904 resultados para COPOLYMER MELTS
Resumo:
Back-scattered imaging, X-ray element mapping and electron microprobe analyzer (EMPA) chemical dating reveal complex compositional and age zoning in monazite crystals from different layers and textural positions in a garnet-bearing migmatite in SE Brazil. Y-rich (variable Y(2)O(3), averaging 2.5 wt.%) relict cores are preserved in mesosome and melanosome monazite, and correspond to 793 +/- 6 Ma inherited crystals possibly generated in a previous metamorphic event. These cores are overgrown and widely replaced by two generations of monazite, which are present in all migmatite layers. The first, also Y-rich (average 2.5 wt.% Y(2)O(3)), was produced at similar to 635 Ma during prograde metamorphism under subsolidus conditions, while the second has an Y-poor (<1.5 wt.% Y(2)O(3)), low Th/U signature, and precipitated from low Y and HREE anatectic melts produced by reactions in which garnet was inert. Quartz-rich trondhjemitic leucosome represents lower temperature melt (bearing some subsolidus quartz and garnet with included monazite) formed at temperatures below muscovite breakdown; its Y-poor monazite indicates an age of 617 +/- 6 Ma. Granitic leucosomes formed close to peak metamorphic conditions (T>750 degrees C) above muscovite breakdown have their slightly younger character confirmed by a 609 +/- 7 Ma low-Y monazite age. A similar 606 +/- 5 Ma age was obtained for low-Y monazite rims and domains in mesosome and melanosome, and reflects the time of monazite saturation in interstitial granitic melt that was trapped in these layers. Our results confirm that inherited monazite crystals can be preserved during partial melting at temperatures above muscovite breakdown. Moreover, careful textural control aided by X-ray chemical mapping may allow monazite generated at different stages in a similar to 25 Myr prograde metamorphic path to be identified and dated using an electron microprobe. (C) 2008 Elsevier B.V. All rights reserved.
Resumo:
Trace element and isotopic data obtained for mantle spinel Iherzolites and diorite dykes from the Baldissero massif (Ivrea-Verbano Zone, Western Italy) provide new, valuable constraints on the petrologic and geodynamic evolution of the Southern Alps in Paleozoic to Mesozoic times. Whole rock and mineral chemistry indicates that Baldissero Iherzolites can be regarded as refractory mantle residues following limited melt extraction. In particular, the Light Rare Earth Elements (LREE)-depleted and fractionated compositions of whole rock and clinopyroxene closely match modelling results for refractory residues after low degrees (similar to 4-5%) of near-fractional melting of depleted mantle, possibly under garnet-facies conditions. Following this, the peridotite sequence experienced subsolidus re-equilibration at lithospheric spinel-facies conditions and intrusion of several generations of dykes. However, Iherzolites far from dykes show very modest metasomatic changes, as evidenced by the crystallisation of accessory titanian pargasite and the occurrence of very slight enrichments in highly incompatible trace elements (e.g. Nb). The Re-Os data for Iherzolites far from the dykes yield a 376 Ma (Upper Devonian) model age that is considered to record a partial melting event related to the Variscan orogenic cycle s.l. Dioritic dykes cutting the mantle sequence have whole rock, clinopyroxene and plagioclase characterised by high radiogenic Nd and low radiogenic Sr, which point to a depleted to slightly enriched mantle source. Whole rock and mafic phases of diorites have high Mg# values that positively correlate with the incompatible trace element concentrations. The peridotite at the dyke contact is enriched in orthopyroxene, iron and incompatible trace elements with respect to the Iherzolites far from dykes. Numerical simulations indicate that the geochemical characteristics of the diorites can be explained by flow of a hydrous, silica-saturated melt accompanied by reaction with the ambient peridotite and fractional crystallisation. The composition of the more primitive melts calculated in equilibrium with the diorite minerals show tholeiitic to transitional affinity. Internal Sm-Nd, three-point isochrons obtained for two dykes suggest an Upper Triassic-Lower Jurassic emplacement age (from 204 31 to 198 29 Ma). Mesozoic igneous events are unknown in the southern Ivrea-Verbano Zone (IVZ), but the intrusion of hydrous melts, mostly silica-saturated, have been well documented in the Finero region, i.e. the northernmost part of IVZ and Triassic magmatism with calc-alkaline to shoshonitic affinity is abundant throughout the Central-Eastern Alps. The geochemical and chronological features of the Baldissero diorites shed new light on the geodynamic evolution of the Southern Alps before the opening of the Jurassic Tethys. (C) 2010 Elsevier B.V. All rights reserved.
