Página 1 dos resultados de 2312 itens digitais encontrados em 0.020 segundos

Surface characterization of absorbing polymer films deposited on transparent glasses

GONCALVES, Debora; TRAVAIN, Silmar A.; GIACOMETTI, Jose A.; IRENE, Eugene A.
Fonte: EUROPEAN POLYMER FEDERATION Publicador: EUROPEAN POLYMER FEDERATION
Tipo: Artigo de Revista Científica
ENG
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557.8742%
PANI films were deposited on glass substrates by in-situ polymerization and characterized by UV-VIS spectroscopy and atomic force microscopy. A method is developed to accurately analyze ellipsometric data obtained for transparent glass substrates before and after modification with absorbing polymer films. Surface modification was made with an overlayer such as polyaniline ( PANI), which exhibits different optical properties by varying its oxidation state. First, the issue of using transparent substrates for ellipsometry studies was examined and then, spectroscopic ellipsometry was used to characterize absorbing overlayers on transparent glasses. The same methodologies of data analysis can be also applied to other absorbing films on transparent substrates, and deposited by different techniques.

Controlling the luminescence properties of poly(p-phenylene vinylene) entrapped in Langmuir and Langmuir-Blodgett films of stearic acid

SAKAI, Andrei; WANG, Shu H.; PERES, Laura O.; CASELI, Luciano
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
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461.94402%
Properties of hybrid films can be enhanced if their molecular architecture is controlled. In this paper, poly (p-phenylene vinylene) was mixed with stearic acid in order to form stable hybrid Langmuir monolayers. Surface properties of these films were investigated with measurements of surface pressure, and also with polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The films were transferred from the air-water interface to solid supports through the Langmuir-Blodgett technique, and the viability of the film as optical device was investigated with fluorescence spectroscopy. Comparing the fluorescent spectra for the polymer in solution, as a casting film, and as an LB film, the emission bands for LB films were narrower and appeared at lower wavelengths. The interactions between the film components and the design for the LB film may take advantage of the method to immobilize luminescent polymers in mixed ultrathin films adsorbed in solid matrices. (C) 2011 Elsevier B.V. All rights reserved.; FAPESP; CNPq; INCT-INEO (Brazil)

Detection of microwaves using the organic semiconductor poly(p-phenylenevinylene)

MARLETTA, Alexandre; NOGUEIRA, Sandra L.; SILVA, R. A.; OLIVEIRA JUNIOR, Osvaldo Novais de
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
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461.94402%
We report a new procedure to convert the polymer precursor poly(xylylidene tetrahydrothiophenium chloride) (PTHT) into poly(p-phenylenevinylene) (PPV) using microwave irradiation. Spin-coated PTHT films were irradiated at room temperature under ambient conditions in a commercial microwave oven, with varying power from 20W to 100W. Complete conversion was reached within only 5 min of irradiation for powers above 50W, yielding PPV films with absorption and photoluminescence spectra that are practically indistinguishable from the spectra of thermally converted PPV films, which require ca. 2 h of a high temperature (similar to 200 degrees C) thermal treatment. In addition to a much faster conversion procedure, the irradiation with microwaves led to a red shift in the absorption spectrum of a PTHT film, which varied linearly with the time of irradiation. These films can then be used as low-cost, easy-to-use detectors of microwaves. (C) 2010 Elsevier B.V. All rights reserved.; Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG); FAPEMIG; Ministério da Ciência, Tecnologia e Inovação do Brasil (MCTI); IMMP/MCT; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq

On the energy transfer from a polymer host to the rhenium(I) complex in OLEDs

MIZOGUCHI, Sergio Kenji; PATROCINIO, Antonio Otavio Toledo; IHA, Neyde Yukie Murakami
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
565.1664%
Photoluminescence and electroluminescence of PVK films doped with fac-[ClRe(CO)(3)(bpy)], bpy=2,2`-bipyridine, are investigated. Photoluminescence spectra of spin-coated PVK films (lambda(exc)=290 nm) exhibit a broad band centered at 405 nm. As the concentration of dopant increases, the polymer emission is quenched and a band at 555 nm appears (isosbestic point at 475 nm). In OLEDs with ITO/PEDOT:PSS/PVK/butylPBD/Al architecture doped with fac-[ClRe(CO)(3)(bpy)], the polymer host emission is completely quenched even at the lowest concentration of dopant. The electroluminescence spectra of the devices show that there is an efficient energy transfer from the host to the dopant, which exhibits a very intense emission at 580 nm. (C) 2009 Elsevier B.V. All rights reserved.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES; FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); CNPq; Financiadora de Estudos e Projetos (FINEP); CNPq/CTEnerg

