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A stacked dielectric elastomer actuator (DEA) consists of multiple layers of elastomeric dielectrics interleaved with
compliant electrodes. It is capable of taking a tensile load if only the interleaving compliant electrodes provide a good
bonding and enough elasticity. However, the stacked configuration of DEA was found to produce less actuation strain as
compared to a single-layer configuration of pre-stretched membrane. It is believed the binder for compliant electrodes
has a significant influence on the actuation strain. Yet, there has yet systematic study on the effect of binder. In this
paper, we will study the effects of binder, solvent, and surface fictionalization on the compliant electrodes using the
conductive filler of Multi-Walled Carbon Nanotube (MWCNT).
Two types of binders are used, namely a soft silicone rubber (Mold Max 10T) and a soft silicone gel (Sylgard 527 gel).
The present experiments show that the actuators using binders in the compliant electrodes produce a much lower areal
strain as compared to the ones without binders in them. It is found that introducing a binder in the electrodes decreases
the conductivity. The MWCNT compliant electrode with binder remains conductive (<1TΩ) up to a strain of 300%,
whereas the one without binder remains conductive up to a strain of 800%. Changing the type of binder to a softer and
less-viscous one increases the percolation ratio for MWCNT-COOH filler from 5% to 15% but this does not
significantly increase the actuation strain.
In addition, this study investigates the effect of MWCNT functionalization on the dielectric elastomeric actuation. The
compliant electrodes using the MWCNT functionalized with (-COOH) group was also found to have a lower electrical
conductivity and areal actuation strain, in comparison to the ones using the pristine MWCNT filler. In addition to binder,
solvent for dispersing MWCNT-COOH was found to affect the actuation strain even though the solvent is eventually
removed by evaporation from the MWCNT-COOH electrode. The actuators with MWCNT-COOHs electrodes, prepared
from the solvent dispersion, produce a low actuation strain even though these electrodes have good conductivity and
these solvents do not degrade the physical properties of the dielectric layer. This finding on the solvent effect has yet
been clearly understood.
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