Recent years have seen major advances in the developments of both additive manufacturing concepts and responsive materials. When combined as 4D printing, the process can lead to functional materials ...and devices for use in health, energy generation, sensing, and soft robots. Among responsive materials, liquid crystals, which can deliver programmed, reversible, rapid responses in both air and underwater, are a prime contender for additive manufacturing, given their ease of use and adaptability to many different applications. In this paper, selected works are compared and analyzed to come to a didactical overview of the liquid crystal‐additive manufacturing junction. Reading from front to back gives the reader a comprehensive understanding of the options and challenges in the field, while researchers already experienced in either liquid crystals or additive manufacturing are encouraged to scan through the text to see how they can incorporate additive manufacturing or liquid crystals into their own work. The educational text is closed with proposals for future research in this crossover field.
Liquid crystals are the basis for many “smart” materials used in, for instance, soft robotics and polymer optics. Recently, their potential and appeal for different additive manufacturing techniques has been demonstrated. Insight into the usage of liquid crystals in 3D printing for fabrication at both micro‐ and centimeterscale is provided for those wanting to join this exciting, developing field.
The iridescence of structural color and its polarization characteristics originate from the nanoscale organization of materials. A major challenge in materials science is generating the bright, ...lustrous hues seen in nature through nanoscale engineering, while simultaneously controlling interaction of the material with different light polarizations. In this work, a suitable chiral nematic liquid crystal elastomer ink is synthesized for direct ink writing, which self‐assembles into a chiral photonic structure. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis, which exhibits atypical iridescence and polarization selectivity. After crosslinking, a freely programmable, chiroptical photonic polymer material is obtained. The strongly perspective‐dependent appearance of the material can function as specialized anticounterfeit markers, as optical elements in decorative iridescent coatings, or, as demonstrated here, in optically based signaling features.
Inspired by natural examples of patterned iridescence, an ink based on a chiral nematic liquid crystal that can be processed with a direct ink writer 3D printer is shown. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis that exhibits atypical iridescence and polarization selectivity.
A supertwist liquid crystalline luminescent solar concentrator (LSC) “smart” window is fabricated which can be switched electrically between three states: one designed for increased light absorption ...and electrical generation (the “dark” state), one for transparency (the “light” state), and one for enhanced haziness (“scattering” state). In the scattering state, the absorption and edge emissions decrease while the face emissions are enhanced. This new LSC “smart” window state can find application as a privacy feature in housing, but could also allow for a new “smart” window application as a diffuse glazing to increase plant growth in horticultural applications.
A three‐state luminescent solar concentrator “smart” window is described which, along with the normal dark and light states, introduces a scattering state. This additional hazy state could find use in greenhouse horticulture applications as well as acting as a “privacy” state window capable of generating electricity via edge‐attached photovoltaic cells.
Liquid crystalline networks have been fashioned into thin films with tapered thicknesses, revealing the possibility of rolling up extremely tightly when triggered thermally or with light. Compared to ...the often limited bending shown previously in liquid crystal network actuators, these tapered films curl up several hundreds of degrees. Finite element results of simulated functionally graded thin films with tapered thicknesses corroborate well with experimental work.
Tight bending bio-inspired soft actuators were fashioned in liquid crystalline networks by using a novel tapered film geometry.
Temperature‐responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor–acceptor pair in a liquid crystalline solvent ...can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color‐tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.
FRET‐hot solar energy collection: A novel fluorescent dye was placed in a liquid‐crystal‐based luminescent solar concentrator to create a supramolecular FRET pair showing an inverse thermal response. At low temperature, no energy transfer is detected and the device is green; after heating, the acceptor becomes active and a red emission is visible.
Soft actuators allowing multifunctional, multishape deformations based on single polymer films or bilayers remain challenging to produce. In this contribution, direct ink writing is used for ...generating patterned actuators, which are in between single- and bilayer films, with multifunctionality and a plurality of possible shape changes in a single object. The key is to use the controlled deposition of a light-responsive liquid crystal ink with direct ink writing to partially cover a foil at strategic locations. We found patterned films with 40% coverage of the passive substrate by an active material outperformed “standard” fully covered bilayers. By patterning the film as two stripes, a range of motions, including left- and right-handed twisting and bending in orthogonal directions, could be controllably induced in the same actuator. The partial coverage also left space for applying liquid crystal inks with other functionalities, exemplified by fabricating a light-responsive green reflective actuator whose reflection can be switched “on” and “off”. The results presented here serve as a toolbox for the design and fabrication of patterned actuators with dramatically expanded shape deformation and functionality capabilities.
