All-organic dielectric-percolative three-component composite materials with high electromechanical response

Abstract

By combining the high-dielectric copper phthalocyanine oligomer ͑PolyCuPc͒ and conductive polyanline ͑PANI͒ within polyurethane ͑PU͒ matrix an all-organic three-component dielectric-percolative composite with high dielectric constant is demonstrated. In this three-component composite system, the high-dielectric-constant PolyCuPc particulates enhance the dielectric constant of the PU matrix and this combined two-component dielectric matrix in turn serves as the high-dielectric-constant host for the PANI to realize percolative phenomenon and further enhance the dielectric response. As a result, an electromechanical strain of 9.3% and elastic energy density of 0. Electroactive polymers ͑EAPs͒ are capable of converting energy in the form of electric charge and voltage to mechanical force and movement and vice versa. In recent years, several electroactive polymer actuator materials, whose responses are controlled by external electric fields, have generated considerable interest.1-4 However, one severe drawback of these EAPs is the very high operation electric field ͑Ͼ100 V/m͒ required to generate a high strain with elastic energy density much higher than those in the current available piezoelectric materials ͑elastic energy density Ͼ0.1 J/cm 3 ). 5,6 As has been pointed out in earlier publications, 7,8 one fundamental cause for such high fields is the low dielectric constant of these EAPs. From the energy conservation, the elastic energy density generated in an electroactive polymer cannot exceed the input electric energy density, which is K⑀ 0 E 2 /2 for a linear dielectric, where K is the dielectric constant, ⑀ 0 ϭ8.85ϫ10 Ϫ12 F/m, and E is the applied field. This simple fact points out the importance of raising the dielectric constant of the EAPs to achieve high electromechanical response with low applied fields.Recently high dielectric and electromechanical responses have been demonstrated in two-component composite actuator materials.7-9 Especially, a two-component percolative composite, fabricated by a combination of conductive polymer particulates ͓polyaniline ͑PANI͔͒ within the relaxor ferroelectric polymer matrix, raises the dielectric constant ͑Ͼ1000͒ substantially higher than the polymer matrix ͑ϳ50͒. 8,10,11 In composites of conductive fillers embedded in an insulation matrix, the variation of the dielectric constant of the composite with the concentration f of the conductive filler has been predicted to follow a critical behavior, 12,13

Colossal dielectric and electromechanical responses in self-assembled polymeric nanocomposites

“…25 In addition, giant dielectric constant values were observed and correlated to the formation of gain boundary barrier layers and interfacial polarization and percolation effects. 16,26 Our nanocomposite films have a complex microstructure and mobile charge carriers in the decorated o-CuPc which could result in an enhanced dielectric response caused by the Maxwell-Wagner space charge as reflected by the strong frequency dispersion of the dielectric responses. 27,28 What is unique is that, although the self-assembled nanocomposite exhibits such a high dielectric response, the net volume fraction of o-CuPc is about 3.5% in the nanocomposite.…”

“…[9][10][11] It is known that phthalocyanine as well as its oligomer has a strong tendency to form stack assemblies and microaggregates due to its planar shape and aromatic nature, [12][13][14] so it is hard for polymer dielectric matrix to directly disstack these high dielectric constant microaggregates due to the very weak interactions between them. 9,15,16 Hence, the preparation of the nanometer-scale building blocks, highly dispersed nanoparticles is necessary before selfassembly. Herein, we demonstrate a polymeric nanocomposite in which high dielectric constant o-CuPc nanoparticles were incorporated into the block polyurethane ͑PU͒ by the combination of "top-down" and "bottom-up" self-assembly approaches.…”

“…23 A similar phenomenon was also observed in several multiphase composites. 16 The high dielectric constant nanocomposite also leads to high electromechanical response. The field-induced strain was measured at different applied fields at room temperature and under an ac field of 1 Hz.…”

Front Matter: Volume 8340

“…Microparticles, nanoparticles and nanoclays are used to increase the dielectrical permittivity of the networks. Similar investigations have been performed by others [24][25][26] , however here we have put the emphasis on the combination of the filler to increase the dielectric strength and on maintaining a hight flexible network. The presence of fillers causes modifications to both dielectric and mechanical properties of the elastomers.…”

Multiscale instabilities in soft heterogeneous dielectric elastomers

“…The reason for this is the poor electromechanical coupling in typical polymers which have a limited ratio of dielectric to elastic modulus. An approach to challenge the issue is to consider heterogeneous DEs by combining an elastomer with a high dielectric or even conductive material [13][14][15][16][17]. This approach has been shown to be promising in experiments [8,18].…”