Dielectric relaxation spectroscopy of amorphous and liquid‐crystalline side‐chain polycarbonates

Wübbenhorst, Michael; Koten, Ernout M. Van; Jansen, Johannes C.; Mijs, W. J.; Turnhout, J. van

doi:10.1002/marc.1997.030180211

Cited by 49 publications

(45 citation statements)

References 10 publications

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“…From t HN , the relaxation time at maximum loss, t max , is obtained analytically with Equation (2): For the localization of the processes that were covered by the strong conductivity contribution, we used, additionally to the complex dielectric function analysis, the first derivative method of e' to derive the e" as: e" calc = À(p/2)[@e'/@lnw], which provides a conduction-free dielectric loss peak. [26] …”

Section: Resultsmentioning

confidence: 97%

Conductivity of Poly(pyrrole)‐Poly(styrene sulfonate) Core–Shell Nanoparticles

2010

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The dielectric properties of poly(styrene) nanoparticles decorated at their surfaces with poly(styrene sulfonate) [PSS] brushes and subsequently loaded with polypyrrole (PPy) were studied. These film-forming materials which may serve as hole-injection layers in organic light-emitting diodes, exhibit a core-shell-type morphology with a core of electrically insulating poly(styrene) and a shell consisting of a corona of PSS chains which form the matrix in which the electrically conducting complex of PPy and PSS is embedded. This conducting complex exists in form of domains of nanoscale dimensions. Thin compressed pellets of these nanoparticles were studied using mainly impedance spectroscopy. Measurements were carried out in the temperature range between 123 and 453 K and frequency range from 10(-1) to 10(6) Hz. While earlier studies were centered around the effect of polypyrrole volume fraction on the conductivity films and pellets composed of these nanoparticles, the present study reveals in which way the conductivity can be modified by exchange of the mobile inorganic counter ions of PSS. Besides the free-acid form (H(+)), the Li(+)-, Na(+)- and Cs(+)-salts of PSS were investigated. The PPy volume fraction was the same for all PPy/PSS core-shell nanoparticles. The distance for phonon-assisted hopping between next-neighbor polypyrrolium chains is influenced by the presence of these inorganic cations. For all samples containing PPy, a transition from insulating to conducting behavior in the range of 300-350 K was found. Using the fluctuation-induced tunneling model, the average tunneling distance, as well as the potential energy barrier separating neighboring conducting grains was estimated. Finally, a detailed analysis of the dielectric spectra suggests the localization length of the charge carriers to be about 0.33 nm.

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Section: Resultsmentioning

confidence: 97%

Conductivity of Poly(pyrrole)‐Poly(styrene sulfonate) Core–Shell Nanoparticles

2010

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“…Both the Arrhenius-type thermal activation and the value for the activation energy E a $ 23 kJ/mol support an assignment of the c-process to local conformation transitions as known for polyethylene (c-process [21]) and many side-group polymers containing methylene spacers or tails [20,22]. Fitting of Eq.…”

Section: Dielectric Relaxationsmentioning

confidence: 96%

“…4 and 5, which show the dielectric loss e 00 deriv ðf ; T Þ for both materials as a function of the frequency and temperature. Like in previous studies [17,19,20], we have used the Ôconduction-freeÕ dielectric loss (e 00 deriv ), computated from the real part of the dielectric spectrum e 0 (f) [17], in order to eliminate excessive contributions from (Ohmic) conduction in the loss spectra. The resulting loss spectra reveal various relaxation processes as well as marked discontinuities indicating the first-order phase transitions.…”

Section: Dielectric Relaxationsmentioning

confidence: 99%

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Yildirim

Wübbenhorst

Mendes

et al. 2005

Journal of Non-Crystalline Solids

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The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Col h ) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C 10 Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C 10 Br, a Ôhigh temperatureÕ glass transition, manifested by a Vogel-Fulcher-Tammann (VFT) type a 2 -process, was found at À31°C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (a 1 ) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as À100°C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a ÔhinderedÕ polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails.

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“…The fourth, a*, process can be noticed only marginally in the dielectric loss E", because ohmic conduction dominates the dielectric loss at temperatures above the a process. In order to eliminate conduction from the dielectric loss curves, we have calculated the alternative loss E: from the permittivity E', which has proven to be successful in previous work [20,21], according to This yields a fair approximation of the 'conduction free' loss E" for broad relaxation peaks, while as a bonus for narrow Debye-like relaxation peaks, an additional sharpening is achieved [20]. The effectiveness of this procedure is illustrated for compound 1 in Figure 4.…”

Section: Relaxation Processes In Linear Self-assembling Polymersmentioning

confidence: 99%

Complex dynamics of hydrogen bonded self-assembling polymers

Wübbenhorst

Turnhout

Folmer

et al. 2001

IEEE Trans. Dielect. Electr. Insul.

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Supramolecular polymers, which are non-covalently bonded and formed by self association of di or trifunctional monomers exhibit, by virtue of quadruple hydrogen bonds, many of the properties of normal high molecular weight polymers, e.g. a dynamic rubber plateau. We focus on the molecular and cooperative dynamics of self-assembled linear polymers and networks, studied by broadband dielectric relaxation spectroscopy (DRS) in the frequency range from lop2 to lo6 Hz. The DRS analysis was backed up by dynamic mechanical and rheological experiments. In the high temperature region two loss processes (U and a*) show up, the relaxation times of which obey the Vogel-Fulcher-Tammann (VFT) law. The dielectric a process is related to the dynamic glass-rubber transition and is slightly faster than the corresponding mechanical a process. A slower (high-temperature) a* relaxation is identified as chemical, corresponding to the mean lifetime of the hydrogen bonded linkages in the supramolecular chains. Its relaxation time T~* was found to be 1 to 2 decades larger than the terminal flow relaxation time, indicating that the relaxation of an entire chain is dominated by the joint dynamics of many hydrogen bonds. The ,O relaxation, observed in both DRS and dynamic mechanical analysis (DMA) at temperatures below T,, arises from the local junction dynamics of hydrogen bonded units in the glassy state. Details of the temperature dependence and the shape of the loss peaks of the a and a* relaxations will be discussed in terms of temporary physical networks and cooperativity.

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Dielectric relaxation spectroscopy of amorphous and liquid‐crystalline side‐chain polycarbonates

Cited by 49 publications

References 10 publications

Conductivity of Poly(pyrrole)‐Poly(styrene sulfonate) Core–Shell Nanoparticles

Conductivity of Poly(pyrrole)‐Poly(styrene sulfonate) Core–Shell Nanoparticles

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Complex dynamics of hydrogen bonded self-assembling polymers

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