Liquid Crystal Elastomer Waveguide Actuators

Kuenstler, Alexa S.; Kim, Hyunki; Hayward, Ryan C.

doi:10.1002/adma.201901216

Cited by 71 publications

(54 citation statements)

References 51 publications

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“…Recently, we introduced a method to spatially pattern gold nanoparticles (AuNPs) in LCE fibers [ 43 ] and hydrogel sheets [ 44 ] with high spatial resolution using UV‐induced photoreduction of gold salt. [ 45,46 ] Following patterning, exposure to visible light induces localized photothermal deformation that drives shape‐morphing.…”

Section: Figurementioning

confidence: 99%

“…To impart photoresponsiveness, gold nanoparticles (AuNPs) are produced by in‐situ photoreduction of gold salt within the preformed LCE films as previously reported. [ 43 ] LCE samples are swollen with a solution of HAuCl 3 , oleylamine, and photoinitiator and exposed to UV light through a photomask to produce AuNPs via photochemical reduction ( Figure A). Because the degree of gold reduction is controlled by the dose of UV light, the resulting absorbance of the nanocomposite can be spatially programmed using grayscale photomasks (Figure 1B).…”

Section: Figurementioning

confidence: 99%

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Blueprinting Photothermal Shape‐Morphing of Liquid Crystal Elastomers

et al. 2020

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studies have focused on programming desired 3D structures of soft materials such as shape-memory polymers [2,3] and gels [4][5][6][7] by introducing spatial variations in thermal expansion/contraction, swelling, or molecular order. [8] A particularly useful class of materials to achieve dynamic 2D to 3D shape transformations are liquid crystal elastomers (LCEs), where the coupling between the orientational ordering of polymerized mesogens and the conformation of a polymer backbone can be leveraged for large, anisotropic deformations that are dictated by the director field. [9,10] Using oriented surface alignment layers [11] or microchannels, [12] director orientation can be patterned with a resolution approaching 10 µm. [13] A subsequent reduction of nematic ordering, usually driven by heating, leads to local contraction along the director and expansion along the transverse directions, driving out-of-plane buckling into 3D shapes that are "blueprinted" by the pattern of director orientation. However, while geometric methods allow for the deduction of the necessary inplane director orientation field to generate a desired profile of Gaussian curvature, [14][15][16][17] there are a number of practical drawbacks to this approach. First, prescription of complex director fields requires significant processing, making high-throughput fabrication, and evaluation of designs challenging. Additionally, the surface alignment methods needed to specify director orientation with high spatial resolution are only amenable to certain chemistries due to the need for high mesogen content, and thus cannot be widely generalized to all LCE systems. For example, while classical LCE systems based on siloxanes, [18,19] as well as recently developed systems that rely on simple and efficient "click" chemistries, [20] offer attractive thermal and mechanical properties for shape-morphing systems, they typically only allow for alignment of the director field with coarse spatial resolution such as through application of shear stress [21][22][23] or magnetic fields. [24] To circumvent the need for a spatially varying director orientation, where the direction of deformation varies but the magnitude is constant, a potential alternative method to drive shape changes is to instead locally prescribe the magnitude of deformation within an otherwise homogeneous director field. While spatial variations in the extent of deformation have been widely employed for shape Liquid crystal elastomers (LCEs) are an attractive platform for dynamic shape-morphing due to their ability to rapidly undergo large deformations. While recent work has focused on patterning the director orientation field to achieve desired target shapes, this strategy cannot be generalized to material systems where high-resolution surface alignment is impractical. Instead of programming the local orientation of anisotropic deformation, an alternative strategy for prescribed shape-morphing by programming the magnitude of stretch ratio in a thin LCE sheet with constant director orientation is...