Direct Ink Writing of 4D Structural Colors Sol, Jeroen A. H. P.; Smits, Luc G.; Schenning, Albert P. H. J. ...
Advanced functional materials,
07/2022, Letnik:
32, Številka:
30
Journal Article
Recenzirano
Odprti dostop
Additive manufacturing with stimuli‐responsive materials—4D printing—is a rapidly growing field, with direct ink writing allowing deposition of a wide variety of materials. The synthesis of a ...humidity‐sensitive cholesteric liquid crystal oligomer ink is reported. With the responsive cholesteric ink, demonstrator devices exhibiting the ink's “four dimensionality” are printed in disparate fashions: as a structural color change or as a preprogrammed deformation mode. After printing, the photonic ink changes color in response to atmospheric humidity, demonstrated as a hydrochromic coating precisely deposited atop a 3D‐printed beetle. After activation in aqueous acid, the beetle exhibits vibrant color shifts across the visible spectrum. Alternatively, a scallop‐inspired actuator with a 3D‐programmed structural color is selectively treated with acid, to allow reversible “opening” and “closing” when exposed to humid and dry air, respectively. The ink enables additive manufacturing of both monolithic and multimaterial stimuli‐responsive, shape‐changing, structurally colored objects, toward broad application of cholesterics in future “smart,” 4D structurally colored devices.
Inspired by natural examples of hydrochromicity, an ink is developed to “4D print” objects with environmentally responsive structural colors. The devices designed using this ink exploit their reversible response to water in two distinct manners: as color or shape changes.
Multi‐stimuli responsivity in 3D‐printed objects is receiving much attention. However, the simultaneous interplay between different environmental stimuli is largely unexplored. In this work, we ...demonstrate direct ink writing of an oligomeric ink containing an azobenzene photo‐switch with an accessible hydrogen bond allowing triple responsivity to light, heat, and water. The resulting printed liquid crystal elastomer performs multiple actuations, the specific response depending on the environmental conditions. Bilayer films formed by printing on a static substrate can rapidly change shape, bending almost 80 degrees if irradiated in air or undergoing a shrinkage of about 50 % of its length when heated. The bilayer film assumes dramatically different shapes in water depending on combined environmental temperature and lighting conditions.
This work describes the synthesis of a new azobenzene molecule which, when incorporated in a liquid crystal elastomer, allows responsivity to environmental changes in lighting, temperature, and hydration. The underwater actuation behavior of bilayer films of the elastomer deposited on thin, inert polymer substrates depends on the combination of lighting conditions temperature of the aqueous environment.
Untethered soft actuators are usually based on 3D engineered special polymers such as liquid crystal networks or hydrogels that require complex fabrication methods. Here, an easy‐to‐process, ...anisotropic composite soft actuator based on a simple photothermal dye‐doped polyethylene film is presented. The 3D anisotropic polymer films are prepared by solution‐casting and subsequent thermal solid‐stretching. The resulting soft actuators exhibit large and controllable bending in response to light (UV and/or near‐infrared (NIR)) and are able to act as grippers picking up cargo. Additionally, the films are capable of realizing “diving” and “surfing” locomotion in and over a liquid via the photothermal induced Marangoni effect, yielding a NIR light‐fueled transporter able to pick up cargo. The results open up new possibilities of using commodity polymers in a broad range of applications including untethered soft actuators and robotic devices.
3D anisotropic single‐layer polyethylene composite films are fabricated. Such films can be used to fabricate light‐responsive actuators, grippers, surfers, and transporters. This work opens up innovative possibilities to use commodity polymers in a broad range of applications such as untethered soft actuators and robotic devices.
Luminescent solar concentrators are relatively inexpensive devices proposed to collect, convert, and redirect incident (sun)light for a variety of potential applications. In this work, dichroic dyes ...are embedded in a liquid crystal elastomer matrix and used as feedstock for direct ink writing. Direct ink writing is a promising and versatile application technique for arbitrarily aligning the dichroic dyes over glass and poly(methyl methacrylate) lightguide surfaces. The resulting prints display anisotropic edge emissions, and suggest usage as striking visual objects, combining localized color and intensity variations when viewed through a polarizer.
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