Dual-Wavelength Volumetric Microlithography for Rapid Production of 4D Microstructures

4D microstructured actuators are micro-objects made of stimuli-responsive materials capable of induced shape deformations, with applications ranging from microrobotics to smart micropatterned haptic surfaces. The novel technology dual-wavelength volumetric microlithography (DWVML) realizes rapid printing of high-resolution 3D microstructures and so has the potential to pave the way to feasible manufacturing of 4D microdevices. In this work, DWVML is applied for the first time to printing stimuli-responsive materials, namely, liquid crystal networks (LCNs). An LCN photoresist is developed and characterized, and large arrays of up to 5625 LCN micropillars with programmable shape changes are produced by means of DWVML in the time span of seconds, over areas as large as ∼5.4 mm2. The production rate of 0.24 mm3 h-1 is achieved, exceeding speeds previously reported for additive manufacturing of LCNs by 2 orders of magnitude. Finally, a membrane with tunable, micrometer-sized pores is fabricated to illustrate the potential DWVML holds for real-world applications.

Fully (Re)configurable Interactive Material through a Switchable Photothermal Charge Transfer Complex Gated by a Supramolecular Liquid Crystal Elastomer Actuator

Charge transfer complexes (CTCs) based on self-assembled donor and acceptor molecules allow light absorption of significantly redshifted wavelengths to either the donor or acceptor. In this work, we demonstrate a CTC embedded in a hydrogen-bonded liquid crystal elastomer (LCE), which in itself is fully reformable and reprocessable. The LCE host acts as a gate, directing the self-assembly of the CTC. When hydrogen bonding is present, the CTC behaves as a near-infrared (NIR) dye allowing photothermal actuation of the LCE. The CTC can be disassembled in specific regions of the LCE film by disrupting the hydrogen bond interactions, allowing selective NIR heating and localized actuation of the films. The metastable non-CTC state may persist for weeks or can be recovered on demand by heat treatment. Besides the CTC variability, the capability of completely reforming the shape, color, and actuation mode of the LCE provides an interactive material with unprecedented application versatility.

Switching between 3D Surface Topographies in Liquid Crystal Elastomer Coatings Using Two-Step Imprint Lithography

While dynamic surface topographies are fabricated using liquid crystal (LC) polymers, switching between two distinct 3D topographies remains challenging. In this work, two switchable 3D surface topographies are created in LC elastomer (LCE) coatings using a two-step imprint lithography process. A first imprinting creates a surface microstructure on the LCE coating which is polymerized by a base catalyzed partial thiol-acrylate crosslinking step. The structured coating is then imprinted with a second mold to program the second topography, which is subsequently fully polymerized by light. The resulting LCE coatings display reversible surface switching between the two programmed 3D states. By varying the molds used during the two imprinting steps, diverse dynamic topographies can be achieved. For example, by using grating and rough molds sequentially, switchable surface topographies between a random scatterer and an ordered diffractor are achieved. Additionally, by using negative and positive triangular prism molds consecutively, dynamic surface topographies switching between two 3D structural states are achieved, driven by differential order/disorder transitions in the different areas of the film. It is anticipated that this platform of dynamic 3D topological switching can be used for many applications, including antifouling and biomedical surfaces, switchable friction elements, tunable optics, and beyond.

Photonic Liquid Crystal Polymer Absorbent for Immobilization and Detection of Gaseous Nerve Agent Simulants

Detection and sequestration of chemical warfare agents (CWAs), such as poisonous organophosphates, are highly desirable for both personal security and environmental protection. However, both sensing and absorption in a single device have been rarely reported. In this study, we describe a photonic absorbent based on a cholesteric liquid crystal polymer as a dual sensing and decontamination device for gas-type CWAs. Dimethyl methylphosphonate (DMMP) was used as a simulant compound. A blue reflective photonic polymer was fabricated that was able to detect DMMP vapor through absorption. Hydrogen bond interactions between DMMP and mesogenic carboxylic groups of the polymer allow selectivity and capture. A distinct optical change of the film from blue to bright green indicates the absorption of DMMP vapor molecules and confirms when full absorption of the polymer is achieved. The diffusion of DMMP vapor into the material was observed by the formation of a sharp boundary between swollen and unswollen material, as evidenced by scanning electron microscopy images and the structural color changes. In ambient conditions, DMMP molecules are retained in the photonic absorbent without release to the environment. Heating above approximately 60 °C releases the absorbed DMMP, leading to a reusable optical device. These results confirm the ability of photonic polymers to sense and immobilize dangerous vapor, paving the way for the realization of simple, battery-free optical devices able to simultaneously warn and protect.