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether, lithium perchlorate, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

COSTA, Luciano T.; SIQUEIRA, Leonardo J. A.; NICOLAU, Bruno G.; RIBEIRO, Mauro C. C.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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460.0571%
Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) with LiClO(4), PEGdME/LiClO(4), and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, PEGdME/[bmim]PF(6), are compared. Raman spectroscopy suggests stronger interactions in PEGdME/LiClO(4) than PEGdmE/[bmim]PF(6), thus corroborating previous results obtained by molecular dynamics simulations. Quantum Chemistry methods have been used to calculate vibrational frequencies and the equilibrium structure of segments of the polymer chain around the cation. A consistent picture has been obtained from Raman spectroscopy, density functional theory (DFT) calculations, and molecular dynamics simulations for these polymer electrolytes. (C) 2010 Elsevier B.V. All rights reserved.

Synthesis and spectroscopic characterization of polymer and oligomers of ortho-phenylenediamine

SESTREM, Ricardo H.; FERREIRA, Daniela C.; LANDERS, Richard; TEMPERINI, Marcia L. A.; NASCIMENTO, Gustavo M. do
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
564.84258%
Poly(ortho-phenylenediamine) and oligomers of ortho-phenylenediamine were chemically synthesized and characterized by UV-vis, (1)H and (13)C NMR, FTIR and resonance Raman spectroscopies. Polymerization of ortho-phenylenediamine in HCl medium with ammonium persulfate only leads the trimer compound, in disagreement with some previous reports. Nevertheless, in acetic acid medium it was possible to prepare a polymer constituted by ladder phenazinic segments with different protonation levels and quinonediimine rings (polyaniline-like). X-ray absorption at N K-edge (N K XANES), X-ray photoelectron (XPS) and Electron paramagnetic resonance (EPR) spectroscopies were used to determine the different kinds of nitrogen presents in this class of polymer. N K XANES spectrum of poly(ortho-phenylenediamine) shows the band of -N=nitrogen of non-protonated phenazinic rings at 398.2 eV. In addition, XPS and N K XANES data confirm the presence of different types of protonated nitrogens in the polymeric poly(ortho-phenylenediamine) chain and the EPR spectrum shows that the polymer has a very weak polaronic signal. (C) 2009 Elsevier Ltd. All rights reserved.; FAPESP (Brazilian agency); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; National Synchrotron Light Laboratory (LNLS/Brazil); National Synchrotron Light Laboratory (LNLS/Brazil)[1026/01]; National Synchrotron Light Laboratory (LNLS/Brazil)[1427/02]; National Synchrotron Light Laboratory (LNLS/Brazil); National Synchrotron Light Laboratory (LNLS/Brazil); National Synchrotron Light Laboratory (LNLS/Brazil)[1432/02]; National Synchrotron Light Laboratory (LNLS/Brazil)[2169/03]; National Synchrotron Light Laboratory (LNLS/Brazil)

Electroluminescence of phenylene-vinylene random copolymers with different conjugation lengths

SCHULER, Tunisia Eufrausino; WANG, Shu Hui; ONMORI, Roberto Koji; SANTOS, Gerson; SANTOS, Emerson Roberto; BURINI JR., Elvo Calixto; ANDRADE, Adnei Melges de
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
465.1664%
PPV random derivates were synthesized and characterized. Polymer light emitting diodes (PLEDs) were assembled using the random copolymers as emissive layer and showed EL in the blue-green region in function of the method of preparation. The increase in the average conjugation degree in the polymer chain led to the reduction of the turn-on voltage of the device. The addition of Alq3 as ETL increased tenfold the luminescence efficiency. (C) 2009 Elsevier B.V. All rights reserved.

