Estudo de matrizes elastoméricas de borracha natural e PU/PBDO para aplicação tecnológicas

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2014.Esta tese de doutorado aborda estudos relativos à síntese e caracterização de sistemas elastoméricos de borracha natural e uretano/uréia (PU/PBDO) visando aplicações tecnológicas. Foram investigados diferentes compósitos e/ou sistemas elastoméricos. Sendo caracterizado em função da relação elastômero/dopante e/ou funcionalizações específicas. Assim, cada trabalho seguiu objetivos específicos bem definidos para cada compósito e/ou sistema produzido. Dessa forma podemos dividir os trabalhos em dois grandes grupos, um baseado em amostras contendo a borracha natural outro para amostras produzidas com PU/PBDO. Para o grande grupo da borracha natural, investigou-se o efeito de relaxação inversa em filmes finos dopados com moléculas de azocorante produzidos por casting e submetidos ao processo de fotoalinhamento, onde as anisotropias do substrato combinadas ao processo de secagem produzem a orientação das cadeias poliméricas. Em outro trabalho foram investigados os efeitos de diferentes solventes orgânicos na morfologia de membranas de borracha natural utilizando microscopia de força atômica e análises de leis de escala, onde processos experimentais permitiram obter membranas com baixa rugosidade e/ou altamente rugosas, além disso, uma relação da morfologia com a volatilidade dos solventes foi proposta. Visando propósitos biomédicos, blendas de borracha natural com fosfatos de cálcio (Ca/P) foram produzidas e investigadas, onde buscou-se combinar técnicas experimentais de purificação do processo de centrifugação do látex e incorporação de partículas de Ca/P no volume da matriz de borracha. Neste estudo foram analisadas as interações entre proteínas, na forma de vesículas, remanescentes do látex e partículas de Ca/P, onde verificou-se que as partículas de Ca/P são envolvidas pelas vesículas de proteínas dispersas no volume da matriz polimérica. As propriedades ópticas de membranas de borracha natural, pura e dopada com moléculas orgânicas luminescentes, bem como, a produção por eletrofiação de fibras altamente paralelas com diâmetros micro e sub-micrométricos de borracha natural pura e dopada com luminescente também foram investigadas. Por fim, a fabricação e caracterização de eletrodos elastoméricos pela deposição de nanotubos de carbono, por spray ultrassônico, sobre ?substratos? de borracha natural foram estudadas.Para o sistema elastomérico PU/PBDO realizamos os estudos dasxivpropriedades ópticas, morfológicas e mecânicas para membranas dopadas com diferentes moléculas luminescentes, onde a birrefringência para a membrana pura e a emissão polarizada de um luminescente específico para uma membrana dopada foram testadas em função do alinhamento da matriz polimérica devido a deformação mecânica. Esferas luminescentes com uma face enrugada e outra lisa, chamadas de esferas Janus luminescentes, foram produzidas para o sistema PU/PBDO dopado com Alq3 e caracterizadas via técnicas de microscopia (força atômica, eletrônica de varredura e luminescência óptica) e espectroscopia UV-Vis, além disso, para esse mesmo sistema esferas luminescentes micrométricas foram produzidas pela técnica de microfluídica, onde, para ambos os estudos, o controle das condições experimentais foi alcançado. Por fim, a produção e as caracterizações ópticas de esferas de PU/PBDO luminescentes dopadas com diferentes compostos emissores foram investigadas.Abstract : This PhD thesis report the studies carried using as elastomeric materials the natural rubber (NR) and the urethane/urea synthetic elastomer (polyurethane/polybutadienediol - PU/PBDO) for technological applications. Different composites and/or elastomeric systems were investigated and characterized according to the specific elastomer/dopant system and/or due to their added functionalizations. Therefor, this study followed a specific well-defined objectives for each composite system produced. In this way we can divide this PhD thesis in two large groups, one based on samples containing natural rubber and another for samples produced with PU / PBDO. For the large group of natural rubber, we investigated the effect of inverse relation in thin films doped with azo-dye molecules produced by casting and subjected to photoalignment process. Where the anisotropy of the substrates combined with the drying process produces the orientation on the polymer chains. In another study we investigate the effects in the morphology for natural rubber membranes produced using different organic solvents. For this analyses we used the atomic force microscopy (AFM) combinated with scaling laws. This investigation allowed the achievement of membranes with low and/or high roughness. Moreover, we propose the dependence of the morphology due to the volatility of the solvents. In other study, blends of NR with calcium/phosphorous compounds (NR-Ca/P) were produced to be used in biomedical applications. In this study the interactions between NR protein-particles with pseudomicellar form that are remained after latex centrifugation process and Ca/P particles were investigated. Confocal laser scanning microscopy was used to observe these interactions and we can see that the Ca/P particles are involved by the NR protein-particles dispersed in the polymer matrix and a model was proposed to explain that. Optical properties of natural rubber membranes undoped and doped with luminescent organic molecules were investigated. Moreover, highly parallel fibers with diameters in the micro and sub-micrometer range produced by electrospinning from NR solutions undoped and doped with luminescent were also investigated. Finally, were studied the fabrication of elastomeric electrodes produced using NR membranes as substrate and depositing single-walled carbon nanotubes (SWNT) by ultrasonic spray deposition.xviFor the large group of PU/PBDO elastomeric system, we have studied the optical, mechanical and morphological properties of PU/PBDO membranes undoped and doped with luminescent organic molecules. The polarized photoemission for PU/PBDO luminescent membranes were tested on function of the polymer matrix alignment by mechanical deformation. In another study, we investigate the production of luminescent spheres with tuned surface, where one side was wrinkled and other has remained smooth. This spheres are called luminescent Janus spheres and were produced from PU/PBDO system doped with Alq3. Morphological and optical properties were characterized, being determinated the best parameters of the Janus obtention. In addition, micrometer spheres were produced from the same PU/PBDO-Alq3 system using the microfluidics technique, where the diameter sizes of this spheres were changed adjusting the experimental conditions. Finally, we investigate others luminescent compounds for production of new luminescent PU/PBDO spheres

