Stacking nematic elastomers for artificial muscle applications

Spillmann, Christopher M.; Naciri, Jawad; Martin, Brent R.; Farahat, Waleed A.; Herr, Hugh M.; Ratna, Banahalli R.

doi:10.1016/j.sna.2006.04.045

Cited by 50 publications

(33 citation statements)

References 21 publications

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“…Similar changes have been demonstrated in hydrogels [157]. These systems can deliver rapid large shape changes, stresses of 130 kPa have been reported for thermal actuation [158], which is enough to be useful as actuators.…”

Section: Lc Elastomerssupporting

confidence: 67%

Polymer Gel Actuators: Fundamentals

Calvert

2009

Biomedical Applications of Electroactive Polymer Actuators

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One view of materials development is to search for what materials correspond to empty spaces on a hypothetical multi-dimensional map of the properties of available materials. Following a biomimetic philosophy, for instance, it can be seen that tough ceramics and moldable short fiber composites with high moduli are possible but absent from the list of available synthetic materials. Likewise artificial muscle is missing, where the properties are defined as a developed stress of over 300 kPa, a linear contraction of 25 % and a response time of below one second. Currently dielectric elastomers come closest but have disadvantages [1,2].The actin-myosin muscle system provides the performance target for electroactive polymer actuators [3,4]. The process is driven chemically by the energy change from hydrolysis of the polyphosphate bond as ATP (adenosine triphosphate) binds to myosin and is converted to ADP (adenosine diphosphate) and phosphate. A simple chemical analogy suggests that muscle-like gels should be feasible but it is now clear that the task is much harder than it seems.Early work on gel actuation by Katchalsky-Katzir demonstrated that engines could be built using the chemical energy in diluting a lithium bromide solution to drive contraction and expansion of a collagen belt [5]. In essence, the collagen expands to take up the salt solution or contract to exclude the water. This change is both a molecular conformation change and a volume change. Other chemically driven gels, for instance polyacrylic acid fibers [6] which respond to a pH change, also rely on a solubility change giving rise to a volume change.

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Section: Lc Elastomerssupporting

confidence: 67%

Polymer Gel Actuators: Fundamentals

Calvert

2009

Biomedical Applications of Electroactive Polymer Actuators

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“…As the latter can be controlled by a number of external stimuli such as temperature, electric field, or ultraviolet light in the case of photo-responsive azobenzene-based elastomers, LCE have great potential for application in various sensing devices, as well as for actuation (1,2). The applications of such actuators are fascinating, ranging from artificial muscles, heart valves, and other biomedical applications (3)(4)(5)(6)(7)(8), to micro-and nano-electromechanical (2), as well as electrooptical systems like adaptive lenses (3,9), where their high deformability and low weight make them particularly promising. Among the possible actuation stimuli the external electric field is particularly appealing, even if quite difficult to implement since a rather strong field is required to induce deformations.…”

mentioning

confidence: 99%

Molecular simulations elucidate electric field actuation in swollen liquid crystal elastomers

Skačej

Zannoni

2012

Proc. Natl. Acad. Sci. U.S.A.

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Swollen elastomer liquid crystals undergo significant deformations by application of an electric field perpendicular to their alignment axis, as shown in experiments by Urayama et al. [Urayama K, Honda S, Takigawa T (2006) Macromolecules 39:1943-1949]. Here we clarify this surprising effect at the molecular level using largescale Monte Carlo simulations of an off-lattice model based on a soft Gay-Berne potential. We provide the internal change of molecular organization, as well as the key observables during the actuation cycle.actuators | nematic rubbers | orientational stripe domains | microscopic modeling L iquid crystal elastomers (LCE) are rubbery functional materials consisting of weakly cross-linked polymer strands with embedded liquid crystalline (mesogenic) units. This unique microscopic design provides a pronounced coupling between macroscopic strain and the underlying mesogenic orientational order (1). As the latter can be controlled by a number of external stimuli such as temperature, electric field, or ultraviolet light in the case of photo-responsive azobenzene-based elastomers, LCE have great potential for application in various sensing devices, as well as for actuation (1, 2). The applications of such actuators are fascinating, ranging from artificial muscles, heart valves, and other biomedical applications (3-8), to micro-and nano-electromechanical (2), as well as electrooptical systems like adaptive lenses (3, 9), where their high deformability and low weight make them particularly promising. Among the possible actuation stimuli the external electric field is particularly appealing, even if quite difficult to implement since a rather strong field is required to induce deformations. This problem can be partly overcome by focusing on the so-called (semi)soft deformation modes, e.g., liquid crystalline director rotation accompanied by shear, where significant strain can be achieved at a rather low free energy cost (10-14).More recently, actuation has been implemented experimentally in unconstrained swollen samples by applying an external electric field perpendicular to the director, using optical and infrared spectroscopy techniques to detect changes in mesogenic ordering (15)(16)(17). These experiments were rationalized by a theoretical study based on the semisoft neoclassical free energy (18), as well as by a continuum treatment of the electro-opto-mechanical effect dynamics (19). On the other hand, little has been done so far to obtain a deeper molecular-level insight into the actuation-related phenomena in LCE. For example, we have carried out an early microscopic lattice simulation attempt (20), which, however, lacking translational molecular degrees of freedom, turned out to have only limited predictive power because of inevitable assumptions regarding the strain-alignment coupling. As this and several other issues can be safely bypassed within a more demanding microscopic description based on pairwise intermolecular interactions, we have recently implemented an off-lattice molecular simulati...

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“…This effect is the so-called thermo-mechanical effect (Figure 6a and 7). [32][33][34][35][36] The introduction of photo-sensitive azoderivatives in LSCEs, not only as side-chain groups but as cross-linkers as well, affords a new way to control the macroscopic dimensions of the sample isothermally just by applying light. So, azobenzene-containing LSCEs are very attractive materials for the fabrication of light-controlled artificial muscle-like actuators.…”

Section: Liquid-crystalline Elastomers For Light-induced Artificial Mmentioning

confidence: 99%