Programming Photoresponse in Liquid Crystal Polymer Actuators with Laser Projector

Abstract

have emerged as promising materials for fabricating soft actuators. [12][13][14] LCNs combine the anisotropy of the constituent liquid-crystal (LC) molecules and the elasticity of polymer networks, and are capable of stimuli-responsive shape change at the macroscopic scale. LCNs can be actuated by various stimuli such as light, [15] heat, [16] solvent, [17] and humidity. [18] Being a clean, remote, and precisely controllable stimulus, light is a particularly attractive energy source. [19] The light-triggered deformation of an LCN actuator is governed by the alignment distribution of the constituent liquid-crystal molecules within the polymer network, and developing methods for precise control over the director distribution in order to obtain desired photoactuation mode is an important topic of research. [14,[20][21][22] Photoalignment has proven to be a successful technique in patterning complex alignments into liquid-crystalline materials [23][24][25] and in devising on-demand actuations into LCNs. [21] The technique is based on illuminating a thin photoresponsive layer, a "command surface," [26] with linearly polarized light. Upon illumination, the photoalignment layer becomes anisotropic, thereby changing the boundary conditions experienced by the liquid-crystal molecules in the vicinity, and forcing them to align either perpendicular [27] or parallel [28] to the light polarization. Photopatterning of director orientation can be achieved by spatially modulating the light polarization, [27] or exposure through mask(s). [28,29] White and co-workers have used a laser setup to raster scan a focussed laser beam with controlled polarization across the sample, and thus achieved local control in the director distribution. [30][31][32] Also spatial light modulators and digital micromirror devices have been used for high-throughput patterning. [17,[33][34][35] These demonstrations require either prepatterned masks or relatively complex optical set-ups for programming the desired director distribution.Herein, we use a laser projector with a microelectromechanical system (MEMS)-based scanning mirror assembly (PICO, Sony) to program the liquid-crystal alignment within a monolithic LCN film. Photopatterning is achieved by projecting an arbitrary computer-generated image onto the photoalignment layer, using predefined light polarization. The projector is capable of addressing a minimum feature size of 50 µm over an area of 25 × 14 mm 2 . A series of complex photoactuators, such as defect buckling, coiling strip with gradient in pitch, four-arm gripper, and bidirectional bending in an octopod, are demonstrated by engineering different director orientations via photopatterning. The photoactuators are fabricated by polymerizing LC monomer mixtures inside LC cells that have been A versatile, laser-projector-based method is demonstrated for programming alignment patterns into monolithic films of liquid crystal polymer networks. Complex images can be photopatterned into the polymer films with sub-100 µm resolution, using relative...

Simple Synthesis of Elastomeric Photomechanical Switches That Self‐Heal

“…Using broad‐spectrum UV irradiation (320 nm < λ < 500 nm, Γ ≈ 200 mW cm −2 ), all three fingers bent along the aligned direction with the mended region remaining stationary (Figure b). We offer this demonstration as a shortcut toward constructing arbitrary shapes using PMEs without complex alignment or manipulating cross‐linking densities …”

“…We offer this demonstration as a shortcut toward constructing arbitrary shapes using PMEs without complex alignment or manipulating cross-linking densities. [48,49] In conclusion, we have presented a simple synthesis and processing approach for creating a thermoplastic polyurethane-based PME: the precursors are readily available; the polymer requires no specialty equipment to synthesize; and the PME actuators can be "cut and paste" into photo mechanical soft machines thanks to the self-healing properties. We could tune the PME compositions for mechanical and photoresponsive properties that are comparable to some conventional light-driven azobenzene-containing LCEs.…”

Photomobile Polymer Materials with Complex 3D Deformation, Continuous Motions, Self‐Regulation, and Enhanced Processability

“…The films with discrete stripes and checkerboard patterns with alternating orientation of director showed complex deformation such as accordion‐like folding and periodic buckling (Figure c,d) . A versatile patterning of alignment layers based on laser projector with a microelectromechanical system (MEMS) has been demonstrated by Priimagi and coworkers, realizing the minimum feature size of 50 µm …”

Light‐Responsive Shape‐Changing Polymers

“…An azobenzene‐based photoalignment layer was used to define the LC alignment in the film with polarization of the incident light. In another report, Priimagi co‐workers showed a laser projector–based method for programming alignment patterns into monolithic films of azobenzene‐containing LCNs (Figure b) . As a result, complex images could be patterned into the films with sub‐100 µm resolution.…”

“…b) Molecular orientation and actuation of an LCN film with alignment patterns via photochemical mechanism. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”