Rapid and Replaceable Luminescent Coating for Silicon-Based Microreactors Enabling Energy-Efficient Solar Photochemistry

The sun is the most sustainable source of photons on the earth but is rarely used in photochemical transformations due its relatively low and variable intensity, broad wavelength range, and lack of focus. Luminescent solar concentrator-based photomicroreactors (LSC-PMs) can be an answer to all these issues, but widespread adoption is plagued by challenges associated with their complicated manufacturing. Herein, we developed a new strategy to accelerate and ease the production of LSC-PMs by depositing a thin luminescent film on commercially and widely available silicon-based microreactors. The protocol is fast and operationally simple, and the luminescent coating can be easily removed and replaced. This enables rapid tuning of the luminescent coating to fit the requirements of the photocatalytic system and to increase the photon flux inside the microreactor channels.

Liquid crystal-based structural color actuators

Animals can modify their body shape and/or color for protection, camouflage and communication. This adaptability has inspired fabrication of actuators with structural color changes to endow soft robots with additional functionalities. Using liquid crystal-based materials for actuators with structural color changes is a promising approach. In this review, we discuss the current state of liquid crystal-based actuators with structural color changes and the potential applications of these structural color actuators in soft robotic devices.

Pigmented Structural Color Actuators Fueled by Near-Infrared Light

Cuttlefish can modify their body shape and both their pigmentary and structural colors for protection. This adaptability has inspired the development of appearance-changing polymers such as structural color actuators, although in most cases, the original shape has been confined to being flat, and pigmented structural color actuators have not yet been reported. Here, we have successfully created a pigmented structural color actuator using a cholesteric liquid crystal elastomer with a lower actuation temperature where both actuation and coloration (structural and pigmental) are tunable with temperature and NIR light. The shape, structural color, and absorption of the NIR-absorbing dye pigment of the actuator all change with temperature. Light can be used to trigger local in-plane bending actuation in flat films and local shape changes in a variety of 3D-shaped objects. A cuttlefish mimic that can sense light and respond by locally changing its appearance was also made to demonstrate the potential of pigmented structural color actuators for signaling and camouflage in soft robotics.

4D Printing of Liquid Crystals: What's Right for Me?

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.

Development of an Off-Grid Solar-Powered Autonomous Chemical Mini-Plant for Producing Fine Chemicals

Photochemistry using inexhaustible solar energy is an eco-friendly way to produce fine chemicals outside the typical laboratory or chemical plant environment. However, variations in solar irradiation conditions and the need for an external energy source to power electronic components limits the accessibility of this approach. In this work, a chemical solar-driven "mini-plant" centred around a scaled-up luminescent solar concentrator photomicroreactor (LSC-PM) was built. To account for the variations in solar irradiance at ground level and passing clouds, a responsive control system was designed that rapidly adapts the flow rate of the reagents to the light received by the reaction channels. Supplying the plant with solar panels, integrated into the module by placing it behind the LSC to utilize the transmitted fraction of the solar irradiation, allowed this setup to be self-sufficient and fully operational off-grid. Such a system can shine in isolated environments and in a distributed manufacturing world, allowing to decentralize the production of fine chemicals.

Patterned Actuators via Direct Ink Writing of Liquid Crystals

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.