Resumo:
Felsic microgranular enclaves with structures indicating that they interacted in a plastic state with their chemically similar host granite are abundant in the Maua Pluton, SE Brazil. Larger plagioclase xenocrysts are in textural disequilibrium with the enclave groundmass and show complex zoning patterns with partially resorbed An-rich cores (locally with patchy textures) surrounded by more sodic rims. In situ laser ablation-(multi-collector) inductively coupled plasma mass spectrometry trace element and Sr isotopic analyses performed on the plagioclase xenocrysts indicate open-system crystallization; however, no evidence of derivation from more primitive basic melts is observed. The An-rich cores have more radiogenic initial Sr isotopic ratios that decrease towards the outermost part of the rims, which are in isotopic equilibrium with the matrix plagioclase. These profiles may have been produced by either (1) diffusional re-equilibration after rim crystallization from the enclave-forming magma, as indicated by relatively short calculated residence times, or (2) episodic contamination with a decrease of the contaminant ratio proportional to the extent to which the country rocks were isolated by the crystallization front. Profiles of trace elements with high diffusion coefficients would require unrealistically long residence times, and can be modeled in terms of fractional crystallization. A combination of trace element and Sr isotope data suggests that the felsic microgranular enclaves from the Maua Pluton are the products of interaction between end-member magmas that had similar compositions, thus recording `self-mixing` events.
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The 590-580 Ma Itu Granite Province (IGP) is a roughly linear belt of post-orogenic granite plutons similar to 60 km wide extending for some 350 km along the southern edge of the Apia-Guaxupe Terrane in southeastern Brazil. Typical components are subalkaline A-type granites (some with rapakivi texture) that crystallized at varied, but mostly strongly oxidizing conditions, and contrast with a coeval association of also oxidized high-K calc-alkaline granites in terms of major (e. g., lower Ca/Fe) and trace elements (higher Nb, Y, Zr). Mantle-derived magmas (such as those forming the LILE-rich Piracaia Monzodiorite, with epsilon(Nd(t)) = -7 to -10, (87)Sr/(86)Sr((t)) = 0.7045-0.7055) are inferred to derive from enriched subcontinental lithosphere modified during previous subduction, and may have played a role in the generation of the A-type granites, adding melts or fluids or both to the lower crust from which the latter were generated. The IGP is interpreted as a reflection of crust uplift and increased heat flux during ascent of hot, less dense asthenosphere after continental collision, probably reflecting breakoff of an oceanic slab coeval to the right-lateral accretion of a terrane related to the Mantiqueira Orogenic System.
