Dielectric response, functionality and energy storage in epoxy nanocomposites: Barium titanate vs exfoliated graphite nanoplatelets

Patsidis, Anastasios C.; Kalaitzidou, Kyriaki; Psarras, G. C.

doi:10.1016/j.matchemphys.2012.05.060

Cited by 41 publications

(28 citation statements)

References 40 publications

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“…However, the conductivity is increased from 3.8 9 10 -10 to 1.5 9 10 -7 S/m [105]. The addition of GNP to epoxy gives a polymer-matrix composite exhibiting relative dielectric constant 16 at 1 MHz, whereas the addition of barium titanate to epoxy gives a composite exhibiting relative dielectric constant only 6.5 at 1 MHz [106].…”

Section: Graphite Nanoplatelet Compositesmentioning

confidence: 99%

A review of exfoliated graphite

2015

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Exfoliated graphite (EG) refers to graphite that has a degree of separation of a substantial portion of the carbon layers in the graphite. Graphite nanoplatelet (GNP) is commonly prepared by mechanical agitation of EG. The EG exhibits clinginess, due to its cellular structure, but GNP does not. The clinginess allows the formation of EG compacts and flexible graphite sheet without a binder. The exfoliation typically involves intercalation, followed by heating. Upon heating, the intercalate vaporizes and/or decomposes into smaller molecules, thus causing expansion and cell formation. The sliding of the carbon layers relative to one another enables the cell wall to stretch. The exfoliation process is accompanied by intercalate desorption, so that only a small portion of the intercalate remains after exfoliation. The most widely used intercalate is sulfuric acid. The higher concentration of residue in unwashed EG causes the relative dielectric constant (50 Hz) of the EG to be 360 (higher than 120 for KOH-activated GNP), compared to the value of 38 for the water-washed case. An EG compact is obtained by the compression of EG at a pressure lower than that used for the fabrication of flexible graphite. Compared to flexible graphite, EG compacts are mechanically weak, but they exhibit viscous character, outof-plane electrical/thermal conductivity and liquid permeability. The viscous character (flexural loss tangent up to 35 for the solid part of the compact) stems from the sliding of the carbon layers relative to one another, with the ease of the sliding enhanced by the exfoliation process.

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Section: Graphite Nanoplatelet Compositesmentioning

confidence: 99%

A review of exfoliated graphite

2015

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“…Interestingly, IP is observed in the neat epoxy spectrum, and loss index attains high values. IP has been detected in loss spectra of many polymers due to the presence of additives, impurities and plasticizers [32][33][34][35]. On the other hand, increased values of loss tangent should be related to high values of the dielectric loss ("&), since tan' is defined as the ratio of the imaginary to the real part of dielectric permittivity.…”

Section: Hydration Studiesmentioning

confidence: 99%

Barium ferrite/epoxy resin nanocomposite system: Fabrication, dielectric, magnetic and hydration studies

Kanapitsas¹,

Tsonos²,

Psarras³

et al. 2016

Express Polym. Lett.

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Abstract. Composite systems of epoxy resin and barium ferrite nanoparticles have been prepared, and studied varying the content of the inclusions. Morphology of prepared samples has been examined via scanning electron microscopy and X-ray diffraction spectra, while electrical and magnetic properties were investigated by means of broadband dielectric spectroscopy, and magnetization tests respectively. Finally, water vapor sorption measurements were conducted in order to study the water sorption dynamics of the system. Electron microscopy images revealed the successful fabrication of nanocomposites. Dielectric permittivity increases with filler content, while three relaxation processes were detected in the relative spectra. These processes are attributed to interfacial polarization, glass to rubber transition of the matrix, and re-orientation of polar side groups of the polymer's chain. Magnetization and magnetic saturation increase with magnetic nano-powder content. Nanocomposites absorb a small amount of water, not exceeding 1.7 wt%, regardless filler content, indicating their hydrophobic character.

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“…IP appears in heterogeneous systems because of the accumulation of non-bonded charges at the interface between the constituents of the system, where they form large dipoles. The inertia of these dipoles to follow the alternation of the applied field is the origin of the IP relaxation process [45][46][47][48][49], which is the slowest recorded effect. In general, IP is strengthened with the increase of the reinforcing phase and its relaxation time is enhanced.…”

Section: Mechanical Characterizationmentioning

confidence: 99%

Barium titanate/polyester resin nanocomposites: Development, structure-properties relationship and energy storage capability

Asimakopoulos¹,

Psarras²,

Zoumpoulakis³

2014

Express Polym. Lett.

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Abstract. Nanocomposite materials based on two different types of polyester matrix (a commercial type and a laboratory produced one) with embedded barium titanate nano-particles were developed and characterized. Structural and morphological characteristics of the produced composite specimens were studied via X-ray diffraction, Fourier transformation infra red spectroscopy, and scanning electron microscopy. Thermal, mechanical and electrical performance was examined via differential scanning calorimetry, bending and shear strength tests, and broadband dielectric spectroscopy, respectively. Mechanical strength appears to reduce with the increase of filler content. Commercial polyester's composites exhibit brittle behaviour, while laboratory polyester's composites exhibit an elastomeric performance. Dielectric data reveal the presence of four relaxation processes, which are attributed to motion of small parts of the polymer chain (!-mode), re-arrangement of polar side groups ("-mode), glass to rubber transition of the polymer matrix (#-mode) and Interfacial Polarization between the systems' constituents. Finally, the energy storing efficiency of the systems was examined by calculating the density of energy. Vol.8, No.9 (2014) 692-707 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2014.72 * Corresponding author, e-mail: G.C.Psarras@upatras.gr © BME-PT An outstanding position in the group of electroceramics is given to composite materials based on barium titanate. Barium titanate is a wide band gap semiconductive ferroelectric material with perovskite structure which has been of practical importance for over 60 years due to its specific electrical properties. Barium titanate's great significance is expressed in its applications, which include ceramic capacitors, PTCR thermistors (positive temperature coefficient resistors/thermistors or posistors), piezoelectric sensors, optoelectronic devices, transducers, actuators etc. [4][5][6][7][8][9][10]. Furthermore, it is being applied as a capacitive material in dynamic random access memories (DRAM) in integrated circuits. DRAM applications require both high dielectric constant and good insulating properties [10]. Semiconductor memories such as dynamic random access memories (DRAM's) and static random access memories (SRAM's) currently dominate the market. However, the disadvantage of these memories is that they are volatile, i.e. the stored information is lost when the power fails. The non-volatile memories available at this time include complementary metal oxide semiconductors (CMOS) with battery backup and electrically erasable read only memories (EEPROM's). These non-volatile memories are very expensive. The main advantages offered by ferroelectric random access memories (FRAM's) include non-volatility and radiation hardened compatibility with CMOS and GaAs circuitry, high speed (30ns cycle time for read/erase/rewrite) and high density (4 (µm) 2 /cell size) [11]. Up to now, the most important utility of BaTiO 3 / polymer composites is ...

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Dielectric response, functionality and energy storage in epoxy nanocomposites: Barium titanate vs exfoliated graphite nanoplatelets

Cited by 41 publications

References 40 publications

A review of exfoliated graphite

A review of exfoliated graphite

Barium ferrite/epoxy resin nanocomposite system: Fabrication, dielectric, magnetic and hydration studies

Barium titanate/polyester resin nanocomposites: Development, structure-properties relationship and energy storage capability

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