Šarūnas Svirskas

Dielectric Spectroscopy of Polymer Based PDMS Nanocomposites with ZnO Nanoparticles

Dielectric spectroscopy results of organic polymer Polydimethylsiloxane (PDMS) with different ZnO nanoparticle concentrations are presented in wide temperature range. Dielectric loss was measured as a function of electromagnetic field frequency at various temperatures. Our measurements have shown that the value and position of dielectric loss peak on a temperature scale depends on the concentration of ZnO nanoparticles within PDMS. The temperature behaviour of dielectric losses was compared with temperature dependencies of ultrasonic attenuation in the samples. It is shown that the maximum of dielectric losses in PDMS nanocomposite is described according to the Vogel-Fulcher law and the glass transition increases with ZnO concentration.

Ultrasonic and Dielectric Studies of Polyurea Elastomer Composites with Inorganic Nanoparticles

The temperature dependence of ultrasonic velocity and ultrasonic attenuation were measured in polyurea elastomer composites with inorganic nanoparticles. The decrease in the ultrasonic velocity along with an attenuation maximum was observed above the glass transition temperature, Tg. The shape and position of this peak are directly proportional to the amount of embedded nanoparticles. In addition, the sharp anomalies in the ultrasonic velocity and ultrasonic attenuation were observed above the glass transition temperature in semicrystalline polyurea elastomers. These anomalies are related to the corresponding first order phase transition of these crystalline domain-containing networks. The ultrasonic attenuation peak related to glass transition is considerably smaller in these polyurea networks showing a small influence of the soft domains below the melting temperature, Tm. The first order phase transition in the semicrystalline polyurea elastomers shows a large temperature hysteresis of more than 10 K, which was confirmed by dielectric investigations. The addition of small amounts of inorganic nanoparticles resulted in a shift of the first order phase transition temperature in semicrystalline nanocomposites.

Dynamics of Phase Transition in 0.4NBT-0.4ST-0.2PT Solid Solution

In this paper we present dielectric spectroscopy results of NBT-(0.6-x)ST-xPT with x = 0.2 solid solution. Dielectric investigations clearly showed a relaxor—normal ferroelectric phase transition at TPT = 419 K and low temperature and low frequency dispersion similar to coexistence of dipolar glass and ferroelectric phase. The mean relaxation time above the phase transition follows Vogel—Fulcher law with following parameters: E A = 0.179 eV, τ 0 = 3.39·10−14 s, T VF = 223 K.

Broadband dielectric spectroscopy of Pb-based relaxor ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with intermediate random fields

This work is devoted to the investigation of the broad band dielectric spectra of 0.83PbMg1/3Nb2/3O3-0.17PbTiO3 (PMN-17PT) single crystals which have intermediate random fields. The necessity to understand the impact of random fields for the phase transition in heterogeneous perovskite oxides is of central importance. The thorough studies of dielectric properties revealed that the structural phase transition in PMN-17PT has a very complex dynamics. The temperature dependences of dielectric permittivity show that this material has features characteristic of polar nano regions and order-disorder phase transition dynamics. We speculate that this is the fingerprint of the phase transition in such heterogeneous perovskite oxides.

Phase Transitions in Smectic Bent-Core Main-Chain Polymer Networks Detected by Dielectric and Ultrasonic Techniques

The dielectric and ultrasonic properties of a bent-core main-chain liquid-crystalline polymer network have been investigated. Dielectric measurements on this material showed two maxima in the real and imaginary components of the dielectric permittivity at 365 K and 450 K along with a temperature hysteresis showing the first order nature of the two phase transitions. Longitudinal ultrasonic attenuation and ultrasonic velocity measurements at 10 MHz frequency revealed some anomalies at the phase transition temperatures respect to the dielectric results. Above room temperature, a large ultrasonic attenuation was observed which can be related to the glass transition of this sample. Moreover, the piezoelectric sensitivity of this bent-core main-chain liquid-crystalline polymer network has also been studied.

Ultrasonic studies of polymer composites with inorganic nanotubes

The temperature dependencies of longitudinal ultrasonic attenuation and velocity in several groups of new polyurea elastomers and poly(ε-caprolactone) composites were measured. In region of the glass transition the large ultrasonic attenuation maxima were observed. These peaks have relaxation behavior and can be approximated by temperature dependant relaxation time described by Arrhenius equation. The position of ultrasonic attenuation maxima and activation energy of relaxation process depends on the structure of the polyurea network. The ultrasonic relaxation peak in poly(ε-caprolactone) is also related to glass transition. The influence of inorganic nanotubes and nanowires in polyurea elastomers and poly(ε-caprolactone) is also discussed.