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The Amazonian Craton comprises an Archean domain surrounded by four successively younger Proterozoic tectonic provinces. Within the Rio-Negro-Juruena province the Serra da Providencia Intrusive Suite (1.60 and 1.53 Ga) consists of A-type rapakivi granites, charnockites and mangerites genetically associated with diabase dikes, gabbros and amphibolites lites. The original mafic melts were derived from a depleted mantle source (epsilon(Nd(T)) + 2.5 to +2.8; epsilon(Sr(T)) - 12.1). Underplated mafic magma induced melting of a short-lived fielsic crust, thus originating coeval felsic-inafic magmatism in a continental intraplate setting. The Colorado Complex, assigned to the Rondonian-San Ignacio province, comprises 1.35-1.36 Ga intrusive bimodal magmatism represented by monzonite gneisses associated with amphibolite, gabbro and metadiabase dikes intercalated with metasediments with detrital zircon that yield U-Pb ages of 1.35 to 1.42 Ga. Mafic samples display juvenile signatures (epsilon(Nd(T)) 0.0 to +5.2; epsilon(Sr(T)) -5.0 to -30.7) and are less contaminated than the Serra da Previdencia and Nova Brasiladndia ones. The generation of the basaltic magma is related to the subduction of an oceanic slab below the peridotite wedge (intraoceanic arc setting). Fluids and/or small melts from the slab impregnated the mantle. The Nova Brasilandia Sequence (Sunsas-Aguapei province) comprises a metasedimentary sequence intruded by 1.10-1.02 Ga metadiabases, gabbros, meta-gabbros, and amphibolites associated with granitic plutons (bimodal magmatism). The original tholeiitic magmas, derived from a depleted source (epsilon(Nd(T)) = +3.1 to +5.0), in a proto-oceanic setting, underwent subsequent contamination by the host rocks, as indicated by the isotopic and trace element data.
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A new aliphatic block copolyester was synthesized in bulk from transesterification techniques between poly((R)-3-hydroxybutyrate) (PHB) and poly(isosorbide succinate) (PIS). Additionally, other two block copolyesters were synthesized in bulk either from transesterification reactions involving PHB and poly(l-lactide) (PLLA) or from ring-opening copolymerization of l-lactide and hydroxyl-terminated PHB, as result of a previous transesterification reactions with isosorbide. Two-component blends of PHB and PIS or PLLA were also prepared as comparative systems. SEC, MALDI-TOF mass spectrometry (MALDI-TOFMS), (1)H and (13)C NMR spectroscopy, WAXD, solubility tests, and TG thermal analysis were used for characterization. The block copolymer structures of the products were evidenced by MALDI-TOFMS, (13)C NMR, and WAXD data. The block copolymers and the corresponding binary blends presented different solubility properties, as revealed by solubility tests. Although the incorporation of PIS sequences into PHB main backbone did not enhance the thermal stability of the product, it reduced its crystallinity, which could be advantageous for faster biodegradation rate. These products, composed of PHB and PIS or PLLA sequences, are an interesting alternative in biomedical applications.
Resumo:
In this paper we describe the electrosynthesis of poly[(2-bromo-5-hexyloxy- 1,4-phenylenevinylene)-co-(1,4-phenylenevinylene)] (BHPPV-co-PPV), a novel conducting copolymer, and its application as active layer of a chemiresistive gas sensor suitable for quantification of ethanol present in ethanol-gasoline mixtures normally present in the fuel tanks of flex-fuel vehicles. This information is crucial for the smooth operation of the engine since it permits optimal air:fuel ratio regulation. The sensor consists of an interdigitated electrode coated with a thin polymer film doped with dodecylbenzenesulfonic acid. On exposure to fuel vapours at room temperature, the device presents a linear correlation between its electrical conductance and the ethanol concentration in the fuel. (C) 2008 Elsevier B.V. All rights reserved.
Resumo:
This work presents a FT-Raman study (lambda(0) = 1064 nm) of naturally occurring polyester poly[(R)-3-hydroxybutyrate] (PHB) and its copolymer poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) with 5,8 and 12 mol % of HV (hydroxyvalerate). The FT-Raman spectra of films indicate that full width at half height of the band centered at 1725 cm(-1) and relative intensity of bands at 1443 and 1458 cm(-1) can be use to estimate the crystalline degree in film samples. The similarity between Raman spectra of molten PHB and PHBV and theirs CDCl(3) solutions suggested that molten polymers present similar conformation than polymers in solution. Raman data of these samples showed that bands at 1220, 1402, 1725, 2998 and 3009 cm(-1) are due to crystalline helical structure and the bands at 1453, 1740, 2881, 2938 and 2990 cm(-1) are originated from disordered domains. It is shown that composition of PHBV samples can be estimated by analyzing the ratio of the intensity of the bands at 2938 cm(-1) (nu C-H) and 1740 cm(-1) (nu C=O) in the spectra of solutions and of bands at 1354 (wCH(2)) and 1740 cm(-1) (nu C=O) in spectra of molten polymers. (C) 2010 Elsevier B.V. All rights reserved.