Síntese de nanomateriais calcogênicos (In-Te e Zn-S) e caracterização de suas propriedades físicas: [dissertação]

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2010Os estudos dessa dissertação de mestrado tiveram como objetivos a produção de nanomateriais calcogênicos, dos sistemas In-Te e Zn-S na forma de pó, através da Mecano-Síntese e a caracterização de suas propriedades físicas. Foi observada a potencialidade da Mecano-Síntese na obtenção de fases do diagrama de fases para ambos os sistemas e da fase de alta pressão InTe(II). Foi necessário tempos de moagem curtos ~2h para a formação das fases. As fases obtidas foram InTe tetragonal, InTe cúbica de alta pressão, In4Te3 ortorrômbica, ZnS cúbica do tipo blenda de zinco e ZnS hexagonal do tipo wurtzita. As morfologias e composições químicas dos produtos finais foram analisadas através de microscopia eletrônica de varredura combinada com fluorescência de raios X por dispersão de energia. A difração de raios X foi empregada para acompanhar a evolução estrutural das amostras em função do tempo de moagem, da temperatura e do envelhecimento após a produção. As informações cristalográficas das fases cristalinas identificadas foram obtidas através de análises de Rietveld dos difratogramas experimentais, utilizando o pacote de programas GSAS de distribuição gratuita. Os tamanhos médios de cristalitos das fases obtidas variaram entre 8 e 26 nm, estimados através da combinação das técnicas de difração de raios X e microscopia eletrônica de transmissão de alta resolução. A calorimetria diferencial de varredura foi capaz de mostrar a fusão de Te e In não reagidos e da fase In4Te3,e sugeriu cristalização/relaxamento estrutural e variação no calor específico das fases presentes nas amostras feitas por Mecano-Síntese. Utilizando a espectroscopia Raman foi possível identificar modos vibracionais das fases de Te, ?-TeO2, InTe(I), S e ZnS. As discrepâncias entre os valores de frequência obtidos e os da literatura sugerem condições de tensão/deformação das redes cristalinas presentes nas amostras produzidas por Mecano-Síntese. Os resultados obtidos pelas diferentes técnicas supracitadas possibilitaram uma ampla caracterização das ligas apresentadas nessa dissertação. Até o presente momento, os resultados dos estudos dessa dissertação foram apresentados em 2 congressos nacionais e permitiram a redação/submissão de dois artigos (em avaliação) em revistas internacionais

