET), der Cyclopolymerisation von α,ω-Diinen und der Ni-katalysierten Polymerisation von Isocyaniden. Mittels ROMP konnten stabile Dispersionen erzeugt werden, welche Partikel mit verschiedensten Molekulargewichten, Größen und Morphologien enthielten. Diese Eigenschaften konnten durch die Wahl des Monomers, die Katalysatorkonzentration oder den Emulgatortyp beeinflusst werden. Des Weiteren wurden Partikel mit komplexen Morphologien wie Kern-Schale-Strukturen synthetisiert. Dazu erfolgte die Generierung von Partikeln aus Poly(urethan) oder Poly(norbornenderivaten), welche in situ und ohne intermediäre Aufarbeitung mit einer Schale aus Poly(methacrylat) versehen wurden. Der Nachweis dieser Strukturen gelang mittels verschiedener Schwermetall-Markierungsverfahren in der Transmissionselektronenmikroskopie. Schlussendlich erfolgte die Herstellung von hochvernetzten und molekular geprägten Poly(acrylsäure)-Partikeln. Hierbei wurden unterschiedliche pharmakologische Wirkstoffe und Farbstoffe in die Partikel eingebracht, um deren Migrationsverhalten und Wiederanbindung an die Partikel zu untersuchen. Weiterhin wurden die Partikel erfolgreich in Zellaufnahmeexperimenten eingesetzt.

Fluorenbasierende amphiphile Kammpolymere zur Ausbildung definierter Strukturen an Oberflächen und in Lösungen

Die Dissertation beschreibt die Darstellung und Charakterisierung von neuartigen, amphiphilen Carbazol- und Fluoren-(co)-polymeren, die infolge ihres strukturellen Aufbaus sowohl selbstorganisierende als auch optoelektronische Eigenschaften kombinierten. Zum einen wurden Kammpolymere mit konjugierten, steifen Rückgraten und flexiblen sowie konformativ schaltbaren Polyelektrolytseitenketten dargestellt und auf eine pH-abhängige Selbstorganisation in Lösung und an Oberflächen untersucht. Des Weiteren wurden neutrale, methanollösliche Polyfluorene synthetisiert, die in Kombination mit einem unpolaren Polyindenofluorenderivat zum Aufbau mehrschichtiger PLEDs mittels nasschemischer Verfahren eingesetzt wurden. Zum anderen fand die Synthese von amphiphilen Polyfluorenen statt, die als Emulgatoren zur Stabilisierung von inversen Emulsionen eingesetzt wurden. Dabei konnten mit Hilfe eines bereits für die Darstellung von anorganisch-organischen Kern-Schale-Partikeln etablierten in situ-Verfahrens formanisotrope, kristalline Zinkoxidkerne mit konjugierter Polymerhülle erhalten werden.

Synthesis of gadolinium-labeled shell-crosslinked nanoparticles for magnetic resonance imaging applications

Shell-crosslinked knedel-like nanoparticles (SCKs; knedel is a Polish term for dumplings) were derivatized with gadolinium Shell chelates and studied as robust magnetic-resonance-imaging-active structures with hydrodynamic diameters of 40 +/- 3 nm. SCKs possessing an amphiphilic core-shell morphology were produced from the aqueous assembly of diblock copolymers of poly(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA(52)-b-PMA(128), and subsequent covalent crosslinking by amidation upon reaction with 2,2'-(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non-toxicity towards mammalian cells, non-immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with Gd-III and designed for potential use as a unique nanometer-scale contrast agent for MRI applications is described herein. Utilization of an amino-functionalized diethylenetriaminepentaacetic acid-Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39 s(-1) mM(-1)) in an applied magnetic field of 0.47 T at 40 degrees C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20 000 s(-1) mM(-1)).

BLOCK COPOLYMERS CONTAINING A LOW-SURFACE-ENERGY BLOCK AND THEIR APPLICATIONS

This thesis reports the synthesis and/or applications of three types of block copolymers that each bear a low-surface-energy block. First, poly(dimethylsiloxane)-block-poly(2-cinnamoyloxyethyl acrylate) (PDMS-b-PCEA) was synthesized and characterized. Cotton coating using a micellar solution of this block copolymer yielded superhydrophobic cotton fabrics. X-ray photoelectron spectroscopy (XPS) and surface property analyses indicated that the PDMS block topped the polymer coating. Photocuring the cotton swatches crosslinked the underlying PCEA layer and yielded permanent coatings. More interestingly, hydrophilically patterned superhydrophobic cotton fabrics were produced using photolithography that allowed the crosslinking of the coating around irradiated fibers but the removal, by solvent extraction, of the coating on fibers that were not irradiated. Since water-based ink only permeated the uncoated regions, such patterned fabric was further used to print ink patterns onto substrates such as fabrics, cardboard, paper, wood, and aluminum foil. Then, another PDMS-based diblock copolymer poly(dimethylsiloxane)-block-poly(glycidyl methacrylate) (PDMS-b-PGMA) was prepared. Different from PCEA that photocrosslinked around cotton fibers, PGMA reacted with hydroxyl groups on cotton fiber surfaces to get covalently attached. Further, different PGMA chains crosslinked with each other. PDMS-b-PGMA-coated cotton fabrics have been used for oil-water separations. In addition, polymeric nanoparticles were grafted onto cotton fiber surface before PDMS-b-PGMA was used to cover the surfaces of the grafted spheres and the residual surfaces of the cotton fibers. These two types of fabrics, coated by the block copolymer alone or by the polymer nanospheres and then the copolymer, were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), and water repellency analyses. A comprehensive comparative study was made of their performances in oil-water separation. Finally, a fluorinated ABC triblock copolymer poly(acrylic acid)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(2-perfluorooctylethyl methacrylate) (PAA-b-PCEMA-b-PFOEMA) was used to iii encapsulate air nanobubbles. The produced air nanobubbles were thermodynamically stable in water and were some 100 times more stable than commercially available perfluorocarbon-filled microbubbles under ultrasound. These nanobubbles, due to their small sizes and thus ability to permeate the capillary networks of organs and to reach tumors, may expand the applications of microbubbles in diagnostic ultrasonography and find new applications in ultrasound-regulated drug delivery.