Resumo:
The excited-state dynamics of two polyfluorene copolymers, one fully conjugated containing phenylene vinylene units alternated with 9,9`-dihexylfluorenyl groups and the other segmented by -(CH2)(8)- spacer, were studied in dilute solution of different solvents using a picosecond single-photon timing technique. The excited-state dynamics of the segmented copolymer follows the Forster resonant energy-transfer model which describes intrachain energy-transfer kinetics among random oriented chromophores. Energy transfer is confirmed by analysis of fluorescence anisotropy relaxation with the measurement of a short decay component of about 60 ps. The fluorescence decay surface of the fully conjugated copolymer is biexponential with decay times of about 470 and 900 ps, ascribed to deactivation of chain moieties containing trans and cis isomers already in a photostationary condition. Thus, energy transfer is very fast due to the conjugated nature and rigid-rod-like structure of this copolymer chain.
Resumo:
This work presents a cyclic voltammetry study of the polyaniline/polyluminol copolymer on platinum electrodes. The results show that under determined conditions it is possible to obtain the copolymer deposited on a metallic surface. The luminol presence clearly affects the oxidation of aniline in the nucleation process and, additionally, changes the cyclic voltammetric characteristics of the obtained material. In this aspect, the copolymer presents hybrid characteristics when compared to the polyaniline and polyluminol separately obtained and seems to present intermediary conductivity.
Resumo:
Different compositions of visible-light-curable triethylene glycol dimethacrylate/bisglycidyl methacrylate copolymers used in dental resin formulations were prepared through copolymerization photoinitiated by a camphorquinone/ethyl 4-dimethylaminobenzoate system irradiated with an Ultrablue IS light-emitting diode. The obtained copolymers were evaluated with differential scanning calorimetry. From the data for the heat of polymerization, before and after light exposure, obtained from exothermic differential scanning calorimetry curves, the light polymerization efficiency or degree of conversion of double bonds was calculated. The glass-transition temperature also was determined before and after photopolymerization. After the photopolymerization, the glass-transi-tion temperature was not well defined because of the breadth of the transition region associated with the properties of the photocured dimethacrylate. The glass-transition temperature after photopolymerization was determined experimentally and compared with the values determined with the Fox equation. In all mixtures, the experimental value was lower than the calculated value. Scanning electron microscopy was used to analyze the morphological differences in the prepared copolymer structures. (C) 2007 Wiley Periodicals, Inc.
Resumo:
This technical note describes a detailed study on wax printing, a simple and inexpensive method for fabricating microfluidic devices in paper using a commercially available printer and hot plate. The printer prints patterns of solid wax on the surface of the paper, and the hot plate melts the wax so that it penetrates the full thickness of the paper. This process creates complete hydrophobic barriers in paper that define hydrophilic channels, fluid reservoirs, and reaction zones. The design of each device was based on a simple equation that accounts for the spreading of molten wax in paper.