Flower-Like Colloidal Particles through Precipitation Polymerization of Redox-Responsive Liquid Crystals

We report on the synthesis of monodisperse, flower‐like, liquid crystalline (LC) polymer particles by precipitation polymerization of a LC mixture consisting of benzoic acid‐functionalized acrylates and disulfide‐functionalized diacrylates. Introduction of a minor amount of redox‐responsive disulfide‐functionalized diacrylates (≤10 wt %) induced the formation of flower‐like shapes. The shape of the particles can be tuned from flower‐ to disk‐like to spherical by elevating the polymerization temperature. The solvent environment also has a pronounced effect on the particle size. Time‐resolved TEM reveals that the final particle morphology was formed in the early stages of the polymerization and that subsequent polymerization resulted in continued particle growth without affecting the morphology. Finally, the degradation of the particles under reducing conditions was much faster for flower‐like particles than for spherical particles, likely a result of their higher surface‐to‐volume ratio.

Liquid-Crystalline Polymer Particles Prepared by Classical Polymerization Techniques

Liquid-crystalline polymer particles prepared by classical polymerization techniques are receiving increased attention as promising candidates for use in a variety of applications including micro-actuators, structurally colored objects, and absorbents. These particles have anisotropic molecular order and liquid-crystalline phases that distinguish them from conventional polymer particles. In this minireview, the preparation of liquid-crystalline polymer particles from classical suspension, (mini-)emulsion, dispersion, and precipitation polymerization reactions are discussed. The particle sizes, molecular orientations, and liquid-crystalline phases produced by each technique are summarized and compared. We conclude with a discussion of the challenges and prospects of the preparation of liquid-crystalline polymer particles by classical polymerization techniques.

Anisotropic Iridescence and Polarization Patterns in a Direct Ink Written Chiral Photonic Polymer

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.

Hydrogen-Bonded Supramolecular Liquid Crystal Polymers: Smart Materials with Stimuli-Responsive, Self-Healing, and Recyclable Properties

Hydrogen-bonded liquid crystalline polymers have emerged as promising “smart” supramolecular functional materials with stimuli-responsive, self-healing, and recyclable properties. The hydrogen bonds can either be used as chemically responsive (i.e., pH-responsive) or as dynamic structural (i.e., temperature-responsive) moieties. Responsiveness can be manifested as changes in shape, color, or porosity and as selective binding. The liquid crystalline self-organization gives the materials their unique responsive nanostructures. Typically, the materials used for actuators or optical materials are constructed using linear calamitic (rod-shaped) hydrogen-bonded complexes, while nanoporous materials are constructed from either calamitic or discotic (disk-shaped) complexes. The dynamic structural character of the hydrogen bond moieties can be used to construct self-healing and recyclable supramolecular materials. In this review, recent findings are summarized, and potential future applications are discussed.

Monodisperse Liquid Crystalline Polymer Shells with Programmable Alignment and Shape Prepared by Seeded Dispersion Polymerization

Monodisperse, micrometer-sized liquid crystalline (LC) shells are prepared by seeded dispersion polymerization. After polymerizing LC monomer mixtures in the presence of non-crosslinked polymer seeds, hollow LC polymer shells with programmable alignment and shape are prepared by removing the seeds. The LC alignment in the LC polymer shells can be easily manipulated by the polymer seeds, as a radial alignment is observed with amorphous poly(phenyl methacrylate) seeds and a bipolar alignment is observed with bipolar LC polymer seeds. After removal of the seeds, the radially aligned samples give radially aligned shells with small dimples. The resulting bipolar LC polymer shells collapse into a biconcave shape. Polarized optical microscopy and transmission electron microscopy indicate that the collapse occurs at the defect points in the shell. In the case of a lower crosslink density, LC polymer hollow shells with larger dimples are obtained, resulting in cup-shaped polymer particles. Biconcave LC polymer shells based on other LC mixtures have also been prepared, showing the versatility of the seeded dispersion polymerization method.

Enhanced Thermal Conductivity in Oriented Polyvinyl Alcohol/Graphene Oxide Composites

Polymer composites have attracted increasing interest as thermal management materials for use in devices owing to their ease of processing and potential lower costs. However, most polymer composites have only modest thermal conductivities, even at high concentrations of additives, resulting in high costs and reduced mechanical properties, which limit their applications. To achieve high thermally conductive polymer materials with a low concentration of additives, anisotropic, solid-state drawn composite films were prepared using water-soluble polyvinyl alcohol (PVA) and dispersible graphene oxide (GO). A co-additive (sodium dodecyl benzenesulfonate) was used to improve both the dispersion of GO and consequently the thermal conductivity. The hydrogen bonding between GO and PVA and the simultaneous alignment of GO and PVA in drawn composite films contribute to an improved thermal conductivity (∼25 W m^-1 K^-1), which is higher than most reported polymer composites and an approximately 50-fold enhancement over isotropic PVA (0.3-0.5 W m^-1 K^-1). This work provides a new method for preparing water-processable, drawn polymer composite films with high thermal conductivity, which may be useful for thermal management applications.