Latex and natural rubber : recent advances for biomedical applications

Recently, latex (NRL) and natural rubber (NR) from Hevea brasiliensis have emerged as promising biomaterials from renewable sources for biomedical applications. Although some attempts at commercial applications have been made, there is a need to comprehensively document the state-of-the-art of these biopolymers for biomedical applications and regenerative medicine. Here we present the recent advances in the development of NRL and NR as biomedical materials with potential properties including biocompatibility and biodegradability. Due to the angiogenic properties of NRL and NR, well-defined functional materials can be used for drug delivery systems (oral/transdermal), scaffolds for skin and bone regeneration, and dressings for wound healing. The incorporation of drugs, nanoparticles, cells, and others into NRL and NR polymer chains offers a wide range of applications such as dressings with antimicrobial activity and sustained release systems. Concluding remarks on the growth of these biomaterials for biomedical applications and regenerative medicine were discussed

Electrospun natural rubber fibers-based flexible conductive membranes

In recent years, the technique of electrospinning has been used to develop a novel class of micro- and nanoscale materials based on fibrous structures. Several polymers, in particular elastomers, that have been implemented in this process rely on properties such as elasticity, flexibility, biocompatibility, and low cost. Herein, we describe for the first time the electrospinning of natural rubber fibers without polymeric matrix to obtain self-standing non-woven mats and oriented elastomeric fibers. The fibers average diameters were approximately 5.5 µm. Polyaniline (PAni) was deposited on the membrane surface in order to enhance the conductive properties making easy the charge transportation. We have obtained biocompatible and flexible fibrous materials using natural rubber, this research opens up possibilities of using micro and nanofibers of only-natural rubber in many applications including sensors preparation. Keywords: Electrospinning; Fiber technology; Microstructure; Polymer; Sensors

Adsorption properties of magnetic CoFe2O4@SiO2 decorated with P4VP applied to bisphenol A

In this study, the preparation and adsorption properties of cobalt ferrite core-shell nanoparticles coated with silica and decorated with poly(4-vinylpyridine) (CoFe2O4@SiO2-P4VP) applied to bisphenol A (BPA) adsorption were described. The CoFe2O4-based core was coated by a nanometric layer of silica under Stöber conditions and followed by coating with poly(4-vinylpyridine) via surface polymerization in miniemulsion. The characterizations involved transmission electron microscopy (TEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR), thermogravimetry (TGA), dynamic light scattering (DLS) and zeta potential. The polymeric core-shell nanoparticle showed a spherical structure with a magnetic core of ca. 11 nm and a layer of silica of ca. 4 nm. The amount of poly(4-vinylpyridine) that decorated the nanoparticle surface was verified by thermogravimetric analysis. CoFe2O4@SiO2-P4VP exhibited the capacity to adsorb bisphenol A. The chemometric model indicated a significant effect between the ionic strength and pH of the solution in the adsorption of bisphenol A. CoFe2O4@SiO2-P4VP presented a superior adsorption capacity towards BPA (46.6 mg g−1) in optimized conditions. The adsorption kinetics of BPA by CoFe2O4@SiO2-P4VP involved a pseudo-second order process. Also, the adsorption isotherm indicated a multilayer process with data well-adjusted by Freundlich equation. The nanomaterial CoFe2O4@SiO2-P4VP can be reused in adsorption of BPA for up to eight cycles

Effect of high pressure and high temperature on the Na2O ⋅ 2CaO ⋅ 3SiO2 glass-ceramic’s structural properties

In this study, the Soda-lime-silicate system, with the Na2O⋅2CaO⋅3SiO2 (N1C2S3) composition, was used to study the effect of high pressure on structural properties of this glass-ceramic. Samples were produced and submitted to a single stage crystallization heat treatment at 720 ◦C for 30 min simultaneously in atmospheric pressure, 2.5 GPa, 4.0 GPa or 7.7 GPa. All characterizations were performed ex-situ. The major crystalline phase obtained is the Combeite, regardless of the pressure used, with indications of a β − CaSiO3 or Cristobalite-II phase transition happening due to the high pressure. Raman and Infrared spectroscopy showed that the phase transition could be a CaO precipitation on the material, due to the breaking of Si–O bonds and presence of Ca–O vibrational modes present on the high pressure samples. All results point to the Combeite crystalline phase being highly stable under pressures up to 7.7 GPa