Copolimeros de propileno-etileno com baixos teores de etileno : estrutura, morfologia e propriedades
Resumo:
A estrutura básica predomínante encontrada em todos os copolímeros foi a de longos blocos de polipropileno cristalizáveis, separados por unidades isoladas de etileno, que atuaram como defeitos cristalínos, reduzindo o grau de cristalínidade, além da perfeição e da espessura dos cristais. O gradual aumento do teor de etileno nas amostras origínais, até aproximadamente5 moI % provocou redução progressiva no comprimento dos blocos de propileno em ambas as frações cristalizável e elastomérica. Acima daquela concentração, o etileno mostrou por principal efeito a elevação do teor de borracha de etileno-propileno(EPR), refletíndo-seem pronunciado aumento da resistência ao impacto dos copolímeros, com pouca alteração do comprimento das seqüências propiJênicas nas frações cristaJizáveJe elastomérica. A estrutura e a morfologia da borracha EPR gerada foram analisadas, observando-se sua excepcional dispersão na fase contínua cristalína. Análise das curvas de fusão por DSC, utilizando-se conceitos cínéticos, demonstrou a existência de uma energia de ativação aparente de fusão, associada à introdução de unidades etilênicas nas cadeias, e relacionada ao processo de fusão dos cristais poliméricos. A redução de cristalínidade das amostras e o aumento de mobilidade de cadeia da fase amorfa para teores crescentes de etileno resultaram em redução da rigidez dos copolímeros. Propriedades ópticas, como "haze" e brilho mostraram-se dependentesdo balanço entre o teor de cristais e o teor de borracha. Um balanço global das propriedades analisadas sugere uma composição ótima para aplicações típicas de copolímeros de propileno-etileno aquela com teores de etileno entre 4 e 6 moI % (aproximadamente 3 -4 % em massa).
Resumo:
Foram estudadas, neste trabalho, interacões por complexos de transferência de carga, através de medidas gravimétricas do grau de inchamento de géis de poli(isopreno) reticulado,contendo grupos aceptores de carga, em presença de grupos doadores de carga, de pequeno peso molecular, dissolvidos em tolueno. Para este fim, poli(isopreno) sintético proveniente da COPERBO - Companhia Pernambucana de Borracha Sintética, após purificação em clorofórmio, foi caracterizado por espectroscopia no infra-vermelho. O seu peso molecular médio foi determinado por viscosimetria em tolueno e o valor de Mv obtido foi 8,25 x 105. Através de epoxidação da dupla ligacão e hidrólise ácida do respectivo anel oxirano, foram introduzidos no poli(isopreno), previamente purificado, grupos aceptores de carga do tipo cloranil e ácido 3,5-dinitro-benzóico, e grupos doadores de carga do tipo carbazola. Obteve-se, desta forma, copolímeros aceptores do tipo poli (isopreno - co-cloranil) e poli(isopreno-co-(3,5-dinitro-benzoato)) e copolímero doador do tipo poli(isopreno- co-carbazola). A quantidade de cada espécie introduzida foi determinada por espectroscopia no ultra violeta. Poli(isopreno) e os copolímeros contendo grupos doadores ou aceptores foram reticulados em solução utilizando 4,4'-(4,4'-difenilmetileno)-bis- 1,2,4-triazolina-3,5-diona (BPMTD). Os filmes reticulados, após retirada a fase sol, e secos à vácuo, foram submetidos a inchamento em tolueno puro e em solução de tolueno contendo grupos aceptores ou doadores de carga, nas proporções 10:1, 1:1 e 1:10 (polímero: grupo doador ou polímero: grupo aceptor de carga), a 25, 30, 35 e 40ºC. Das medidas gravimétricas do grau de inchamento, foi verificado a formação de complexos por transferência de carga entre os copolímeros aceptores e carbazola. Foi verificado ainda que copolímeros contendo grupos aceptores do tipo cloranil possuem maior tendência a formar complexos por transferência de carga do que copolímeros aceptores contendo grupos 3,5-dinitro-benzoíla.