Triple-Shape-Memory Soft Actuators from an Interpenetrating Network of Hybrid Liquid Crystals

In this work, the formation of triple-shape-memory liquid crystalline-interpenetrating polymer network (LC-IPN) actuators based on a hybrid acrylate-oxetane LC mixture is reported. Orthogonal polymerization of the oxetane and acrylate liquid crystals creates polymer films with two distinct glass-transition temperatures. The use of these two transitions for one-way triple-shape-memory actuation and two-way bending actuation with a broad temperature window for actuation is demonstrated. Our results combine shape memory polymers with liquid crystal-based soft actuators having advanced stimuli-responsive properties.

NIR-vis-UV Light-Responsive High Stress-Generating Polymer Actuators with a Reduced Creep Rate

Untethered, light-responsive, high-stress-generating actuators based on widely-used commercial polymers are appealing for applications in soft robotics. However, the construction of actuators that are stable and reversibly responsive to low-intensity ultraviolet, visible, and infrared lights remains challenging. Here, transparent, stress-generating actuators are reported based on ultradrawn, ultrahigh molecular weight polyethylene films. The composite films have different draw ratios (30, 70, and 100) and contain a small amount of graphene in combination with ultraviolet and near-infrared-absorbing dyes. The composite actuators respond rapidly (t_0.9 < 0.8 s) to different wavelengths of light (i.e., 780, 455, and 365 nm). A maximum photoinduced stress of 35 MPa is achieved at a draw ratio of 70 under near-infrared light irradiation. The photoinduced stress increases linearly with the light intensity, indicating the transfer of light into thermally induced mechanical contraction. Moreover, the addition of additives lead to a reduction in the plastic creep rate of the drawn films compared to their nonmodified counterparts.

Wavelength-Selective Photopolymerization of Hybrid Acrylate-Oxetane Liquid Crystals

We report on the wavelength-selective photopolymerization of a hybrid acrylate-oxetane cholesteric liquid crystal monomer mixture. By controlling the sequence and rate of the orthogonal free-radical and cationic photopolymerization reactions, it is possible to control the degree of phase separation in the resulting liquid crystal interpenetrating networks. We show that this can be used to tune the reflective color of the structurally colored coatings produced. Conversely, the structural color can be used to monitor the degree of phase separation. Our new photopolymerization procedure allows for structuring liquid crystal networks in three dimensions, which has great potential for fabricating liquid crystal polymer materials with programmable functional properties.

Bioinspired light-driven soft robots based on liquid crystal polymers

Nature is a constant source of inspiration for materials scientists, fueling the dream of mimicking life-like motion and tasks in untethered, man-made devices. Liquid crystalline polymers (LCPs) programmed to undergo three-dimensional shape changes in response to light are promising materials for fulfilling this dream. The successful development of autonomous, highly controlled light-driven soft robots calls for an understanding of light-driven actuation, advancements in material function and performance, and progress in engineering principles for transforming actuation into life-like motions, from simple bending to walking, for example. This tutorial review includes an introduction to liquid crystal (LC)-based materials and highlights developments in light-responsive LC polymers, shape programmability and sustained motions to finally achieve bioinspired untethered soft robots able to perform locomotion and tasks.

Stimuli-Responsive Shape Changing Commodity Polymer Composites and Bilayers

Commodity polymers are produced in large volumes, providing robust mechanical properties at relatively low costs. The products made from these commodity polymers typically offer only static functionalities. Over the past decade, however, in the scientific literature, stimuli-responsive additives and/or polymer coatings have been introduced to commodity polymers, yielding composites and bilayers that change shape in response to light, temperature, and/or humidity. These stimuli responsive commodity polymers allow the marketing and sales of these otherwise bulk products as "high-end" smart materials for applications spanning from soft actuators to adaptive textiles. This Spotlight on Applications presents an overview of recent intriguing works on how shape changing commodity polymer composite and bilayer actuators based on polyamide 6, poly(ethylene terephthalate), polyethylene, and polypropylene have been fabricated that respond to environmental stimuli and discusses their potential applications.

