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| 2. |
- Barreto, C., et al.
(författare)
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Graphite nanoplatelet/pyromellitic dianhydride melt modified PPC composites: Preparation and characterization
- 2013
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 54:14, s. 3574-3585
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Tidskriftsartikel (refereegranskat)abstract
- The properties of composites prepared by melt compounding from graphite nanoplatelets (GNP) and pyromellitic anhydride modified poly(propylene carbonate) (PPC) were investigated. GNPs of different morphologies and acid residue levels were selected. Acid residues in GNP grades were detrimental for PPC in terms of thermal stability, stiffness and conservation of the molecular weight. The exfoliation of graphite nanoparticles was challenging, and morphologies of combined tactoids with thicknesses both on the micro and nano scales were observed. The filler contributed to the thermal stability, and the mechanical reinforcement was observed from approximately 6 wt% GNP and accompanied by an increase in the glass transition temperature. For a specific GNP grade, at a 15 wt% filler content, the glass transition temperature increased by 10 degrees C and the storage modulus measured at 20 and 30 degrees C increased correspondingly by a factor of ca. 3 and 30, respectively. Solid state NMR spin-spin relaxation time T-2 measurements (Carr-Purcell-Meiboom-Gill pulse sequence) revealed three significantly different components. Using PLS, empirical models were established which enable the prediction of some viscoelastic parameters as a function of filler parameters and the average T-2.
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| 3. |
- Barreto, C., et al.
(författare)
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Multiwall carbon nanotube/PPC composites: Preparation, structural analysis and thermal stability
- 2013
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Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 49:8, s. 2149-2161
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Tidskriftsartikel (refereegranskat)abstract
- The focus of this report concerns the preparation nanocomposites from poly(propylene carbonate) (PPC) and multiwall carbon nanotubes (MWNTs). A solvent route using tetrahydrofuran, ethoxylated non- ionic surfactants combined with sonication was found to be successful in deagglomerating and dispersing the nanotubes. Transmission electron microscopy revealed highly disentangled and dispersed nanotubes and was supported by the qualitative stability evaluations. The morphology and molecular mobility of the prepared nanocomposites (0.5, 3.0 and 5.0 wt% of nanotubes) were characterized by rheology, microscopy, low-field solid-state nuclear magnetic resonance, and electrical conductivity. The networking of nanotubes was highest with a stearyl alcohol ethoxylate surfactant, and was found to improve with the sonication time. Nanotube percolation was established, both rheologically and electrically, from a filler content of approximately 0.5 wt%. A higher tendency toward particle agglomeration was observed at higher MWNT loadings. Only minor changes in the glass transition temperature were measured presumably due to the presence of solvent and surfactant residues. The thermal stability was marginally improved by increasing the loading and dispersion of the nanotubes, and appeared to be modified by solvent and surfactant residues.
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| 5. |
- Grishina, A. D., et al.
(författare)
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Fast photorefractive polymer composites based on nanocrystalline J-aggregates of the
- 2004
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Ingår i: Synthetic Metals. - : Elsevier BV. - 0379-6779. ; 144:2, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- The hole and electron drift mobility, photoelectric properties as well as influence of temperature, dark current and also relative position of oxidation potentials of the interacting components on photorefractive characteristics of the composites from aromatic polyimide doped with nanocrystalline J-aggregates of a cyanine dye are presented. The nanocrystalline J-aggregates were used as the photosensitizers and also as nonlinear optical chromophores. The experimental electric field dependence of the charge carrier photogeneration efficiency is well fitted by Onsager equation when the quantum yield of the bound thermalized electron-hole pairs φ0=1 and the initial separation of the charges in the pair r0=14.1Å. The charge photogeneration time constant determines the response time of the photorefractive grating formation. The polymer composites exhibit gain coefficient Γ=218cm-1 and response time shorter than 20ms at applied electric field 50V/μm and a intensity of each writing beam 30mW/cm2. The net gain coefficient Γ-α=143cm -1.
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| 9. |
- Grishina, A. D., et al.
(författare)
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Photoelectric, nonlinear optical, and photorefractive properties of polyvinylcarbazole composites with graphene
- 2013
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Ingår i: High Energy Chemistry. - 0018-1439 .- 1608-3148. ; 47:2, s. 46-52
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Tidskriftsartikel (refereegranskat)abstract
- Polyvinylcarbazole (PVK) composites containing graphene in an amount of somewhat less than 0.15 wt % exhibit third-order dielectric susceptibility due to the presence of graphene, as well as photoelectric and photorefractive sensitivity at 1064 nm. The photorefractive (PR) effect is known to occur in a polymer composite that possesses both photoelectric sensitivity and nonlinear optical properties. The photoelectric, nonlinear optical, and PR properties of PVK composites with graphene have been considered in this paper.
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