2 research outputs found
New Details to Relaxation Dynamics of Dielectric Composite Materials Comprising Longitudinally Opened Carbon Nanotubes
The
difference between intact and longitudinally opened multiwalled
carbon nanotubes (referred to as CNT and OCNT) has been studied in
their application as conductive filler in polymer composite materials.
The dielectric properties have been studied in a broad frequency range
at the temperatures varying from 293 K through 373 K. Introduction
of as little as 0.5% and 1.0% of the conductive filler dramatically
increased both parts of the complex permittivity. The percolation
threshold is registered at ∼1.5% filling fraction. The main
frequency dispersion of the dielectric permittivity lies in the low
frequency end of the tested spectrum: from 10<sup>2</sup> Hz through
10<sup>4</sup> Hz. At equal filling fractions, the permittivity of
the OCNT-based samples exceeds that of the intact CNT-based samples.
The relaxation dynamics is largely affected by the nanoscale geometry
of the filler: the temperature dependence of such parameters as dielectric
strength, activation energy, and relaxation time demonstrated significant
difference between the charge transfer mechanism in the CNT-based
and OCNT-based samples. The obtained activation energy is 150 and
85 kJ/mol for materials comprising CNTs and OCNTs, respectively. The
relaxation mechanism is complex, and the exact factors behind the
macroscopic dielectric properties of the tested materials cannot be
singled out with certainty. Several experimental data points suggest
that the individual nanotubes, not their aggregates, play the major
role in the observed electrical properties of the composites. At the
low loading fractions, we attained the highest dielectric strength
values among all the data reported by the present day for the CNT/polymer
host systems
Gas-Transport and the Dielectric Properties of Metathesis Polymer from the Ester of exo-5-Norbornenecarboxylic Acid and 1,1′-Bi-2-naphthol
Polymers from norbornenes are of interest for applications in opto- and microelectronic (low dielectric materials, photoresists, OLEDs). Norbornenes with ester motifs are among the most readily available norbornene derivatives. However, little is known about dielectric properties and the gas-transport of polynorbornenes from such monomers. Herein, we synthesized a new metathesis polymer from exo-5-norbornenecarboxylic acid and 1,1′-bi-2-naphthol. The designed monomer was obtained via a two-step procedure in a good yield. This norbornene derivative with a rigid and a bulky binaphthyl group was successfully polymerized over the 1st generation Grubbs catalyst, affording high-molecular-weight products (Mw ≤ 1.5·106) in yields of 94–98%. The polymer is amorphous and glassy (Tg = 161 °C), and it shows good thermal stability. Unlike most, polyNBi is a classic low-permeable glassy polymer. The selectivity of polyNBi was higher than that of polyNB. Being less permeable than polyNB, polyNBi unexpectedly showed a lower value of dielectric permittivity (2.7 for polyNBi vs. 5.0 for polyNB). Therefore, the molecular design of polynorbornenes has great potential to obtain polymers with desired properties in a wide range of required characteristics. Further tuning of the gas separation efficiency can be achieved by attaching an appropriate substituent to the ester and aryl group