Epoxide and oxetane based liquid crystals for advanced functional materials

Liquid crystalline elastomers (LCEs) and liquid crystalline networks (LCNs) are classes of polymers very suitable for fabricating advanced functional materials. Two main pathways to obtain LCEs and LCNs have gained the most attention in the literature, namely the two-step crosslinking of LC side-chain polymers and the photoinitiated free-radical polymerisation of acrylate LC monomers. These liquid crystal polymers have demonstrated remarkable properties resulting from their anisotropic shapes, being used in soft robotics, responsive surfaces and as photonic materials. In this review, we will show that LCs with cyclic ethers as polymerisable groups can be an attractive alternative to the aforementioned reactive acrylate mesogens. These epoxide and oxetane based reactive mesogens could offer a number of advantages over their acrylate-based counterparts, including oxygen insensitivity, reduced polymerisation shrinkage, improved alignment, lower processing viscosity and potentially extended resistivity. In this review, we summarise the research on these materials from the past 30 years and offer a glimpse into the potential of these cyclic ether mesogens.

Programmable liquid crystal elastomer microactuators prepared via thiol-ene dispersion polymerization

Narrowly dispersed, 10 micron-sized, liquid crystalline elastomer polymer actuators were first prepared via thiol-ene dispersion polymerization and then embedded and stretched in a polyvinyl alcohol film, followed by photopolymerization of the residual acrylate groups. Prolate micro spheroids in which the mesogens are aligned parallel to the long axis were obtained and showed reversible thermally driven actuation owing to nematic to isotropic transition of the liquid crystal molecules. The particles were also compressed to form disk-shaped oblate microactuators in which the mesogens are aligned perpendicular to the short axis, demonstrating that the reported method is a versatile method to fabricate liquid crystal elastomer microactuators with programmable properties.

Unravelling humidity-gated, temperature responsive bilayer actuators

By spraying liquid crystal mixtures onto stretched polyamide 6 (PA6) substrates, dual-responsive heat/humidity bilayer actuators are generated. The oriented PA6 guides the self-organization of the liquid crystal monomers into well-aligned, anisotropic liquid crystal networks. The bilayer responds to changes in the environmental relative humidity, resulting in bending of the actuator with the liquid crystal network inside the curvature. In contrast, in conditions of constant high humidity (80%RH), increasing the temperature triggers the liquid crystal network coating to bend the bilayer in the opposing direction. The dual-responsivity to changes in environmental humidity and temperature is examined in detail and discussed theoretically to elucidate the humidity-gated, temperature responsive properties revealing guidelines for fabricating anisotropic bilayer actuators.

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo-Responsive Actuators

Arbitrary shape (re)programming is appealing for fabricating untethered shape-morphing photo-actuators with intricate configurations and features. We present re-programmable light-responsive thermoplastic actuators with arbitrary initial shapes through spray-coating of polyethylene terephthalate (PET) with an azobenzene-doped light-responsive liquid crystal network (LCN). The initial geometry of the actuator is controlled by thermally shaping and fixing the thermoplastic PET, allowing arbitrary shapes, including origami-like folds and left- and right-handed helicity within a single sample. The thermally fixed geometries can be reversibly actuated through light exposure, with fast, reversible area-specific actuation such as winding, unwinding and unfolding. By shape re-programming, the same sample can be re-designed and light-actuated again. The strategy presented here demonstrates easy fabrication of mechanically robust, recyclable, photo-responsive actuators with highly tuneable geometries and actuation modes.

