Free‐volume and crystallinity in low molecular weight poly(ethylene oxide)

Machado, Juliana Costa; Silva, Glaura G.; Oliveira, Fernando Castro de; Lavall, Rodrigo L.; Rieumont, Jacques; Licínio, Pedro; Windmöller, Dario

doi:10.1002/polb.21242

Cited by 29 publications

(16 citation statements)

References 45 publications

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“…The TPU presents the typical segmented structure, with T g 1 associated with a soft segments amorphous phase, and T g 2 and T m as the thermal events of the rigid segments arrangement [27]. The semicrystalline copolymer showed a low T g , probably related to the polyethylene glycol PPG block, and a low T m related to the polyethylene glycol block [28]. Variable results were obtained from the replicate analysis of electrolytes and composites.…”

Section: Resultsmentioning

confidence: 85%

Polymeric nanomaterials as electrolyte and electrodes in supercapacitors

et al. 2009

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The energy challenge requires a broad range of options for energy harvesting, storage, and conversion. We have produced polymeric coatings by spraying, to be used as electrolyte and electrodes in a fl exible electrochemical double layer capacitor. A thermoplastic polyurethane and a low molecular weight block copolyether were employed with LiClO 4 to prepare solid polymeric electrolytes. Carbon black (CB) and multi-walled carbon nanotubes (MWNTs) were dispersed in the polymer blend electrolyte to produce nanostructured composite electrodes. The conductivities increased with the addition of block copolyether and carbon nanotubes to the electrolyte and electrode, respectively. Scanning electron microscopy (SEM) and atomic force microscope (AFM) images of the nanocomposite electrodes showed nanoagglomerates of CB connected by carbon nanotubes. The solid supercapacitor prepared with these new materials as electrolyte and electrodes showed superior performance to other similar systems. The resulting safe and fl exible multilayer device can meet the requirements of modern devices. KEYWORDSPolymeric electrolyte blend, nanocomposite electrode, carbon black, carbon nanotube, supercapacitor Electrochemical capacitors or supercapacitors [1,2], using the electric double layer charge at the electrode/electrolyte interface of a highly porous electrode, can have an important role in new technologies. The properties of supercapacitors complement the defi ciencies of other power sources, such as batteries and fuel cells [3].Nanostructured carbon-based materials have been used in electrodes for electrochemical double layer capacitors (EDLC). The relationship between the surface area, total pore volume, average pore size, and the pore size distribution of the materials has a strong infl uence on the electrochemical characteristics of the resulting capacitor [3,4]. In such devices, activated carbons, carbon black or carbon nanotube composites have been employed as electrodes [3 6], mainly with liquid electrolytes [7]. Usually, the electrolytes employed in the electrochemical capacitors are acids, bases or salts dissolved in aqueous or organic solvents. Ionic liquids have also been investigated in supercapacitors [8 10]. The use of corrosive liquid electrolytes may cause dangerous leakages, which decrease the safety and lifetime of the capacitors [11,12]. To reduce problems associated Nano Research 734Nano Res (2009) 2: 733 739 with the management of corrosive ionic conductors, as well as to allow the preparation of thin film cells with high reliability, the use of solid polymer electrolytes (SPE) has been proposed [11, 13 16]. The performance of carbon-based polymer supercapacitors is closely associated with the characteristics of the materials used, such as new carbonaceous and electrolytes. The characteristics of the polymer electrolyte need to be tailored with the goal of increasing conductivity under specific experimental conditions. A degree of matching between the carbonaceous pore size and the microstructural arra...

