Development of poly(dimethylsiloxane)-titania nanocomposites with controlled dielectric properties: Effect of heat treatment of titania on electrical properties

Dielectric and Ultrasonic Properties of PDMS/TiO2 Nanocomposites

This work presents the dielectric and ultrasonic properties of polydimethylsiloxane (PDMS) nanocomposites filled with titanium dioxide nanoparticles. The dielectric study was performed over a very broad range of frequencies (20 Hz-3 THz). The dielectric permittivity was almost frequency-independent in all the composites at room temperature over the whole range of measurement frequencies, and the dielectric losses were very low under these conditions (less than 2). The dielectric permittivity strongly increases with the nanoparticle concentration according to the Maxwell-Garnet model. Therefore, the investigated composites are suitable for various flexible electronic applications, particularly in the microwave and terahertz frequency ranges. Dielectric dispersion and increased attenuation of ultrasonic waves were observed at lower temperatures (below 280 K) due to the relaxation of polymer molecules at the PDMS/TiO2 interface and in the polymer matrix. The relaxation time followed the Vogel-Vulcher law, while the freezing temperature increased with the titanium dioxide concentration due to interactions between the polymer molecules and nanoparticles. The significant hysteresis in the ultrasonic properties indicated that titanium dioxide acts as a crystallization center. This is confirmed by the correlation between the hysteresis in the ultrasonic properties and the structure of the composites. The small difference in the activation energy values obtained from the ultrasonic and dielectric investigations is related to the fact that the dielectric dispersion is slightly broader than the Debye-type dielectric dispersion.

Dielectric and Mechanical Properties of PDMS-La2Ba2XZn2Ti3O14 (X = Mg/Ca/Sr) Nanocomposites

Flexible polydimethylsiloxane-La2Ba2XZn2Ti3O14 (X = Mg/Ca/Sr) [PDMS-LBT] nanocomposites with high permittivity (dielectric constant, k) are prepared through a room-temperature mixing process. The LBT nanoparticles used in this study are prepared through a high-temperature solid-state reaction. It is observed that LBT (X = Mg/Ca) nanoparticles are spherical in nature, with particle size ∼20 nm, as observed from the HRTEM images, whereas LBT (X = Sr) nanoparticles are cubical in nature with particle size ≥100 nm. These LBT (X = Mg/Ca/Sr) nanoparticles are crystalline in nature, as apparent from the XRD analysis and SAED patterns. The permittivity of LBT nanoparticles is higher when "Ca" is present in place of "X". These three oxides show a temperature-dependent dielectric behavior, where LBT nanoparticles with "Sr" show a sharp change in permittivity at a temperature of ∼105 °C. These kinds of oxide materials, especially LBT (X = Sr) nanoparticles/oxides, can be used in dielectric/resistive switching devices. The effect of LBT nanoparticle concentration on the dielectric and mechanical properties of PDMS-LBT nanocomposites is widely studied and found that there is a significant increase in dielectric constant with an increase in the concentration of LBT nanoparticles. There is a decrease in the volume resistivity with the increase in the LBT nanoparticle concentration. All the PDMS-LBT nanocomposites have low dielectric loss (ε″) compared to the dielectric constant value. It is found that both permittivity (ε') and AC conductivity (σac) of PDMS-LBT composites are increased with the temperature at a frequency of 1 Hz. The % elongation at break (% EB) and tensile strength (TS) decrease with the LBT nanoparticle concentration in the matrix PDMS, which is due to the non-reinforcing behavior of LBT nanoparticles. The distribution and dispersion of LBT nanoparticles in the matrix PDMS are observed through HRTEM and AFM/SPM.

Effect of carbons' structure and type on AC electrical properties of polymer composites: predicting the percolation threshold of permittivity through different models

The AC electrical properties of EVA- and NBR-based composites filled with different conductive fillers were investigated. Result shows several magnitudes of increment in AC electrical conductivity and dielectric permittivity after the addition of these conductive fillers, indicating that these materials can be used as supercapacitors. The magnitude of increment was varied according to polymer and filler types. Herein, we also have tested the applicability of different sigmoidal models to find out the percolation threshold value of permittivity for these binary polymer composite systems. It is observed that except sigmoidal-Boltzmann and sigmoidal-dose-response models, other sigmoidal models exhibit different values of percolation threshold when considered for any particular polymer composite system. The paper discusses the variation in results of percolation threshold with an emphasis on the advantages, disadvantages and limitations of these models. We also have applied the classical percolation theory to predict the percolation threshold of permittivity and compared with all the reported sigmoidal models. To judge the unanimous acceptability of these models, they tested vis-à-vis the permittivity results of various polymer composites reported in published literature. To comprehend, all the models except the sigmoidal-logistic-1 model were successfully applicable for predicting the percolation threshold of permittivity for polymer composites.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00396-023-05120-2.