Nanostructures on spin-coated polymer films controlled by solvent composition and polymer molecular weight

Dario, Aline Ferrera; Macia, Henrique B.; Petri, Denise Freitas Siqueira
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
470.1178%
In this study we systematically investigated how the solvent composition used for polymer dissolution affects the porous structures of spin-coated polymers films. Cellulose acetate butyrate (CAB) and poly(methylmethacrylate) with low(PMMA-L) and high (PMMA-H) molecular weights were dissolved in mixtures of acetone (AC) and ethyl acetate (EA) at constant polymer concentration of 10 g/L The films were spin-coated at a relative air humidity of 55+/-5%, their thickness and index of refraction were determined by means of ellipsometry and their morphology was analyzed by atomic force microscopy. The dimensions and frequency of nanocavities on polymer films increased with the acetone content (phi(AC)) in the solvent mixture and decreased with increasing polymer molecular weight. Consequently, as the void content increased in the films, their apparent thicknesses increased and their indices of refraction decreased, creating low-cost anti-reflection surface. The void depth was larger for PMMA-L than for CAB. This effect was attributed to different activities of EA and AC in CAB or PMMA-L solution, the larger mobility of chains and the lower polarity of PMMA-L in comparison to CAB. (C) 2012 Elsevier B. V. All rights reserved.; Pro-Reitoria de Graduacao...

Photophysical properties of a fluorene-bipyridine copolymer and its complexes with europium

Turchetti, D. A.; Rodrigues, P. C.; Berlim, L. S.; Zanlorenzi, C.; Faria, G. C.; Atvars, T. D. Z.; Schreiner, W. H.; Akcelrud, L. C.
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
461.94402%
The synthesis and structural characterization of a europium complexed fluorene-bipyridine copolymer are described. A level of ion insertion of 80% in molar basis was achieved, and theoretical calculations showed that it required a twist of 179 degrees (49 kJ) between the pyridine units. Spectroscopy data showed that no electronic coupling between the main backbone and the complexation sites had occurred, but these hindered the interchain aggregation observed in the non complexed polymer. Preliminary electroluminescence studies showed that the EL and PL spectra are consistent, and that the ion had a trapping effect in the charge transport. (C) 2011 Elsevier B.V. All rights reserved.; INEO (National Institute for Organic Electronics); INEO (National Institute for Organic Electronics); CNPq (National Research Council); CNPq (National Research Council)

Novel polymer electrolytes based on gelatin and ionic liquids

Leones, Rita; Sentanin, F.; Rodrigues, Luisa C.; Ferreira, Rute A. S.; Marrucho, Isabel M.; Esperanca, Jose M. S. S.; Maule, Agnieszka Joanna Pawlicka; Carlos, Luis D.; Manuela Silva, M.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
462.6597%
This study describes the results of the characterization of polymer electrolytes using gelatin matrix doped with europium triflate and/or different ionic liquids. Samples of solvent-free electrolytes were prepared and characterized by ionic conductivity measurements, thermal analysis, electrochemical stability, X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. Electrolyte samples are thermally stable up to approximately 220 degrees C. All the materials synthesized are totally amorphous. The room temperature conductivity maximum of this electrolyte system is based on ionic liquid 1-ethyl-3-methylimidazolium acetate, (C(2)mim)(OAc) (1.18 x 10(-4) S cm(-1) at 30 degrees C). The electrochemical stability domain of all samples is about 2.0 V versus Li/Li+. This new series of materials represents a promising alternative in polymer electrolytes research field. The preliminary studies carried out with electrochromic devices (ECDs) incorporating optimized compositions have confirmed that these materials may perform as satisfactory multifunctional component layers in the field of "smart windows". This new materials, will open a land of promising applications in many areas: optics, energy, medicine for example as membranes and separation devices...