Solution heat treatment of Ti-Nb alloys using a molten salt shield

Ti-Nb alloys have attracted growing attention for biomedical implant application due its low elastic modulus. Nb is a β-stabilizer in Ti alloys and retains its high biocompatibility. Thermal treatment plays a key role for optimization of mechanical properties and microstructure of Ti-Nb alloys. However, high oxygen affinity of Ti alloys requires the use of a protective atmosphere during their processing at high temperatures. In this context, we propose the use of molten salt as novel atmosphere protection during solution heat treatment of Ti-Nb alloys avoiding elaborated encapsulation. For that, Ti-Nb parts were solution treated in molten KCl followed by water quenching. Microstructure and phase transformation were evaluated by SEM, EDS, X-ray Diffraction, Elastic Modulus and Vickers microhardness measurements. No evidence of oxidation of Ti-Nb parts was found, which suggested that molten salt was an effective measure to protect Ti alloys from oxidation. After treatment, a martensitic microstructure was achieved. A martensitic structure enables to decrease elastic modulus to ca. 35 GPa, which can avoid stress shield in the case of bone implant application

Hybrid chitosan-coated manganese ferrite nanoparticles for electrochemical sensing of bifenox herbicide

A novel glassy carbon electrode (GCE) modified with hybrid chitosan-coated manganese ferrite nanoparticles (MnFe2O4@CTS) was applied for the electrochemical determination of bifenox, which is a nitrodiphenyl ether herbicide. The core-shell MnFe2O4@CTS nanoparticles were synthesized via ionic gelation and characterized by different techniques including transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, vibrating sample magnetometry, and thermogravimetric analysis. The modification of the GCE was performed by drop-casting method using MnFe2O4@CTS, previously dispersed by ultrasound. For the first time, the synthesized material was tested in the electroanalysis of environmental pollutants. The innovative modified MnFe2O4@CTS/GCE provided a significant increase of peak currents in the presence of bifenox. Electrochemical and interfacial characteristics of the electrodes were assessed by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimized conditions of square wave voltammetry and supporting electrolyte, it was possible to observe a linear dependence between the anodic peak current and the concentration of bifenox in the range from 0.3 to 4.4 μmol L−1. The limit of detection was estimated as 0.09 µmol L−1. The selectivity of the sensor was verified in the presence of other pesticides and the river water matrix; the interference response was found to be lower than 5%. The sensor showed excellent intra-day and inter-day repeatability presenting a relative standard deviation of 3.99% and 5.79%, respectively. Electrochemical determination of bifenox was performed in river and tap water samples. The recovery values were in the range of 82–97%. The novel analytical platform MnFe2O4@CTS/GCE presented promising features for application in environmental analysis of bifenox

Surface wettability of a natural rubber composite under stretching : a model to predict cell survival

We report the stress−strain effect of a stretchable natural rubber (NR)−calcium phosphate composite on the surface wettability (SW) using an innovative approach coupling a uniaxial tensile micromachine, goniometer, and microscope. In situ contact angle measurements in real time were performed during mechanical tension. Our results show that SW is guided by the stress−strain relationship with two different characteristics, depending on the static or dynamic experiments. The results evidenced the limits of the classical theory of wetting. Furthermore, based on the mechanically tunable SW of the system associated with the cytocompatibility of the NR composite, we have modeled such a system for application as a cell support. From the experimental surface energy value, our proposed 3D modeling numerical simulation predicted a window of opportunities for cell−NR survival under mechanical stimuli. The presented data and the thermodynamics-based theoretical approach enable not only accurate correlation of SW with mechanical properties of the NR composite but also provide huge potential for future cell supportability in view of tissue engineering

Abnormal resistive switching in electrodeposited Prussian White thin films

Prussian White (PW) layers were deposited on Au/Cr/Si substrates by electrodeposition and characterized by different techniques. Scanning electron microscopy (SEM) images and Raman mapping reveal a uniform and homogeneous deposit while scanning transmission electron microscopy (STEM) images disclose the grain boundary pattern and the thickness of 300 nm of the PW layer. Resistive switching (RS) effect with an ON/OFF ratio of about 102 was observed. The RS mechanism was investigated from the log-log current voltage plots. Ionic conduction was observed with an activation energy of 0.4 eV that could be associated with potassium ions as possible charge carriers at the grain boundaries. The endurance characteristics were investigated and a stable abnormal RS was observed for consecutive 500 cycles. Moreover, the retention was also evaluated and the high resistive state (HRS) and low resistive state (LRS) were stable up to 1000 s