Intrinsic tuning of poly (styrene-butadiene-styrene) (SBS) based self-healing dielectric elastomer actuators with enhanced electromechanical properties

The electromechanical properties of a thermoplastic styrene-butadiene-styrene (SBS) dielectric elastomer was intrinsically tuned by chemical grafting with polar organic groups. Methyl thioglycolate (MG) reacted with the butadiene block via a one-step thiol-ene ‘click’ reaction under UV at 25°C. The MG grafting ratio reached 98.5 mol% (with respect to the butadiene alkenes present) within 20 minutes and increased the relative permittivity to 11.4 at 103 Hz, with a low tan δ. The actuation strain of the MG grafted SBS dielectric elastomer actuator was ten times larger than the SBS-based actuator, and the actuation force was four times greater than SBS. The MG grafted SBS demonstrated an ability to achieve both mechanical and electrical self-healing. The electrical breakdown strength recovered to 15% of its original value, and the strength and elongation at break recovered by 25% and 21%, respectively, after three days. The self-healing behaviour was explained by the introduction of polar MG groups that reduce viscous loss and strain relaxation. The weak CH/π bonds through the partially charged (δ+) groups adjacent to the ester of MG and the δ- centre of styrene enable polymer chains to reunite and recover properties. Intrinsic tuning can therefore enhance the electromechanical properties of dielectric elastomers and provides new actuator materials with self-healing mechanical and dielectric properties

Intrinsic Tuning of Poly(styrene–butadiene–styrene)-Based Self-Healing Dielectric Elastomer Actuators with Enhanced Electromechanical Properties

The electromechanical properties of a thermoplastic styrene–butadiene–styrene (SBS) dielectric elastomer was intrinsically tuned by chemical grafting with polar organic groups. Methyl thioglycolate (MG) reacted with the butadiene block via a one-step thiol–ene “click” reaction under UV at 25 °C. The MG grafting ratio reached 98.5 mol % (with respect to the butadiene alkenes present) within 20 min and increased the relative permittivity to 11.4 at 103 Hz, with a low tan δ. The actuation strain of the MG-grafted SBS dielectric elastomer actuator was 10 times larger than the SBS-based actuator, and the actuation force was 4 times greater than SBS. The MG-grafted SBS demonstrated an ability to achieve both mechanical and electrical self-healing. The electrical breakdown strength recovered to 15% of its original value, and the strength and elongation at break recovered by 25 and 21%, respectively, after 3 days. The self-healing behavior was explained by the introduction of polar MG groups that reduce viscous loss and strain relaxation. The weak CH/π bonds through the partially charged (δ+) groups adjacent to the ester of MG and the δ- center of styrene enable polymer chains to reunite and recover properties. Intrinsic tuning can therefore enhance the electromechanical properties of dielectric elastomers and provides new actuator materials with self-healing mechanical and dielectric properties.<br/

Intrinsic Tuning of Poly(styrene–butadiene–styrene)-Based Self-Healing Dielectric Elastomer Actuators with Enhanced Electromechanical Properties

The electromechanical properties of a thermoplastic styrene–butadiene–styrene (SBS) dielectric elastomer was intrinsically tuned by chemical grafting with polar organic groups. Methyl thioglycolate (MG) reacted with the butadiene block via a one-step thiol–ene “click” reaction under UV at 25 °C. The MG grafting ratio reached 98.5 mol % (with respect to the butadiene alkenes present) within 20 min and increased the relative permittivity to 11.4 at 103 Hz, with a low tan δ. The actuation strain of the MG-grafted SBS dielectric elastomer actuator was 10 times larger than the SBS-based actuator, and the actuation force was 4 times greater than SBS. The MG-grafted SBS demonstrated an ability to achieve both mechanical and electrical self-healing. The electrical breakdown strength recovered to 15% of its original value, and the strength and elongation at break recovered by 25 and 21%, respectively, after 3 days. The self-healing behavior was explained by the introduction of polar MG groups that reduce viscous loss and strain relaxation. The weak CH/π bonds through the partially charged (δ+) groups adjacent to the ester of MG and the δ- center of styrene enable polymer chains to reunite and recover properties. Intrinsic tuning can therefore enhance the electromechanical properties of dielectric elastomers and provides new actuator materials with self-healing mechanical and dielectric properties.<br/

