troactive polymers, [7] as well as patterned hydrogels that shape-shift on swelling. [8,9] Further development of soft elements capable to perform complex motions or functions requires adequate materials and processing technologies that enable accurate control of the mechanical response. Moreover, on the route toward practical applications, there is often a necessity to have the possibility to miniaturize these elements, produce them in large dimensions or over large areas, or integrate them with other materials, elements, or devices.Crosslinked liquid crystalline polymers (LCPs) have received much attention as candidates for this purpose since they can exhibit large macroscopic scale mechanical response to different external stimuli such as heat, light, pH, or moisture. [10][11][12] Thinfilms of these materials with controlled molecular orientation, defined by the director (n), have predominantly been investigated as building blocks to implement a variety of responsive elements or devices. [13][14][15][16][17][18][19][20][21][22] However the thinfilm character of these elements markedly limits the energy available for actuation. Even more, the reported systems, including their processing toolbox, are limited to one single material and therefore multifunctional and multiresponsive systems are difficult to create. For the true development and incorporation of these LCP structures in real life applications, the capability to generate elements of different sizes, from very small to very large, is fundamental. This needs to be done with a precise control of the material morphology and properties as well as director orientation in well-defined complex geometries, all together leading to an accurate control of the mechanical response.Additive manufacturing techniques enable digital generation of material patterns in surfaces or fabrication of 3D objects. While 3D printing of conventional materials leads to inanimate 3D objects with static shape, 4D printing of responsive materials adds a 4th dimension as it leads to architectures that, with an appropriate stimulus, change their shape over time. [9,23] Here, we report the 4D printing of liquid crystalline elastomer (LCE) macro-and microstructures. Digital control of the local anisotropy of the applied LC material is advantageously achieved through the printing process. This allows to precisely program the magnitude and directionality of the forces in response to the external stimulus, temperature in our case, and therefore well-defined reversible shape-morphing of the structures in space and time. Although 4D printing has been recently described with hydrogels charged with anisotropic cellulose fibrils that get oriented during printing, [9] the mechanical response of these materials is based on water swelling, which limits the applicability due to the specific and stringent environment required for actuation as well as the slow response 3D Printing Soft matter elements undergoing programed, reversible shape change can contribute to fundamental advance in areas such as ...

Rise or fall: Complex-structured freestanding polymer films with molecular order in three dimensions were prepared through photoalignment of polymerizable liquid crystals. The resulting films deform into cone and saddle shapes upon heating.

This work describes the fabrication, characterization, and modelling of liquid crystalline polymer network films with a multiple patterned 3D nematic director profile, a stimuli‐responsive material that exhibits complex mechanical actuation under change of temperature or pH. These films have a discrete alternating striped or checkerboard director profile in the plane, and a 90‐degree twist through the depth of the film. When actuated via heating, the striped films deform into accordion‐like folds, while the film patterned with a checkerboard microstructure buckles out‐of‐plane. Furthermore, striped films are fabricated so that they also deform into an accordion shaped fold, by a change of pH in an aqueous environment. Three‐dimensional finite element simulations and elasticity analysis provide insight into the dependence of shape evolution on director microstructure and the sample's aspect ratio.

producing increasingly complex patterned films and miniaturized devices, which are required in modern information and communication technologies. [1] In addition to semiconductor device fabrication, a host of applications for patterned thin films and structured polymeric systems have been identified over the last two decades in areas including optics, energy harvesting, biotechnology, and medicine. [2] Our ability to structure polymeric materials has grown tremendously and the palette of materials and techniques to achieve a quick and reliable production of patterns with increasing resolution is quite extensive. This boom has been largely sustained by the development of specific photonic technologies, such as advanced light sources or spatial light modulators, photosensitive materials, and, more importantly, our growing knowledge of the interaction between light and matter. Indeed, the ability to control a chemical reaction with light in a remote fashion is a powerful concept. Light irradiation can initiate a photochemical process that otherwise would not occur at ambient conditions. This property lies at the origin of the temporal control afforded by simply turning the light source on and off. Moreover, patterned illumination or the use of focused light beams enables control of not only when, but also where a photoinduced transformation occurs. The photochemical processes occurring in many polymers and resists can be effectively manipulated by fine-tuning the intensity and frequency of light. However, these are just two of the primary properties of light, and there are specific photoresponsive systems that enable the generation of ordered structures by adjusting the polarization of light, in addition to intensity and frequency.In this review, an overview of photochemical reactions, photosensitive polymers, and light-based structuring techniques is provided. As this field is too broad to be covered in depth in one single article, some recent examples and applications, as well as emerging opportunities and trends, are highlighted throughout the discussion. Section 2 is focused on light-induced reactions and photosensitive materials. The fundamentals of photochemical reactions and their implementation in polymer science have been overviewed in many excellent books and reviews. [3] In Section 2, rather than being comprehensive, emphasis is given to those photochemical processes lying at the basis of those structuring techniques that are later discussed in Section 3. Some of these techniques, including conventional mask lithographies, interference lithographies, direct laser writing (DLW) with one-or two-photon processes, or stereolithographic techniques, make use of light as a structuring tool.There is an additional group of techniques where light is employed to set a structure created beforehand through a Over the last few decades, the demand of polymeric structures with welldefined features of different size, dimension, and functionality has increased from various application areas, including microelectronics, ...

Remote light exposure of photoresponsive liquid crystalline polymers has drawn great attention over the last years as an attractive strategy to generate mechanical work with high spatial resolution. To tailor these materials into practical engineering devices, it is of key importance to gain control over their morphology and thus precisely program their mechanical response, which must also be fast and relevant in magnitude. In this communication, we report the four-dimensional (4D) printing of azobenzene-containing liquid crystalline elastomers (LCEs) that respond to light. During extrusion of the LCE precursor, mesogen orientation is defined by the needle's moving direction enabling a precise definition of the director, which is later fixed by photopolymerization. Fast mechanical responses have been observed in these 4D printed LCE elements when excited with ultraviolet (UV) light. These 4D printed elements lift objects many times heavier than their own weight, demonstrating a capacity to produce effective work. Photochemical and photothermal contributions to the deformation and force have been identified. Advantageously, the use of blue and UV light excitation enables adjustment of generated forces that can be maintained even in the dark and can be released by light excitation or temperature. The demonstrated ability to generate light-responsive elements quickly delivering sufficient work paves the way for implementing remotely addressed mechanical functions to future soft robotics and engineering.

Auf‐ oder abwärts: Komplex strukturierte freistehende Polymerfilme mit einer dreidimensionalen molekularen Ordnung wurden durch Photoausrichtung polymerisierbarer Flüssigkristalle hergestellt. Die gebildeten Filme verformen sich beim Erhitzen zu Kegel‐ und Sattelformen.

Inkjet printing, traditionally used in graphics, has been widely investigated as a valuable tool in the preparation of functional surfaces and devices. This review focuses on the use of inkjet printing technology for the manufacturing of different optical elements and photonic devices. The presented overview mainly surveys work done in the fabrication of micro-optical components such as microlenses, waveguides and integrated lasers; the manufacturing of large area light emitting diodes displays, liquid crystal displays and solar cells; as well as the preparation of liquid crystal and colloidal crystal based photonic devices working as lasers or optical sensors. Special emphasis is placed on reviewing the materials employed as well as in the relevance of inkjet in the manufacturing of the different devices showing in each of the revised technologies, main achievements, applications and challenges.

No abstract