An Untethered Magnetic‐ and Light‐Responsive Rotary Gripper: Shedding Light on Photoresponsive Liquid Crystal Actuators

Abstract

materials and is desired for untethered multi-responsive soft robotics, opening a new range of applications, expanding from remotely controlled motion to possible locomotion. However, a facile approach to combining multi-stimulus response into one device without imposing dramatic mechanical or chemical changes to the system remains a challenge. Grasping devices making use of stimuli-responsive actuation have already been reported [9][10][11][12][13][14][15] and a present goal in this field is to free these stimuli-responsive soft robotic grippers from the necessity of manual manipulation for movement.Combining soft materials and stimuliresponsive reagents for the development of functional materials is a present endeavor. [16] Liquid crystal networks (LCNs) are attractive materials for fabricating soft actuators since they operate in dry environments, and their deformation can be programmed within the LC network by the 3D organization of the molecular building blocks. The versatility of liquid crystal (LC) networks has allowed for the development of several functional, responsive actuators with diverse fabrication techniques, such as 3D printing, [17] and operating with a variety of triggers, including light, [18][19][20][21][22] heat, [23] humidity, [24,25] and magnetic, [26,27] and electric [28] fields. Among the triggers studied in the development of LC actuators, light is highly appealing for untethered motion as it provides instantaneous stimulus, resulting in a fast response Here, a remotely controlled dual magneto-and photoresponsive soft robotic gripper is reported, capable of loading, transport, rotation, and release of cargo. The untethered soft actuator consists of a magnetically responsive polydimethylsiloxane layer containing magnetic iron powder coated onto the central region of a light-responsive liquid crystal polymer film hosting photochromic azobenzene dyes. Light is used to trigger the actuator to autonomously grab and pick up cargo with a high degree of control. Magnetic response is employed to conduct the locomotion as magnetic guidance, allowing the gripper to have both translational freedom and rotational freedom in its locomotion, differentiating the device from other soft robotic grippers. Control can be attained even in enclosed and/or confined spaces, through solely remote actuation. Through combined video, mechanical, and thermal analyses, the actuation mechanism of the light-responsive liquid crystal network is investigated, shedding light on the decisive role of the temperature evolution in governing both rate of motion and deformation amplitude of the light-responsive soft actuator.

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…The thermoplastic actuator was fabricated using a scalable spray‐coating method, depositing the light‐responsive LCs from xylene on a biaxially stretched 12 μm thick PET polymer (Figure S1 in the Supporting Information) . The sprayed nematic LC mixture (Figure S2) self‐aligned in a splay molecular alignment on the PET, see Figure S3 .…”

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…The thermoplastic actuator was fabricated using a scalable spray-coating method, depositing the light-responsive LCs from xylene on a biaxially stretched 12 mm thick PET polymer ( Figure S1 in the Supporting Information). [36][37][38] The sprayed nematic LC mixture ( Figure S2) self-aligned in a splay molecular alignment on the PET, see Figure S3. [37] The LC mixture was photopolymerized in the nematic phase at 85 8C for 10 minutes in an inert nitrogen atmosphere ( Figure S4).…”

On Untethered, Dual Magneto‐ and Photoresponsive Liquid Crystal Bilayer Actuators Showing Bending and Rotating Motion

“…The bilayer actuator consists of a photoresponsive LCN (20 µm in thickness) and a PDMS layer of varying thicknesses (50, 130, and 210 µm). The liquid crystal polymer is a splay aligned network, composed of two LC monomers (M1, 56.5 mol% and M2, 40.5 mol%,), a photo responsive azobenzene dopant (A1, 2 mol%) and a photoinitiator (PI, 1 mol%) (Figure S1, Supporting Information): film preparation follows previously reported methods . In splay alignment, the LC molecules at the opposing surfaces of the film have different orientations: one has a planar alignment in which the molecules are oriented parallel to the surface, and the other a homeotropic with molecules aligned perpendicular to the surface (Figure A).…”

“…In our previous work, we revealed the mechanism for the light triggered response of a liquid crystal network doped with a fast isomerizing azobenzene . The single films studied display an unbending actuation upon illumination from a precurled shape into an extended film, the actuation motion independent from the illumination direction.…”