Vibration suppression using piezoelectric actuator-based active flexure joints for high precision operations

Flexure couplings are alternatives to conventional mechanical joints, eliminating tribological effects and joint reversal uncertainties. However, their low stiffness-induced dynamic errors hinder utilisation in high precision applications. Additionally, during operation flexure couplings can experience large deflections, leading to significant changes in their dynamic behaviour. An effective vibration control approach to minimise these effects is yet to be thoroughly investigated. To reduce resonance during operation, this work proposes to embed Micro-Fibre-Composites onto a passive flexure coupling structure, creating an active flexure coupling. A comparison between the mathematical model and measured system behaviour of passive and active flexure couplings shows the flexure coupling modification has insignificant impact on its elastic characteristics. Therefore, the robust mathematical representation of a system containing a passive flexure coupling is valid for designing feedforward motion control of an active flexure coupling. However, the performance of the active flexure coupling in vibration suppression is significant and demonstrated in both fixed poses and continuous motion-tracking of a two-link actuated system. This includes large deflections of the flexure coupling with a variation of the tip angle from −34.5 ∘ to 37.2 ∘. By implementing active flexure couplings into automated systems, high precision and high-value applications can be achieved.</p

Effects of off-plane deformation and biased bi-axial pre-strains on a planar contractile dielectric elastomer actuator

Dielectric elastomers are in a special class of electro-active polymers known for generating expansion in plane and contraction in thickness under voltage application. This paper advances the understanding of a planar contractile dielectric elastomer actuator (cDEA) that is distinct from conventional multi-layer cDEAs but generates comparable contractile strains. Its structure has a rod-constrained rhombus-shaped electrode region, which undergoes simultaneous in-plane contraction and extension during actuation depending on the configuration of the rod-constraining. It is demonstrated that when the planar cDEA is driven by high voltages, off-plane deformation (i.e., wrinkling) in the direction of contraction causes the rod-constrained electrode region to lose tension and extend in the lateral direction, resulting in a significant increase in contraction strain. It also demonstrates that the contraction strain can be increased further by having biased bi-axial pre-strains. By incorporating both effects, the new cDEA generates a maximum contraction strain of 13%, twice that reported previously for planar cDEAs. A modified planar cDEA, having an additional rigid frame to maintain the pre-strain in the lateral direction to contraction was also developed to demonstrate contractile force actuation. Finally, a stability study shows that the planar cDEA has a primary failure mode of electrical breakdown close to the corners of the rod-constrained electrode region. Having inactive regions around the active cell is essential for generating contraction and eliminating buckling of the planar cDEA in the lateral direction

Closed loop control of force operation in a novel self-sensing dielectric elastomer actuator

Closed loop feedback is essential in achieving the precise control of dielectric elastomer actuators (DEAs) due to their inherent nonlinear viscoelasticity. A novel self-sensing mechanism that uses capacitive sensing to detect the actuation of force in a dielectric elastomer sensing actuator (DESA) is proposed in this paper. In contrast to a conventional self-sensing DEA, it consists of an electro-active region (AR) for the actuation together with an independent electro-sensing region (SR). By doing so, the self-sensing mechanism does not exhibit longterm drift in the correlation between the structural deformation and the capacitive change, which is commonly found in conventional self-sensing DEAs. The results show that the proportional-integral (PI) controlled DESA performs effectively under uniaxial actuation. The DESA can suppress the relaxation of the viscoelastic DE and thus enable a constant force output. It also shows that the sensing capacity of the DESA can be enhanced further with appropriate electrode arrangement and motion-constraining. Furthermore, the results show that the DESA senses the off-plane expansion distinctly compared with the in-plane deformation, which helps to detect any wrinkling of the structure