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Section: Resultsmentioning

confidence: 85%

Polymeric nanomaterials as electrolyte and electrodes in supercapacitors

et al. 2009

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“…In addition, Misheva et al [2000] report that the free positron decay component I 2 increases linearly with crystallinity and find that its value correlates linearly to Vickers microhardness (VMH) values, thereby deducing that τ 2 and VMH are both determined by the crystalline regions in UHMW PEs. Machado et al [2007] reported wide-angle x-ray diffraction (WAXD), DSC, and PALS studies of six poly(ethylene oxide) samples, spanning the molecular weight range 1 to 10 kg/mol. They found that X c increased from about 70% to an asymptotic value of about 94% when molecular weight increased above 3 kg/mol.…”

Section: Pals As a Probe For Free Volume In Semicrystalline Polymersmentioning

confidence: 99%

“…(12.2), also decreased to an asymptotic value above M = 3 kg/mol. Machado et al [2007] also noted that I 3 ∼ 22%, even for the samples with highest crystallinity, and hence conclude that o-Ps forms and annihilates in the crystalline as well as amorphous regions of the polymer. The authors present no data on T g for their polymers, but T m increases with molecular weight and then levels off at M > 3 kg/mol, and hence it is interesting to note that the decrease observed in τ 3 with molecular weight is reminiscent of a similar effect observed in polystyrenes [Yu et al, 1994] and associated with the increasingly large contribution of holes associated with chain ends in lower-molecular-weight samples.…”

Section: Pals As a Probe For Free Volume In Semicrystalline Polymersmentioning

confidence: 99%

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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474 POSITRON ANNIHILATION LIFETIME STUDIES INTRODUCTIONThe theoretical and experimental background related to the positron annihilation lifetime spectroscopy (PALS) technique and its application as a quantitative probe for free volume in polymeric materials have been discussed extensively in Chapters 10 and 11, so we limit ourselves to a brief overview of these issues by way of introduction and commentary. Our principal focus here is to review what evidence has been generated using the PALS technique to provide insight into three topics of current interest, each of which involves probing specific heterogeneities in the amorphous polymeric phase. The first relates to the existence of concentration fluctuations in miscible polymer blends and their effect on materials properties, such as broadening of the glass transition region. The second concerns the fact that to interpret accurately the properties of certain semicrystalline polymers, such as gas transport, it is necessary to invoke a rigid amorphous phase, believed to involve the disordered chain segments that link crystalline lamellae, whose behavior differs from the usual (mobile) amorphous phase that exists far from the crystalline surface. The third topic involves evidence that a similarly rigid amorphous phase exists in polymeric nanocomposites, associated with polymer chains that lie near the surface of the inorganic particles. PALS AS A PROBE FOR FREE VOLUME IN POLYMERSA PALS experiment involves bringing a polymer sample into contact with a source of positrons, typically 22 Na. Energetic positrons emitted into the polymer by the source are slowed through collisions with atoms, creating an ionized radiation track (positron spur). In the last portion of the spur, referred to as the blob, the positron thermalizes, and either annihilates or finds a secondary electron created by the ionization to form a localized positronium atom Byakov, 2003, 2007;Stepanov et al., 2005a Stepanov et al., ,b, 2007. The spin 1 atom, called ortho-positronium (o-Ps), is three times more likely to form than is the spin 0 atom [para-positronium (p-Ps)] and is more stable than the latter, which annihilates within 125 ps. o-Ps has a long lifetime (140 ns in vacuum), which lifetime is determined by interactions with the medium. Typically, o-Ps annihilates via a pickoff mechanism, with the positron "picked off" by an electron of the medium that has opposite spin. Since o-Ps is easily polarizable, and therefore strongly repelled by the medium, it tends to localize in regions of low electron density (holes or free volume). The lifetime of o-Ps is then determined by the electron density and physical size of the hole in which it finds itself, and normally falls in the range of a few nanoseconds.Typically, therefore, a PALS spectrum consists of a minimum of three components: the short-lived p-Ps component with intensity I 1 and lifetime τ 1 = 125 ps; a free positron annihilation component, with intensity I 2 and lifetime τ 2 ; and the o-Ps component, with intensity I 3 and lifetime τ 3 . ...

