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Abstract Transversely curved composite shells of liquid crystal elastomer and polyethylene terephthalate with innervated electrodes present millisecond‐scale actuation with ≈200 mW electrical power inputs at low voltages (≈1 V). The molecular orientation is aligned to direct the thermomechanical work‐content to evert the native curvature. When powered, the curved structure initially remains latent and builds up strain energy. Thereafter, the work content is released in an ms‐scale impulse. The thin‐film actuators are powered against opposing loads to perform up to 10−5J of work. High speed imaging reveals tip velocities of several 100 mm s−1with powers approaching 10−4 J s−1. The design eschews bistability. After snap‐through, when the power is off, the actuator spontaneously resets to its native state. The actuation profiles are functions of the geometry and the electrical pulse patterns. The latency of actuation is reduced by powering the actuators with pulses that trigger snap‐through, allow its reset to the native state, but prevent its cooling to the ambient before subsequent actuation cycles. The actuation is harnessed in sub‐gram scale robots, including water‐strider mimicking configurations and steerable robots that can navigate on compliant (sand) and hard (slippery) surfaces. A viable template for impulsive actuation using frugal electrical power emerges.
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Torque-Dense Photomechanical Actuation
Contactless actuation powered using light is shown to generate torque densities approaching 10 N.m/kg at angular velocities ~10 2 rad/s: metrics that compare favorably against tethered electromechanical systems. This is possible even though the extinction of actinic light limits the characteristic thickness of photoresponse in polymers to tens of μm. Confinement of molecularly patterned developable shells fabricated from azobenzene-functionalized liquid crystalline polymers encodes torque-dense photoactuation. Photostrain gradients from unstructured irradiation segment this geometry into two oppositely curved regions connected by a curved crease. A monolithic curved shell spontaneously bifurcates into a jointed, arm-like mechanism that generates flexure over sweep angles exceeding a radian. Strain focusing at the crease is hierarchical: an integral crease nucleates at smaller magnitudes of the prebiased curvature, while a crease decorated with point-like defects emerges at larger curvatures. The phase-space of morphogenesis is traceable to the competition between stretch and bending energies and is parameterizable as a function of the geometry. The framework for generating repetitive torque-dense actuation from slender light-powered actuators holds broader implications for the design of soft, remotely operated machines. Here, it is harnessed in illustrative mechanisms including levers, lifters and grabbers that are powered and regulated exclusively using light.
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- PAR ID:
- 10201585
- Date Published:
- Journal Name:
- Soft Matter
- ISSN:
- 1744-683X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0SM01352H