Using narrowband pulse-shaping to characterize polymer structure and dynamics : Deathstar GHz spectroscopy

Vachhani, Neal Arvind, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 122 leaves; 2950805 bytes; 2946460 bytes; application/pdf; application/pdf
EN_US
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(cont.) The validation of this technique for probing amorphous polymer structure and dynamics lays the ground for further study of heterogeneous materials, such as nanocomposites and block copolymers.; A narrowband pulse-shaper called the Deathstar has been used along with a picosecond acoustic technique to study amorphous polymers. The temperature dependence of the longitudinal acoustic velocity and the frequency dependence of the acoustic attenuation have been measured. The frequency range of longitudinal phonons studied is not directly accessible by other spectroscopies. Probing material response in this intermediate regime is valuable because it helps characterize secondary transitions and energy dissipation mechanisms in polymers. Broadband experiments have been done to study the temperature dependence of the acoustic velocity for polystyrene and poly(methyl methacrylate) from 10 K to 300 K. The results are in line with literature values and the predictions of a model based on acoustic impedance mismatch theory. Narrowband studies with the technique used were previously limited to amorphous silica. They are extended for the first time to amorphous polymers. The Deathstar GHz spectroscopy is used to determine the absolute acoustic attenuation coefficient as a function of frequency for PMMA. The values obtained are similar to those found in literature. However...

Synthesis and characterization of conducting polymer actuators

Vandesteeg, Nathan A. (Nathan Alan)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 126 leaves
ENG
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465.1664%
Conducting polymers are known to mechanically respond to electrochemical stimuli and have been utilized as linear actuators. To date, the most successful mechanism for actuation is ionic ingress and egress, though mechanisms based on conformational changes and molecular interactions have also been proposed. In the pursuit of new conducting polymer actuators it is necessary to design, synthesize, and characterize new materials, spanning scientific disciplines from synthetic chemistry to materials and mechanical engineering. As such, the topics of synthesis and characterization of new conducting polymers are discussed, highlighting developments in techniques and instrumentation. Actuation in poly(3,4-ethylenedioxythiophene), or PEDOT, and composites of PEDOT and carbon nanotubes is presented, demonstrating strains of 4.5% and strain rates of 0.2% per second with faster responses generated in carbon nanotube composites. Actuation in poly(3-hexylthiophene) is presented, demonstrating the observation of a novel actuation mechanism relating the potential of the polymer to the mechanical response. Further study of the actuation of polypyrrole at temperatures above 25°C is also discussed, in which response times decrease and magnitudes increase with temperature. Discrete time models of equivalent circuits and diffusion are utilized to predict conducting polymer actuator performance.; by Nathan A. Vandesteeg.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

Multiscale chemomechanics of polymer deformation under contact : predicting structure-property correlations from the bulk to the interphase

Tweedie, Catherine Anne
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 181 p.
ENG
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470.1178%
The development of nanoscale polymeric materials for mechanical applications necessitates advances in small-volume experimental techniques and analyses that reflect the viscoelastoplastic behavior of such materials. In this thesis, the time-dependence and response of homogeneous engineering polymers under confined contact loading are characterized as a function of polymer physical and structural properties. The validity of the time-independent metric indentation hardness Hi is evaluated through the combination of nanoindentation and atomic force microscopy imaging. In addition, the classic, time-dependent metric creep compliance J(t) is used to establish the experimental conditions necessary for linear elastic behavior for a set of thermoplastic and thermoset materials. For large indentations (hmax > 1 um), properties are tacitly assumed to reflect the properties of bulk polymer; however, this assumption does not hold within 100 nm of a free surface or interface of amorphous polymers such as polystyrene and polycarbonate. The contact deformation mechanism near an amorphous polymer surface is found to scale with the surface area of contact, suggesting the dynamic formation of a structural interphase region. Chemical probe functionalization experiments are developed to explore the effects of probe surface charge on the probe-polymer interface and contribute to the understanding of the interphase that dominates nanocomposite material response. A technique to rapidly screen mechanical response of combinatorial polymer libraries is presented...

