Work-per-cycle analysis for electromechanical actuators

The force generated by a polypyrrole actuator operating under isometric conditions has been shown to decrease as the initial load applied to the actuator increases. The origin of the decrease in force generated was found to be the change in modulus that occurs upon electrochemical stimulation of the polypyrrole. A simple analytical model is introduced to describe these effects. Efforts to increase the force generated from polypyrrole involved the preparation of various bundles formed from hollow PPy tubes. Isotonic strains of approximately 0.5% were obtained at an external force of 2000 mN (5 MPa), higher than all previous reports.

show abstract

“…Under these conditions, the blocking force (that opposing force needed to prevent any movement) is predicted to be [9] :…”

Section: Introductionmentioning

confidence: 99%

Force generation from polypyrrole actuators

Spinks¹,

Campbell²,

Wallace³

2005

Smart Mater. Struct.

View full text Add to dashboard Cite

show abstract

“…Young's modulus has been shown to significantly affect actuation strains 5 . Externally applied stress has also been shown to change the EWC of gels [2][3][4] and to shift the transition temperature of thermally induced discontinuous phase transitions [14][15][16][17] , such as the classical gel collapse that occurs in poly(N-isopropylacrylamide) at 33 • C. Practical actuator devices will always be subjected to external loads, so it is important to characterize their response under load.…”

mentioning

confidence: 99%

“…The modulus-induced contraction partially counteracts the natural expansion of the gel leading to lower net expansions when higher tensile stresses were applied. The effect of changing modulus on the pH-induced actuation can be calculated using models described elsewhere 5,6 and is illustrated schematically in Fig. 2a.…”

mentioning

confidence: 99%

Surprising shrinkage of expanding gels under an external load

et al. 2005

Self Cite

View full text Add to dashboard Cite

H ydrogels are fascinating and useful in that they can show large volume changes in response to various stimuli, such as temperature or chemical environment 1 . Here we report the peculiar observation that chemically crosslinked hydrogels that normally expand owing to a change in electrolyte pH can be made to shrink in certain circumstances. Specifically, these hydrogels contract when tested at a constant compressive force and subjected to a pH change that causes expansion in the absence of the applied load. When tested under tension, the gels always expand. Although the effects of external stress on the swelling of gels is known 2-4 , the concomitant change in gel mechanical properties during pH switching was found to be a more dominant effect in our studies. However, existing mechanical models 5,6 used to predict dimensional changes in actuator materials could not explain both the tensile and compression results. In addition, we show that the friction between metal plates of the apparatus and the gel is a key factor in explaining the contractile actuation under compressive loads. The observations reported in this paper are important for the successful design and use of hydrogel actuators in devices such as valves for microfluidics.Volume changes occur in polyelectrolyte hydrogels when the thermodynamic balance between expansion forces (electrostatic repulsion and osmotic pressure of counterions) and contractile forces (stretching of elastically active network chains) is shifted by changes in the chemical environment. Hydrogel 'artificial muscles' 7 can generate huge dimensional changes in response to changes in temperature 8 , pH 9 , solvent 10 and electric fields 11 . Polymer conformation changes are also accompanied by large changes in equilibrium water content (EWC) of the gel, which can conveniently be measured gravimetrically. Many examples of changes in EWC with changes in pH are available in the literature, for example in the gels based on chitosan 12 .Various applications for actuating gels have been proposed, with the microscopic devices seeming most promising owing to their reasonable response times 13 . In practical applications, the influence of the external stresses on the operation of actuators cannot be neglected. Changes in mechanical properties such as

show abstract

“…The relationship between actuation strain and applied isotonic stress has been analysed previously for neat PPy actuators. 35,36 In these systems the change in elastic modulus of the PPy before and after actuation causes a length strain that usually opposes the inherent actuation. The analysis described by equation (b) suggests that increasing applied pre-strain/stress will decrease the actuation strain linearly.…”

Section: Resultsmentioning

confidence: 99%

Polypyrrole stretchable actuators

Zheng

Alici

Clingan

et al. 2012

J Polym Sci B Polym Phys

Self Cite

View full text Add to dashboard Cite

Here, we report a simple way to prepare stretchable polypyrrole (PPy)-based actuator materials that can be operated over a wide dynamic strain range and generate useable actuation displacements and pressures. The stretchable actuators were prepared as a laminated composite of PPy and a gold-coated roughened rubber sheet. By manipulating the corrugated surface of the rubber substrate, the stretchability of PPy was greatly improved. Gold-coated rubbers could be stretched to 30 percent without significant change in electrical resistance. The corrugated PPy/gold/rubber laminates successfully showed -1 percents of actuation strain even when prestretched to 24 percent. The actuation strains were smaller than for similar free-standing PPy films and a detailed analysis of the effects of corrugation and of the rubber substrate are presented to predict actuation strain under various prestretch strains. Correspondence to: Geoffrey M Spinks (E-mail: gspinks@uow.edu.au) (Additional Supporting Information may be found in the online version of this article.) ABSTRACTHere we report a simple way to prepare stretchable polypyrrole (PPy) based actuator materials that can be operated over a wide dynamic strain range and generate useable actuation displacements and pressures. The stretchable actuators were prepared as a laminated composite of polypyrrole and a gold-coated roughened rubber sheet. By manipulating the corrugated surface of the rubber substrate, the stretchability of PPy was greatly improved. Gold-coated rubbers could be stretched to 30% without significant change in electrical resistance. The corrugated PPy/gold/rubber laminates successfully showed ~1% of actuation strain even when pre-stretched to 24%. The actuation strains were smaller than for similar free-standing PPy films and a detailed analysis of the effects of corrugation and of the rubber substrate are presented to predict actuation strain under various pre-stretch strains.

show abstract

Work-per-cycle analysis for electromechanical actuators

Cited by 58 publications

References 18 publications

Force generation from polypyrrole actuators

Force generation from polypyrrole actuators

Surprising shrinkage of expanding gels under an external load

Polypyrrole stretchable actuators

Contact Info

Product

Resources

About