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“…9 A espectroscopia de aniquilação de pósitrons (EAP) é uma ferramenta versátil na detecção e monitoramento da evolução de defeitos do tipo vacâncias em sistemas sólidos, 10 com presença cada vez mais marcante no estudo de materiais poliméricos. 11,12 Compósitos poliméricos com nanotubos de carbono foram alvo de estudos recentes utilizando as técnicas de EAP. 9,13 Dentre essas técnicas, a espectroscopia de vida média do pósitron (EVMP) permite monitorar as dimensões e concentração de volumes livres (vacâncias) através da obtenção de parâmetros de tempos de vida médios (t) e intensidades relativas (I) de formação de espécies positrônicas, respectivamente.…”

Section: Introductionunclassified

“…11,12 Esta técnica permite acessar como a distribuição de volume livre evolui com a temperatura, por exemplo.…”

Section: Introductionunclassified

Nanocompósitos de poliuretana termoplástica e nanotubos de carbono de paredes múltiplas para dissipação eletrostática

Lavall¹,

Sales²,

Borges³

et al. 2010

Quím. Nova

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Recebido em 9/3/09; aceito em 14/7/09; publicado na web em 27/11/09 THERMOPLASTIC POLYURETHANE AND MULTI-WALLED CARBON NANOTUBES NANOCOMPOSITES FOR ELECTROSTATIC DISSIPATION. Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 mm length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT.Keywords: thermoplastic polyurethane; carbon nanotube; nanocomposites. INTRODUÇÃOOs nanotubos de carbono (NTC) apresentam combinação única de propriedades mecânicas, elétricas e térmicas que os tornam excelentes candidatos para substituir ou complementar as cargas convencionais utilizadas no preparo de nanocompósitos poliméricos. Por exemplo, os nanotubos de carbono de parede única, denominados SWCNT da sigla em inglês, podem ser metálicos ou semicondutores, possuem módulo de Young entre 640 GPa-1TPa, resistência a tração de 150-180 GPa e condutividade térmica teórica de 6000 W/mK. Os MWCNT's (nanotubos de carbono de paredes múltiplas) possuem características elétricas entre metal e semicondutor, apresentam módulo de Young de 0,27-0,95 TPa, resistência à tração de 11-63 GPa e condutividade térmica entre 200-3000 W/mK (MWCNT isolados).1-3 Adicionalmente, os NTC possuem alta flexibilidade, baixa densidade mássica e alta razão comprimento/diâmetro (tipicamente entre 300-1000).A alta razão comprimento/diâmetro e o elevado número de interações de van der Waals entre os nanotubos de carbono levam à formação de agregados. O grande desafio no campo de nanocompósitos polímero/nanotubo de carbono é a dispersão dos nanotubos em tubos individuais (ou agregados de poucos tubos) nas matrizes poliméricas, 3,4 principalmente quando altas concentrações de nanotubos são empregadas.As poliuretanas (PU) são uma classe de materiais poliméricos com importância industrial significativa, por possuírem grande variedade de aplicações como espumas, adesivos, borrachas, entre outras. Uma PU típica é um polímero produzido por reação de poliadição de um isocianato (di ou polifuncional) com um poliol (polióis-poliéteres são os mais utilizados) e outros reagentes, principalmente agentes de cura ou extensores de cadeia. Na PU termoplástica (TPU), sem reticulação, os extensores de cadeia reagem com o di-isocianato para formar os segmentos rígidos. Os polióis dão origem aos segmentos flexíveis, que são geralmente incompatíveis com os segment...

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Free‐volume and crystallinity in low molecular weight poly(ethylene oxide)

Cited by 29 publications

References 45 publications

Polymeric nanomaterials as electrolyte and electrodes in supercapacitors

Polymeric nanomaterials as electrolyte and electrodes in supercapacitors

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

Nanocompósitos de poliuretana termoplástica e nanotubos de carbono de paredes múltiplas para dissipação eletrostática

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