A Soft Transporter Robot Fueled by Light

Mobile organisms with ability for locomotion and transportation, such as humans and other animals, utilize orchestrated actuation to perform actions. Mimicking these functionalities in synthetic, light-responsive untethered soft-bodied devices remains a challenge. Inspired by multitasking and mobile biological systems, an untethered soft transporter robot with controlled multidirectional locomotion with the ability of picking up, transporting, and delivering cargo driven entirely by blue light is created. The soft robot design is an ensemble of light-responsive liquid crystalline polymers that can harness motion either collectively or individually to obtain a high degree of motion control for the execution of advanced tasks in a dry environment. Through orchestrated motion of the device's "legs", single displacement strides, which exceed 4 mm and can be taken in any direction, allow for locomotion around objects. Untethered cargo transportation is demonstrated by a pickup and release mechanism using the device's "arms". This strategy demonstrates the constructive harnessing of orchestrated motion in assemblies of established actuators, performing complex functions, mimicking constructive behavior seen in nature.

Dual-responsive "smart" window and visually attractive coating based on a diarylethene photochromic dye

Controlling the intensity and manipulating the spectral composition of sunlight are critical for many devices including "smart" windows, greenhouses, and photomicroreactors, but these are also important in more decorative applications. Here, we use a diarylethene dye incorporated in a liquid crystal host to create a dual-responsive "smart" window regulated both by an electrical trigger and by specific wavelengths of light. By incorporating the same diarylethene dye in a polymerizable host and using inkjet printing, coatings can be made with complete freedom in the applied pattern design, although the electrical response is lost. The color change of the diarylethene dye can be controlled in simulated sunlight by concurrent light exposure from an LED source, allowing a manual override for outdoor use. Photoluminescence of the closed isomer of the diarylethene from the light guide edges could be used for lighting or electricity generation in a luminescent solar concentrator architecture.

Monodisperse Liquid Crystal Network Particles Synthesized via Precipitation Polymerization

The production of liquid crystalline (LC) polymer particles with a narrow size distribution on a large scale remains a challenge. Here, we report the preparation of monodisperse, cross-linked liquid crystalline particles via precipitation polymerization. This versatile and scalable method yields polymer particles with a smectic liquid crystal order. Although the LC monomers are randomly dissolved in solution, the oligomers self-align and LC order is induced. For the polymerization, a smectic LC monomer mixture consisting of cross-linkers and benzoic acid hydrogen-bonded dimers is used. The average diameter of the particles increases at higher polymerization temperatures and in better solvents, whereas the monomer and initiator concentration have only minor impact on the particle size. After deprotonating of the benzoic acid groups, the particles show rapid absorption of a common cationic dye, methylene blue. The methylene blue in the particles can be subsequently released with the addition of Ca²⁺, while monovalent ions fail to trigger the release. These results reveal that precipitation polymerization is an attractive method to prepare functional LC polymer particles of a narrow size distribution and on a large scale.

Energy-Efficient Solar Photochemistry with Luminescent Solar Concentrator Based Photomicroreactors

The sun is the most sustainable light source available on our planet, therefore the direct use of sunlight for photochemistry is extremely appealing. Demonstrated here, for the first time, is that a diverse set of photon-driven transformations can be efficiently powered by solar irradiation with the use of solvent-resistant and cheap luminescent solar concentrator based photomicroreactors. Blue, green, and red reactors can accommodate both homogeneous and multiphase reaction conditions, including photochemical oxidations, photocatalytic trifluoromethylation chemistry, and metallaphotoredox transformations, thus spanning applications over the entire visible-light spectrum. To further illustrate the efficacy of these novel solar reactors, medicinally relevant molecules, such as ascaridole and an intermediate of artemisinin, were prepared as well.

Implementing a Practical, Bachelor's-Level Design-Based Learning Course To Improve Chemistry Students' Scientific Dissemination Skills

This work presents an outline for a full-quartile design-based learning laboratory-based course suitable for final year Bachelor's students. The course has been run for 5 years in the department of Chemical Engineering and Chemistry. The course attempts to provide a complete laboratory experience for its students, including an authentic research project, experience in writing a research paper with realistic limitations of both space and time, and giving of a presentation appropriate for a scientific conference, finally culminating with a written exam, where the questions are based on the written reports and oral presentations of the other students, making the students also course "teachers". This article will discuss both the successful aspects of the course and point out the areas that still need improvement and provides enough information as to allow the transfer of the methodology to other educational curricula.

