In recent years, light‐responsive liquid crystal (LC) polymers have been studied as promising materials for the fabrication of untethered soft actuators. The underwater behavior of these advanced ...materials has, however, been rarely investigated. This paper reports on the fabrication of light‐responsive amphibious LC‐actuators via direct ink writing (DIW). The actuators present two underwater deformation modes triggered by different stimuli. Temperature induces contraction/expansion and light induces bending/unbending. Unexpectedly, temperature can regulate the bending directionality, giving the material additional versatility to its deformation modes. These findings serve as a toolbox for the fabrication of light‐responsive actuators via DIW that operate in air and underwater.
A liquid crystalline‐ink suitable for direct ink writing is reported. The ink results in a stimuli‐responding polymer network that bends upon light illumination in which the directionality is temperature controlled. Using this ink, an amphibious light‐responsive liquid crystalline film isfabricated via direct ink writing. The results serve as an inspiration to develop novel light‐fueled 4D actuators.
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.
Light tracking and light guiding properties are employed in fiber arrays capable of bending and unbending upon the irradiation of UV and visible light, respectively. Among various fiber arrays, those incorporating azobenzenes in the main chain oligomer generate an extraordinary photoresponse at ambient temperature in both air and water.
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.
With the advent of direct laser writing using two-photon polymerization, the generation of high-resolution three-dimensional microstructures has increased dramatically. However, the development of ...stimuli-responsive photoresists to create four-dimensional (4D) microstructures remains a challenge. Herein, we present a supramolecular cholesteric liquid crystalline photonic photoresist for the fabrication of 4D photonic microactuators, such as pillars, flowers, and butterflies, with submicron resolution. These micron-sized features display structural color and shape changes triggered by a variation of humidity or temperature. These findings serve as a roadmap for the design and creation of high-resolution 4D photonic microactuators.
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.
Over the past decade, progress in direct laser writing by two‐photon polymerization (DLW‐TPP) of stimuli‐responsive materials has made considerable inroads into the realization of microactuators. ...With the focus on performing complex tasks such as walking, grasping, or delivering drugs, these actuators require a controlled preprogrammed actuation. Liquid crystalline microactuators enable such programmed movement when the mesogenic alignment can be successfully controlled. To date, this has necessitated low crosslink density networks, which are not readily conducive to the fabrication of 3D geometries. Herein, a liquid crystalline photoresist is reported, which results in a highly crosslinked network, that permits fabrication of 4D microactuators having a highly crosslinked network in which the molecular alignment is determined by the alignment layers in the cell construct. In addition to controllable deformation of the microactuators, they also display a characteristic and unique polarization color that can be used for both identification and reporting in real time, enabling their integration into sensing and anti‐anticounterfeiting microdevices.
Untethered microactuators hold enormous potential for applications in fields spanning medicine to microfluidics. Their miniaturization still remains a challenge, specially when specific geometries displaying preprogrammed deformations are desired. Here, a liquid crystalline photoresist with a high fraction of crosslinkers is reported and the structural and optical responses of several temperature responsive 3D constructs are studied.
An optical time–temperature steam sensor is presented based on the loss of structural color in a supramolecularly cross-linked cholesteric liquid crystal photonic coating. A gradual decrease in the ...selective reflection band is observed upon exposure to temperatures above 105 °C related to the cholesteric to isotropic transition temperature. The linear polymers with carboxylic acid side chains provide physical cross-linking through hydrogen bonding that allows a time–temperature-dependent order loss through the dynamic equilibrium between supramolecular dimer and free monomer states. Steam is accelerating the color loss, and autoclave experiments show that the photonic supramolecular polymer is applicable as a steam sterilization sensor for medical applications.
Multiple samples are required to monitor and optimize the quality and reliability of quantitative measurements of stimulated emission depletion (STED) and confocal microscopes. Here, we present a ...single sample to calibrate these microscopes, align their laser beams and measure their point spread function (PSF) in 3D. The sample is composed of a refractive index matched colloidal crystal of silica beads with fluorescent and gold cores. The microscopes can be calibrated in three dimensions using the periodicity of the crystal; the alignment of the laser beams can be checked using the reflection of the gold cores; and the PSF can be measured at multiple positions and depths using the fluorescent cores. It is demonstrated how this sample can be used to visualize and improve the quality of STED and confocal microscopy images. The sample is adjustable to meet the requirements of different NA objectives and microscopy techniques and additionally can be used to evaluate refractive index mismatches as a function of depth quantitatively.
To improve access to a key synthetic intermediate we targeted a direct hydrobromination-Negishi route. Unsurprisingly, the anti-Markovnikov addition of HBr to estragole in the presence of AIBN proved ...successful. However, even in the absence of an added initiator, anti-Markovnikov addition was observed. Re-examination of early reports revealed that selective Markovnikov addition, often simply termed "normal" addition, is not always observed with HBr unless air is excluded, leading to the rediscovery of a reproducible and scalable initiator-free protocol.
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