A conjugated polymer plastic gel

Alcazar Jorba, Daniel
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 119 p.
ENG
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471.80062%
We present a gel route to process highly oriented conjugated polymer films and fibers. The incorporation of hexafluoroisopropanol, a strong and stable dipolar group, to the polythiophene backbone enhances the solubility and especially, the hydrogen bond forming capabilities of the polymer. This functionalization enables the polymer to build up an isotropic self-supporting network structure based on a combination of polymer-polymer chain interactions and interchain hydrogenbondings. These thermally reversible physical crosslinks incorporate plasticity in the conjugated polymer gel. The gel network can be melted and then transformed via mechanical deformation to form an anisotropic gel with the chains highly aligned along the tensile direction. The oriented gel morphology comprises a distribution of crystalline clusters in an overall swollen network. In these ordered regions, conjugated backbones are [pi]-stacked with respect to each other neighbors. The mechanically induced structural rearrangement from an isotropic to an anisotropic conjugated polymer gel occurs when transitioning from the molten state to the gel state. This study highlights the versatility of incorporating plasticity in the design of conjugated polymer materials via a gel processing technology and its potential for applications.; by Daniel Alcazar Jorba.; Includes bibliographical references (p. 107-119).; Thesis (M. Eng.)--Massachusetts Institute of Technology...

Mechanical behaviour analysis of polyester polymer mortars modified with recycled GFRP waste materials

Ribeiro, M. C. S.; Meixedo, João Paulo; Fiúza, António; Dinis, M. L.; Castro, Ana Cristina Meira; Silva, Francisco J. G.; Costa, C.; Ferreira, F.; Alvim, Mário Rui
Fonte: World Academy of Science, Engineering and Technology Publicador: World Academy of Science, Engineering and Technology
Tipo: Artigo de Revista Científica
Publicado em //2011 ENG
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461.63363%
In this study the effect of incorporation of recycled glass-fibre reinforced polymer (GFRP) waste materials, obtained by means of milling processes, on mechanical behaviour of polyester polymer mortars was assessed. For this purpose, different contents of recycled GFRP waste powder and fibres, with distinct size gradings, were incorporated into polyester based mortars as sand aggregates and filler replacements. Flexural and compressive loading capacities were evaluated and found better than unmodified polymer mortars. GFRP modified polyester based mortars also show a less brittle behaviour, with retention of some loading capacity after peak load. Obtained results highlight the high potential of recycled GFRP waste materials as efficient and sustainable reinforcement and admixture for polymer concrete and mortars composites, constituting an emergent waste management solution.

Apatite-polymer composites for the controlled delivery of bone morphogenetic proteins

Yong, Tseh-Hwan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 140 leaves; 9942234 bytes; 9948145 bytes; application/pdf; application/pdf
ENG
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471.80062%
Current treatment of bone defects due to trauma, cancer, or degenerative spine diseases involves the implantation of a bone graft. Autografts, which are harvested from the patient's own body, are associated with problems of limited availability and surgical morbidity. The use of allografts obtained from donors is also not desirable due to the risks of disease transmission and the costs of maintaining bone banks. The ideal solution would be to regenerate native bone to fill the defects. A group of potent growth factors known as bone morphogenetic proteins (BMPs) have been hailed as alternatives to bone grafts due to their ability to elicit new bone formation. Clinical use of BMPs involves loading the protein solution onto collagen sponges and subsequent implantation. However, these conventional collagen carriers show rapid clearance of BMPs within [approx.] 2 weeks, whereas bone healing is a longer process, especially in higher mammals. The poor BMP retention in collagen sponges may explain the greater response variability in higher mammals, ranging from full bone bridging within weeks to no bone union. These sponges are also not capable of tunable or multifactor release that could benefit healing in certain anatomic sites, e.g. avascular sites and prolonged non-unions. Hence...