Air-Curable, High-Resolution Patternable Oxetane-Based Liquid Crystalline Photonic Films via Flexographic Printing

The production of patterned photonic films on a large scale remains a challenge. Here, we report on a new class of photonic materials that are based on oxetane liquid crystals (LCs). Patterned reflective coatings can be produced from these materials on flexible substrates by using flexographic printing. This industrially relevant process allows for upscaling in future applications. Furthermore, the oxetane LCs used do not require an inert atmosphere for photopolymerization, unlike previously described acrylate systems. We show that the flexographic printing process results in excellent alignment, and that the patterns produced display a high resolution. Additionally, we demonstrate that free-standing photonic reflecting foils can also be produced from these materials. Our new oxetane-based patterned iridescent colored materials have potential application for both esthetic purposes as well as anticounterfeit labels.

A self-sustained soft actuator able to rock and roll

Liquid crystalline networks of specific geometry are observed to undergo thermally triggered chaotic continual rocking motion and light triggered rolling.

Butterfly proboscis-inspired tight rolling tapered soft actuators

Tight bending bio-inspired soft actuators were fashioned in liquid crystalline networks by using a novel tapered film geometry.

Contactless Control of Local Surface Buckling in Photoaligned Gold/Liquid Crystal Polymer Bilayers

Wrinkling is a powerful technique for the preparation of surface structures over large areas, but it is difficult to simultaneously control the direction, period, and amplitude of the wrinkles without resorting to complicated procedures. In this work, we demonstrate a wrinkling system consisting of a liquid crystal polymer network and a thin layer of gold, in which the direction of the wrinkles is controlled by the alignment of the liquid crystal molecules and the average amplitude and period are controlled by a high-intensity UV irradiation. The UV exposure represses the amplitude and period dictated by the total exposure. Using photoalignment and photomasks, we demonstrate an unprecedented control over the wrinkling parameters and were able to generate some striking optical patterns. The mechanism of the wrinkle suppression was investigated and appears to involve localized photodegradation at the polymer-gold interface, possibly due to the formation of mechanoradicals.

Dual electrically and thermally responsive broadband reflectors based on polymer network stabilized chiral nematic liquid crystals: the role of crosslink density

A broadband reflector based on a polymer stabilized chiral nematic liquid crystal has been fabricated. The reflection bandwidth can be manually controlled by an electric field and autonomously by temperature.

Temperature-Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix

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.

Scale-up of a Luminescent Solar Concentrator-Based Photomicroreactor via Numbering-up

The use of solar energy to power chemical reactions is a long-standing dream of the chemical community. Recently, visible-light-mediated photoredox catalysis has been recognized as the ideal catalytic transformation to convert solar energy into chemical bonds. However, scaling photochemical transformations has been extremely challenging due to Bouguer-Lambert-Beer law. Recently, we have pioneered the development of luminescent solar concentrator photomicroreactors (LSC-PMs), which display an excellent energy efficiency. These devices harvest solar energy, convert the broad solar energy spectrum to a narrow-wavelength region, and subsequently waveguide the re-emitted photons to the reaction channels. Herein, we report on the scalability of such LSC-PMs via a numbering-up strategy. Paramount in our work was the use of molds that were fabricated via 3D printing. This allowed us to rapidly produce many different prototypes and to optimize experimentally key design aspects in a time-efficient fashion. Reactors up to 32 parallel channels have been fabricated that display an excellent flow distribution using a bifurcated flow distributor (standard deviations below 10%). This excellent flow distribution was crucial to scale up a model reaction efficiently, displaying yields comparable to those obtained in a single-channel device. We also found that interchannel spacing is an important and unique design parameter for numbered-up LSC-PMs, which influences greatly the photon flux experienced within the reaction channels.

Every photon counts: understanding and optimizing photon paths in luminescent solar concentrator-based photomicroreactors (LSC-PMs)

Monte Carlo simulation of Luminescent Solar Concentrator-based Photomicroreactors (LSC-PM) shows how embedding an absorber (i.e. the reaction channels) within the lightguide can significantly improve the energy efficiency of traditional LSCs on large scale applications.