CONTROL OF SIZE AND MAGNETIC PROPERTIES OF CARBOXYL-FUNCTIONALIZED MAGNETITE PARTICLES: SYNTHESIS PROCEDURES, CHARACTERIZATIONS, AND APPLICATIONS

Magnetic nanoparticles (MNPs) are known for the unique properties conferred by their small size and have found wide application in food safety analyses. However, their high surface energy and strong magnetization often lead to aggregation, compromising their functions. In this study, iron oxide magnetic particles (MPs) over the range of nano to micro size were synthesized, from which particles with less aggregation and excellent magnetic properties were obtained. MPs were synthesized via three different hydrothermal procedures, using poly (acrylic acid) (PAA) of different molecular weight (Mw) as the stabilizer. The particle size, morphology, and magnetic properties of the MPs from these synthesis procedures were characterized and compared. Among the three syntheses, one-step hydrothermal synthesis demonstrated the highest yield and most efficient magnetic collection of the resulting PAA-coated magnetic microparticles (PAA-MMPs, >100 nm). Iron oxide content of these PAA-MMPs was around 90%, and the saturation magnetization ranged from 70.3 emu/g to 57.0 emu/g, depending on the Mw of PAA used. In this approach, the particles prepared using PAA with Mw of 100K g/mol exhibited super-paramagnetic behavior with ~65% lower coercivity and remanence compared to others. They were therefore less susceptible to aggregation and remained remarkably water-dispersible even after one-month storage. Three applications involving PAA-MMPs from one-step hydrothermal synthesis were explored: food proteins and enzymes immobilization, antibody conjugation for pathogen capture, and magnetic hydrogel film fabrication. These studies demonstrated their versatile functions as well as their potential applications in the food science area.

Temperature-and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

Temperature-and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

Toughening effects of poly(butylene terephthalate) with blocked isocyanate-functionalized poly(ethylene octene)

BACKGROUND: Blocked isocyanate-functionalized polyolefins have great potential for use in semicrystalline polymer blends to obtain toughened polymers. In this study, poly(butylene terephthalate) (PBT) was blended with allyl N-[2-methyl-4-(2-oxohexahydroazepine-1 -carboxamido)phenyl] carbamate-functionalized poly(ethylene octene) (POE-g-AMPC).RESULTS: New peaks at 2272 and 1720 cm(-1), corresponding to the stretching vibrations of NCO and the carbonyl of NH-CO-N, respectively, in AMPC, appeared in the infrared spectrum of POE-g-AMPC. Both rheological and X-ray photoelectron spectroscopy results indicated a new copolymer was formed in the reactive blends. Compared to uncompatibilized PBT/POE blends, smaller dispersed particle sizes with narrower distribution were found in the compatibilized PBT/POE-g-AMPC blends. There was a marked increase in impact strength by about 10-fold over that of PBT/POE blends with the same rubber content and almost 30-fold higher than that of pure PBT when the POE-g-AMPC content was 25 wt%.

Isothermal Crystallization Behavior of Poly(L-lactic acid)/Organo-Montmorillonite Nanocomposites

The isothermal crystallization behavior of poly(L-lactic acid)/organo-montmorillonite nanocomposites (PLLA/OMMT) with different content of OMMT, using a kind of twice-functionalized organoclay (TFC), prepared by melt intercalation process has been investigated by optical depolarizer. In isothermal crystallization from melt, the induction periods (t(i)) and half times for overall PLLA crystallization (100 degrees C <= T-c <= 120 degrees C) were affected by the temperature and the content of TFC in nanocomposites. The kinetic of isothermal crystallization of PLLA/TFC nanocomposites was studied by Avrami theory. Also, polarized optical photomicrographs supplied a direct way to know the role of TFC in PLLA isothermal crystallization process. Wide angle X-ray diffraction (WAXD) patterns showed the nanostructure of PLLA/TFC material, and the PLLA crystalline integrality was changed as the presence of TFC. Adding TFC led to the decrease of equilibrium melting point of nanocomposites, indicating that the layered structure of clay restricted the full formation of crystalline structure of polymer.

Crystallization Behavior and Mechanical Properties of Crosslinked Plasticized Poly(L-lactic acid)

Enhancing the stability of plasticized poly(L-lactic acid) (PLLA) with poly (ethylene glycol) (PEG) is necessary for its practical application. In this study, plasticized PLLA (PLLA/PEG 80/20 wt/wt) was crosslinked under I-ray (Co-60) in the presence of triallyl isocyanurate (TALC) as crosslinking agent. FTIR analysis revealed that PLLA, PEG, and TALC formed a cocrosslinking structure. Crystallization behavior and mechanical properties of the crosslinked plasticized PLLA were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and tensile tests. Experimental results indicated that the crystallization behaviors of both PEG and PLLA in the blends were restrained after irradiation. The melting peak of PEG in the crystallized samples disappeared at a low irradiation doses about 10 kGy. Although PLLA still owned the behavior of crystallize, its cold crystallization temperature and glass transition temperature shifted to higher temperature. Mechanical properties of the plasticized PLLA were strengthened through crosslinking. Both yield strength and elastic modulus of the samples increased after crosslinking.