4D Printing of a Liquid Crystal Elastomer with a Controllable Orientation Gradient

Abstract

Liquid crystal elastomers (LCEs), a class of soft materials capable of a large and reversible change in the shape under the trigger of external stimuli, can be fabricated into diverse architectures with complicated deformation modes through four-dimensional (4D) printing. However, the printable LCE ink is only in the form of monomeric precursors and the deformation mode is limited to contraction/extension deformation. Herein, we report a novel approach to break through these limitations. We achieved 4D printing of a single-component liquid crystal polymer ink in its isotropy state through direct ink writing (DIW) technology. The drawing force imposed by the movement of nozzle in the extruded printing process was able to align the mesogen units along the specific printing path. An orientation gradient perpendicular to the printing direction was obtained due to the existence of a temperature gradient between the two sides of printed samples and could be further fixed by post-photo-cross-linking treatment through the dimerizable groups in the LCE, realizing a new actuation mode in the field of extrusion-based printing of LCE actuators. The printed film was able to change reversibly from a strip to a tightly hollow cylinder and could reversibly lift up an object with roughly 600 times its own weight. The orientation gradient can be patterned through liquid-assistant printing or programmed structure design to integrate both bending and contraction actuation modes on the same printed sample, leading to complex deformation and two-dimensional (2D) planar porous structure to three-dimensional (3D) porous cylinder transition. This study opens up a new prospect to directly print a wide variety of LCE actuators with versatile actuation modes.

Plasma‐Induced Polymerizations: A New Synthetic Entry in Liquid Crystal Elastomer Actuators

“…However, surface‐anchoring technologies have limitation in sample thickness, and the reported LCE films have thickness of <200 µm. On the other hand, sequential or gradient cross‐linking, [ 22,39,40 ] 3D printing, [ 41 ] and photolithography [ 42,43 ] were also employed to make complex LCEs with 3D deformations. In particular, 3D printing as an emerging technology to prepare LCEs allows to prepare sophisticated LCE structures.…”

3D Microstructures of Liquid Crystal Networks with Programmed Voxelated Director Fields

“…Indeed, 3D‐to‐3D shape transformations have become viable either through simple molding, embossing, and selective photo‐crosslinking of pre‐polymerized LCE gels [ 38–40 ] or by single‐ or multi‐material 3D printing of LCE inks. [ 41–45 ] Nevertheless, the molecular orientation in all these examples is controlled rather globally and mainly by the stretching and shear extrusion of the pre‐polymerized LCE precursors.…”

Smart polymers and nanocomposites for 3D and 4D printing

“…Using this approach various 2D architectures were printed which were able to undergo a 2D-to-3D shape morphing in response to heating above TNI [232]. Temperature gradient across the thickness of the printed layers can be used to provide an orientation gradient of the mesogen unites within the printed parts which enables more complicated shape shifting [234]. Fig.7: 4D printing of thermo-responsive SMPs; a) SLA printed shape memory structures with macromethacrylate [196].…”