Dielectric properties of dielectrophoretically assembled particulate-polymer composites

Abstract

The dielectrophoretic effect is a phenomenon in which dipole-dipole interactions are induced between particles in a suspension by an electric field.1−5 This dipole interaction leads to the formation of chains or fibrils parallel to the applied electric field. Recently, the dielectrophoretic effect has been shown to be a possible composite assembly technique permitting property changes to be induced with the appropriate electric fields.6,7 The results presented in this paper show that the dielectrophoretic assembly process can be used to engineer anisotropy into composite materials. Various filler materials are aligned in a thermoset polyurethane matrix and the dielectric properties are measured. Comparisons are drawn between the dielectrophoretically assembled composites and those processed conventionally in the absence of an electric field. Dielectric properties are modeled with modified mixing laws and discussed in relation to the composite microstructure and the alpha relaxations of the polymer phase.

Dielectrophoretically structured piezoelectric composites with high aspect ratio piezoelectric particles inclusions

“…28,[31][32][33] It has also been demonstrated that alignment of high aspect ratio particles increases the permittivity of the composite. 8,34,35 The calculated values correspond well with the experimental values of composites with low aspect ratios but tend to fall short for composites with higher aspect ratios. This is possibly due to the contribution of the large aspect ratio fibers.…”

“…The series-parallel model for dielectric properties of structured piezoelectric composites, introduced by Bowen et al, 8 assumes perfectly intact chains of particles with equidistant spacing. This modification of the well known mixing rule for 1-3 composites includes a specific particle spacing parameter and has been adapted for piezoelectric properties of these materials.…”

“…The equations for permittivity, e DEP , and piezoelectric charge constant, d 33 DEP , according to this model 7,8 are presented in Eqs. (15) and (16):…”

“…The minimum inter particle distance due to roughness and irregular shape is significant compared to particle dimension in the field direction. 7,8 The R value can be increased by aligning particles with an aspect ratio (AR) higher than one. 8 The particle aspect ratio is defined as the longest axis over the shortest axis, AR ¼ c a .…”

“…7,8 The R value can be increased by aligning particles with an aspect ratio (AR) higher than one. 8 The particle aspect ratio is defined as the longest axis over the shortest axis, AR ¼ c a . However, it is also known that full alignment of large aspect ratio particles may be more difficult to achieve than it is for smaller aspect ratio particles when starting from a randomly oriented dispersion.…”