Time-resolved spectroscopic characterization of ballistic impact events in polymer and nanocomposite materials

Saini, Gagan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 95 p.
ENG
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461.94402%
A detailed understanding of how materials respond to ballistic shock-loading is critical for the design and development of new protective materials. However, the nonlinear viscoelastic deformation present in polymers and nanocomposites during and immediately following a ballistic impact event is not currently well understood. The dynamic mechanical responses of materials experiencing ballistic shock-loading conditions are quite complex, with large amplitude compressions resulting in strain rates in excess of 106 s-1 and pressures exceeding several GPa. Historically, if one wants to study materials under ballistic shock loading conditions, a gas gun apparatus is necessary to generate appropriate high strain rate events. However, advances in high power ultra-fast laser amplifier systems have opened the possibility of optically generating ballistic shocks which are comparable to a shock wave generated by gas gun apparatus. Time-resolved mechanical property information, such as elastic modulus, bulk modulus, shear modulus, and Poisson's ratio are measured using impulsive stimulated thermal scattering, a laser-based photoacoustic technique.; (cont.) A series of polymeric and polymer based nanocomposite material systems are studied, including multilayered thin films of alternating layers of polymer and hard nanoparticles...

Energy absorption in Ni-Mn-Ga/ polymer composites

Feuchtwanger, Jorge
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 143 p.; 3538896 bytes; 3538683 bytes; application/pdf; application/pdf
ENG
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465.1664%
In recent years Ni-Mn-Ga has attracted considerable attention as a new kind of actuator material. Off-stoichiometric single crystals of Ni2MnGa can regularly exhibit 6% strain in tetragonal martensites and orthorhombic martensites have shown up to 10% strain when subjected to a magnetic field. These crystals are brittle and the production of single crystals can be quite costly. Terfenol-D, a commercially available giant-magnetostrictive material, suffers from some of the same drawbacks. It was found that composite materials made from Terfenol-D particles in a polymeric matrix could solve the issue of the brittleness while retaining a large fraction of the strain output of the alloy. At first glance a similar approach could be used to solve the brittleness issue of Ni-Mn-Ga, but the low blocking force of these alloys reduces the chances of achieving a Ni-Mn-Ga/polymer composite actuator. However, the stress-strain loops for Ni-Mn-Ga show a large mechanical hysteresis. This ability to dissipate energy makes this alloys very desirable for damping applications, and by putting particles of Ni-Mn-Ga in a composite, their brittleness becomes less of an issue.; (cont.) It is shown that by curing Ni-Mn-Ga/polymer composites under a magnetic field it is possible to align the particles in chains and to orient them so they will respond to a uniaxial load. The magnetic measurements show that there are twin boundaries in the particles that can be moved by an external stress. Stress-induced twin boundary motion in the particles is confirmed more directly by x-ray diffraction measurements...

Incorporating fluctuations and dynamics in self-consistent field theories for polymer blends

Mueller, Marcus; Schmid, Friederike
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/01/2005
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We review various methods to investigate the statics and the dynamics of collective composition fluctuations in dense polymer mixtures within fluctuating-field approaches. The central idea of fluctuating-field theories is to rewrite the partition function of the interacting multi-chain systems in terms of integrals over auxiliary, often complex, fields, which are introduced by means of appropriate Hubbard-Stratonovich transformations. Thermodynamic averages like the average composition and the structure factor can be expressed exactly as averages of these fields. We discuss different analytical and numerical approaches to studying such a theory: The self-consistent field approach solves the integrals over the fluctuating fields in saddle-point approximation. Generalized random phase approximations allow to incorporate Gaussian fluctuations around the saddle point. Field theoretical polymer simulations are used to study the statistical mechanics of the full system with Complex Langevin or Monte Carlo methods. Unfortunately, they are hampered by the presence of a sign problem. In dense system, the latter can be avoided without losing essential physics by invoking a saddle point approximation for the complex field that couples to the total density. This leads to the external potential theory. We investigate the conditions under which this approximation is accurate. Finally...

Engineering Polymer Informatics: Towards The Computer-Aided Design of Polymers

Adams, Nico; Murray-Rust, Peter
Fonte: Wiley-VCH Publicador: Wiley-VCH
Tipo: Artigo de Revista Científica
EN
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460.0571%
The computer-aided design of polymers is one of the holy grails of modern chemical informatics and of significant interest for a number of communities in polymer science. The paper outlines a vision for the in silico design of polymers and presents an information model for polymers based on modern semantic web technologies, thus laying the foundations for achieving the vision.