Influence of silane coupling agent on microstructure and properties of CCTO-P(VDF-CTFE)composites

Influence of the coupling agent on microstructure and dielectric properties of ceramic-polymer composites is systematically studied using CaCu_(3)Ti_(4)O_(12)(CCTO)as the filler,trichloro-(1H,1H,2H,2H-perfluorooctyl)-silane(Cl_(3)-silane)as coupling agent,and P(VDF-CTFE)88/12 mol.%copolymer as the matrix.It is demonstrated that Cl_(3)-silane molecules can be attached onto CCTO surface using a simple process.The experimental results show that coating CCTO with Cl_(3)-silane can improve the microstructure uniformity of the composites due to the good wettability between Cl_(3)-silane and P(VDF-CTFE),which also significantly improves the electric breakdown field of the composites.It is found that the composites using CCTO coated with 1.0 wt.%Cl_(3)-silane exhibit a higher dielectric constant with a higher electric breakdown field.For the composites with 15 vol.%CCTO that is coated with 1.0 wt.%Cl_(3)-silane,an electric breakdown field of more than 240 MV/m is obtained with an energy density of more than 4.5 J/cm^(3).It is also experimentally found that the dielectric constant can be used to easily identify the optimized content of coupling agent.

Characterization of percolation behavior in conductor-dielectric 0-3 composites

The equationε_(eff)■/φ_(c)φ)^(s)which shows the relationship between effective dielectric constant(ε_(eff))and the filler concentration(φ),is widely used to determine the percolation behavior and obtain parameters,such as percolation thresholdφc and the power constant s in conductor-dielectric composites(CDCs).Six different systems of CDCs were used to check the expression by fitting experimental results.It is found that the equation can fit the experimental results at any frequency.However,it is found that the fitting constants do not reflect the real percolation behavior of the composites.It is found that the dielectric constant is strongly dependent on the frequency,which is mainly due to the fact that the frequency dependence of the dielectric constant for the composites close toφ_(c)is almost independent of the matrix.

Dielectric response and percolation behavior of Ni–P(VDF–TrFE) nanocomposites

Conductor–dielectric 0–3 nanocomposites using spherical nickel nanoparticles as filler and poly(vinylidene fluoride–trifluoroethylene)70/30 mol.%as matrix are prepared using a newly developed process that combines a solution cast and a hotpressing method with a unique configuration and creates a uniform microstructure in the composites.The uniform microstructure results in a high percolation threshold’φc(>55 vol.%).The dielectric properties of the nanocomposites at different frequencies over a temperature range from -70℃ to 135℃ are studied.The results indicate that the composites exhibit a lower electrical conductivity than the polymer matrix.It is found that the nanocomposites can exhibit an ultra-high dielectric constant,more than 1500 with a loss of about 1.0 at 1 kHz,when the Ni content(53 vol.%)is close to percolation threshold.For the nanocomposites with 50 vol.%Ni particles,a dielectric constant more than 600 with a loss less than 0.2 is achieved.It is concluded that the loss including high loss is dominated by polarization process rather than the electrical conductivity.It is also found that the appearance of Ni particles has a strong influence on the crystallization process in the polymer matrix so that the polymer is converted from a typical ferroelectric to a relaxor ferroelectric.It is also demonstrated that the widely used relationship between the dielectric constant and the composition of the composites may not be valid.

Physical aspects of 0-3 dielectric composites

0-3 dielectric composites with high dielectric constants have received great interest for various technological applications.Great achievements have been made in the development of high performance of 0-3 composites,which can be classified into dielectric–dielectric(DDCs)and conductor–dielectric composites(CDCs).However,predicting the dielectric properties of a composite is still a challenging problem of both theoretical and practical importance.Here,the physical aspects of 0-3 dielectric composites are reviewed.The limitation of current understanding and new developments in the physics of dielectric properties for dielectric composites are discussed.It is indicated that the current models cannot explain well the physical aspects for the dielectric properties of 0-3 dielectric composites.For the CDCs,experimental results show that there is a need to find new equations/models to predict the percolative behavior incorporating more parameters to describe the behavior of these materials.For the DDCs,it is indicated that the dielectric loss of each constituent has to be considered,and that it plays a critical role in the determination of the dielectric response of these types of composites.The differences in the loss of the constituents can result in a higher dielectric constant than both of the constituents combined,which breaks the Wiener limits.