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Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Blueprinting Photothermal Shape‐Morphing of Liquid Crystal Elastomers

et al. 2020

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“…[8] A photo active light guiding actuator has been constructed to drive photo thermal deformations. [9] For photothermal actuation, a specific chromophore is often added to the system so that when illuminated with the proper wavelength, a mechanical response is generated. [10][11][12][13][14] Once the illumination stops, the actuator immediately returns to its initial state due to the reduction of the temperature.…”

Section: Introductionmentioning

confidence: 99%

Light Tracking and Light Guiding Fiber Arrays by Adjusting the Location of Photoresponsive Azobenzene in Liquid Crystal Networks

Liu

Pozo

Mohseninejad

et al. 2020

Advanced Optical Materials

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The integration of light tracking and light guiding within fiber arrays is an intriguing challenge. In this study, an advanced drop casting/drawing method is applied to fabricate a fiber array capable of not only performing sunflower‐inspired light tracking, but also light guiding. The fiber arrays are constructed with various liquid crystal networks by adjusting the location of photoresponsive azobenzene moieties in the polymer network to understand the correlation between the extent of photoresponse and azobenzene location. Incorporating the azobenzene in the main chain oligomer renders these fibers with advanced photoresponse in both air and water. The fibers are able to track a light source and to guide the collected light, making these responsive actuator arrays potentially attractive for advanced photovoltaic and optical elements.

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“…Another very recent example is the exploration of LCE fibers by Hayward and co‐workers. These authors prepared mechanically aligned LCE fibers with inclusion of photothermal heaters561 that are locally swollen with a gold salt solution followed by a photochemical reduction of Au 3+ to Au 0 . Photothermal heating of the fiber is induced with 532 nm laser exposure, which induces bend and repositions the waveguided light.…”

Section: Liquid Crystal Elastomers and Networkmentioning

confidence: 99%

Materials as Machines

2020

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of responsive materials as machines is in robotics. The vision, leadership, and research of Bar-Cohen is seminal in both invigorating and focusing current-day research activities to develop responsive materials [2] and implement [3] them as lightweight, dexterous, and gentle (e.g., soft) robotic elements. In this spirit, this review exhaustively details the materials, the nature of their stimuli-response, and discusses considerations for their implementation in robotic systems and subsystems.Robotics is a well-established but growing field of research. Sustained progress in both performance and functionality continue to be realized in commercial robotic systems largely based on conventional materials and their integration with mechanisms. A recent example is the Atlas robot from Boston Dynamics [4] (Figure 1a). The incorporation of stimuli-responsive materials in robotics has largely focused on component-level demonstrations to extend the performance of a subsystem (such as a hand or gripper).Stimuli-responsive materials, spanning nearly all classes of materials and size scales, are currently subject to widespread examination in corporate, government, and academic research laboratories (Figure 1b-d). [5][6][7] In some cases, these materials have already found widespread commercial implementation in end use and are comparatively mature. The materials and fundamentals of their responses are summarized in Figure 2. Shape memory alloys (SMAs) and ceramic piezoelectric materials are distinctive in that they are hard, stimuli-responsive materials. Deformation of these materials can produce large energy densities due to their inherent stiffness. Electroactive polymers (EAPs) remain a topic of considerable interest, particularly dielectric elastomer actuators (DEAs). Engineered systems are rapidly emerging and enabling performance gains in robotics, largely based on pneumatic or fluidic (such as HASEL [8] actuators) transport processes that localize deformation to generate force or produce motion. Soft materials, such as shape memory polymers (SMPs), hydrogels, and liquid crystalline polymer networks (LCNs) and elastomers (LCEs) may offer distinctive functional performance to robotic systems in allowing local control of deformation without the need for complex interfacing with mechanisms. As will be evident, each of these materials has inherent advantages and performance tradeoffs that must be considered in functional implementations. However, responsive material systems have a common obstacle to widespread use: the performance and Machines are systems that harness input power to extend or advance function. Fundamentally, machines are based on the integration of materials with mechanisms to accomplish tasks-such as generating motion or lifting an object. An emerging research paradigm is the design, synthesis, and integration of responsive materials within or as machines. Herein, a particular focus is the integration of responsive materials to enable robotic (machine) functions such as gripping, lifting, or motility (walk...

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Liquid Crystal Elastomer Waveguide Actuators

Cited by 71 publications

References 51 publications

Blueprinting Photothermal Shape‐Morphing of Liquid Crystal Elastomers

Blueprinting Photothermal Shape‐Morphing of Liquid Crystal Elastomers

Light Tracking and Light Guiding Fiber Arrays by Adjusting the Location of Photoresponsive Azobenzene in Liquid Crystal Networks

Materials as Machines

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