High Performance of Titanium Dioxide Reinforced Acrylonitrile Butadiene Rubber Composites

Recently, dielectric elastomer actuators (DEA) have emerged as one of the most promising materials for use in soft robots. However, DEA needs a high operating voltage and high mechanical properties. By increasing the dielectric constant of elastomeric materials, it is possible to decrease the operating voltage required. Thus, elastomeric composites with a high dielectric constant and strong mechanical properties are of interest. The aim of this research was to investigate the effect of titanium dioxide (TiO₂) content ranging from 0 to 110 phr on the cure characteristics, and physical, dielectric, dynamic mechanical, and morphological properties of acrylonitrile butadiene rubber (NBR) composites. The addition of TiO₂ reduced the scorch time (t_s1) as well as the optimum cure time (t_c90) but increased the cure rate index (CRI), minimum torque (M_L), maximum torque (M_H), and delta torque (M_H - M_L). The optimal TiO₂ content for maximum tensile strength and elongation at break was 90 phr. Tensile strength and elongation at break were increased by 144.8% and 40.1%, respectively, over pure NBR. A significant mechanical property improvement was observed for TiO₂-filled composites due to the good dispersion of TiO₂ in the NBR matrix, which was confirmed by scanning electron microscopy (SEM). Moreover, incorporating TiO₂ filler gave a higher storage modulus, a shift in glass transition temperature (T_g) to a higher temperature, and reduced damping in dynamic mechanical thermal analysis (DMTA). The addition of TiO₂ to NBR rubber increased the dielectric constant of the resultant composites in the tested frequency range from 10² to 10⁵ Hz. As a result, TiO₂-filled NBR composite has a high potential for dielectric elastomer actuator applications.

Effect of aluminum nitride concentration on different physical properties of low density polyethylene based nanocomposites

In this study, blends of low-density polyethylene (LDPE)/aluminum nitride (AlN) ceramic nanocomposites have been prepared through melt blending technique. Increased loading of AIN leads to reduction in tensile properties but improvement in rheological property (storage modulus). The rheological behavior tends to become unique at higher frequencies (≥10 rad/s). Differential scanning calorimetry (DSC) results show that the total crystallinity has decreased with the increase in AlN loading in the composites. It is seen that there is an improvement in electrical conductivity, dielectric constant, and flammability properties with the addition of AlN in the nanocomposites. The experimental data of tensile modulus, electrical conductivity, and dielectric constant have been fitted with some available theoretical models to check the models’ applicability for the present composite systems. Results show that only Nicolais-Nicodemo model, McCullough model, and Rahaman-Khastgir model are applicable for predicting the tensile modulus, electrical conductivity, and dielectric constant of the composites, respectively.

Filler's impact on structure and physical properties in polyester resin–oxide nanocomposites

Impact of nanosized oxide particles of titania (titanium dioxide, rutile) and silica–titania fumed compound on structure relaxation processes in nanocomposites of an orthophtalic unsaturated styrene cross-linked polyester resin has been experimentally studied using the thermal desorption mass spectroscopy, the dielectric spectroscopy, and the positron annihilation lifetime spectroscopy. All the nanocomposites showed unmonotonous variations in the thermal resistance, the dielectric permittivity and losses, and the annihilation rates for both positrons and ortho-positronium atoms with increasing filler’s loading. The nanoparticle-loading effects can be explained on the assumption that the oxide particles embedded into a cross-linked polyester resin induce rearrangements in its structure. Several mechanisms of particle–polymer interface interaction compete simultaneously and thus promote the alterations in molecular structure of the nanocomposites. The mechanisms may include both chemical and electrostatic fastening of polyester chains and styrene cross-links to the active surface sites, the destruction of the styrene cross-links, and redistribution of electron density in polymers. The features of the loading effects observed in the different nanocomposites can be ascribed to distinctions in both of active surface sites and intrinsic dielectric properties of the filling oxide particles.