Resumo:
Xenólitos ultramáficos, carregados até a superfície da Terra por magmatismo básico alcalino intraplaca, fornecem evidências diretas da natureza e processos envolvidos em modificações do manto litosférico subcontinental, como fusão parcial e metassomatismo. Estes xenólitos têm sido utilizados para identificar processos relacionados a evolução da litosfera continental, estimar a composição original do manto e a escala das heterogeneidades mantélicas. Raramente xenólitos ultramáficos mantélicos são encontrados em ambientes convergentes, no entanto na Patagônia (sul da América do Sul), diversas ocorrências são identificadas em basaltos alcalinos na região de arco e back arc da Cordilheira do Andes. Estes xenólitos oportunizam o estudo dos processos de interação entre a cunha mantélica, a placa oceânica subductada e a astenosfera. Nesta dissertação são apresentados dados petrográficos, mineralógicos, geoquímicos e de isótopos de Sr e O em 22 xenólitos ultramáficos de dois centros vulcânicos Mioceno-Holoceno distintos: Cerro del Mojon (41°06’S-70°13’W) e Estancia Alvarez (40°46’S-68°46’W), localizados na borda NW do Platô de Somuncura, norte de Patagônia (Argentina). A suíte de xenólitos ultramáficos do Cerro del Mojon consiste de espinélio dunitos e harzburgitos mantélicos anidros (Grupo1), espinélio lherzolitos mantélicos anidros (Grupo 2a) e hidratados (Grupo 2b) e espinélio clinopiroxenitos crustais (Grupo 3). Os xenólitos mantélicos do Grupo 1 são depletados (empobrecidos em ETR pesados e HFSE, com baixas razões 87Sr/86Sr em Cpx – 0,7028-0.7037), de alta PT (16-19 kbar, 950-1078 ºC), e têm evidências de metassomatismo críptico (enriquecimento em K, Na ETR leves) atribuído a componentes derivados de sedimentos da placa oceânica subductada, EM 2 (87Sr/86Sr em RT até 0,7126, 87Rb/86Sr até 1,66 e δ18O até +6.78‰). Estes valores anomalamente altos foram obtidos em amostras com bolsões de reação ao redor do espinélio, induzidos pela percolação de fluidos metassomáticos sob altas pressões seguida por descompressão (Sp+fluido→ Cpx+Ol+Sp+melt-andesítico-traquítico). Os xenólitos do Grupo 2 são moderadamente depletados (empobrecidos em HFSE, com baixas a altas razões 87Sr/86Sr em RT e Cpx – 0,7031-0,7045 e δ18O +5-6.2‰), de baixa PT (14-15 kbar, 936-942 ºC), e têm evidências de metassomatismo modal e críptico (enriquecimento em ETR leves, Na, K, Ti, Sr, Hf e anfibólio modal). O metassomatismo críptico parece estar relacionado ao mesmo agente metassomatizante do Grupo 1, mas ocorre em menor intensidade. O metassomatismo modal, no entanto, tem outra origem, podendo ser derivado de fontes mantélicas profundas. A quebra do anfibólio metassomático durante a descompressão e ascensão dos xenólitos até a superfície formou bolsões de reação ao redor do anfibólio (Anf→Cpx+Ol+Sp+melts-basálticos & andesíticos). A suíte de xenólitos ultramáficos de Estancia Alvarez consiste de espinélio harzburgitos anidros mantélicos (Grupo 1a) e espinélio dunitos anidros crustais (Grupo 1b), ambos com veios de serpentina. Os xenólitos mantélicos do Grupo 1a são depletados (empobrecidos em ETR leves e HFSE), de profundidades variadas (P entre 11-18 kbar) e de baixa T (877-961 ºC). Estes xenólitos têm enriquecimento em ETR leves, B, Rb e K, que pode estar relacionado a percolação de fluidos ricos em H2O e LILE gerados pela desidratação de filossilicatos dos sedimentos da placa oceânica (EM 2), como evidenciado por veios de serpentina e altas razões 87Sr/86Sr (0,7046-0,7298), 87Rb/86Sr (0,07-5,63) e valores de δ18O (até +7,88‰).