This review collects recent developments in the field of liquid crystalline elastomers (LCEs) with an emphasis on their use for actuator and sensor applications. Several synthetic pathways leading to ...crosslinked liquid crystalline polymers are discussed and how these materials can be oriented into liquid crystalline monodomains are described. By comparing the actuating properties of different systems, general structure–property relationships for LCEs are obtained. In the final section, how these materials can be turned into usable devices using different interdisciplinary techniques are described.
Monodomains of liquid crystalline elastomers (LCEs) show a reversible shape change during the phase transition from the liquid crystalline to isotropic phase. Different synthetic pathways leading to oriented LCE samples are reviewed before discussing their actuating properties in terms of their chemical structure. In addition, the construction of devices, based on these fascinating materials, are presented.
Despite decades of attempts to reveal its flaws, the Standard Model of particle physics (SM) has withstood all experimental tests and its predictions are in excellent agreement with data. Since the ...theory was formulated, experiments have provided little guidance regarding the explanations of phenomena not described by the SM, such as the baryon asymmetry of the universe and dark matter. Nor do we have satisfying understanding of the aesthetic and theoretical problems of the model, despite years of searching for new processes and particles proposed to solve them. Such particles can evade being discovered by the comprehensive search programs at collider experiments if the analysis selections and the algorithms used to reconstruct the detector data are not matched to the characteristics of the particles, e.g. if they have long enough lifetimes. As interest in searches for such long-lived particles at colliders grows rapidly, we present a review of this area of research in this article. The broad range of theoretical motivations for particles with long lifetimes and the experimental strategies and methods employed to search for them are described. Results from decades of searches are reviewed, as are opportunities for the next generation of searches both at existing and proposed future experiments.
We demonstrate the use of a microfluidic setup to prepare monodisperse and spherical beads from a liquid crystalline elastomer. These particles show a strong and reversible shape change into a ...cigar‐like conformation during the transition into the isotropic phase. These properies are a result of the monodomainic alignment of the mesogens in the flow field of the microfluidic setup.
Nanowires are prepared from liquid‐crystalline elastomers by the use of anodized aluminum oxide as a template. The obtained rodlike structures are monodisperse and possess a uniform alignment. They ...show reversible actuation—a change in length of roughly 40%—during phase transition from the nematic to the isotropic phase.
In this article new results on the preparation of monodisperse particles from a liquid crystalline elastomer in a microfluidic setup are presnted. For this, droplets from a liquid crystalline monomer ...are prepared in a microfluidic device and polymerized while they are flowing inside a microtube. The particles obtained by this method possess an internal orientation, which gives them actuating properties. When they are heated into the isotropic phase of the liquid crystalline material they show a reversible change in shape whereby they change their length in one direction by almost 100%. It is shown how the variation of experimental parameters during their synthesis impacts the properties of these micro‐actuators. Influence over their primal shape, the strength of their shape changing properties, their size, and their mechanical properties is demontrated. From the systematic variation of experimental parameters a deep understanding of the complex processes taking place in a flowing droplet of a liquid crystalline material is obtainted. Additionally NMR analysis and swelling experiments on these actuating materials are provided.
The use of a microfluidic setup to prepare monodisperse particles from a liquid crystalline elastomer is presented. After the application of a stimulus like heat or the presence of a solvent these show a strong and reversible shape change. The possibility to control the particle actuational behavior, shape, size, and mechanical properties is demonstrated.
Using in situ transmission electron microscopy, we find that a carbon shell governs the morphological transitions of gold and silver nanorods upon heating. Encapsulated Ag nanorods show a surprising ...nonuniform sublimation behavior starting from one side and leaving behind the shell. Uncovered gold nanorods transform their shape to spheres well below the bulk melting temperature through surface diffusion, which is prevented by a thin carbon shell.
We present the synthesis of a polymeric liquid crystalline (LC) crosslinker and its usage in the preparation of soft microactuators. The microactuators, composed of thermoresponsive liquid ...crystalline elastomers (LCE), are fabricated in a microfluidic device in a continuous “on the fly” process. The LC polymer crosslinker is miscible with the LC monomer and provides for a rapid polymerization and crosslinking. Most importantly, it promotes an enantiotropic mesophase of the mobile monomer phase, which is not provided by conventional nonmesogenic crosslinkers. This allows an isothermal handling inside the microfluidic setup. Temperature‐driven shape changes up to 65% could be achieved by judiciously optimizing the crosslinking density of the LCE particles.
Synthesis of a liquid‐crystalline polymer crosslinker designed for the preparation of liquid crystalline elastomers (LCE) and its application inside a microfluidic device. The resulting thermoresponsive microactuators show a reversible shape change upon the nematic‐isotropic phase transition.
A microfluidic setup was used to process lyotropic cholesteric liquid crystalline mixtures of cellulose derivatives into spherical particles in the micrometre scale. By the method of co-flowing ...injection, monodisperse droplets of the liquid crystal, dispersed in an aqueous carrier fluid, were prepared. Polymerization of the acrylic solvent with UV-light fixed the orientation obtained by the flowing motion. The resulting particles were characterized by polarizing optical microscopy.
Micrometre-sized particles of cellulose derivatives showing a cholesteric liquid crystalline phase were prepared in a microfluidic setup by co-flowing injection.
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