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 ...

Monolithically ordered liquid crystal polymer networks are formed by the photoinitiated polymerization of multifunctional liquid crystal monomers. This paper describes the relevant principles and methods, the basic structure− property relationships in terms of mesogenic properties of the monomers, and the mechanical and optical properties of the polymers. Strategies are discussed to control the molecular orientation by various means and in all three dimensions. The versatility of the process is demonstrated by two examples of films with a patterned molecular order. It is shown that patterned retarders can be made by a two-step polymerization process which is successfully employed in a transflective display principle. A transflective display is a liquid crystal display that operates in both a reflective mode using ambient light and a transmissive mode with light coming from a backlight system. Furthermore, a method is discussed to create a patterned film in a single polymerization process. This film has alternating planar chiral nematic areas next to perpendicularly oriented (so-called homeotropic) areas. When applied as a coating to a substrate, the film changes its surface texture. During exposure to UV light, it switches from a flat to a corrugated state.

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Coatings with a dynamic surface topography are of interest for applications in haptics, soft robotics, cell growth in biology, hydro- and air dynamics and tribology. Here we propose a design for creating oscillating surface topographies in thin liquid crystal polymer network coatings under an electric field. By applying an alternating electric field, the coating surface deforms, and pre-designed local corrugations appear. The continuous AC electric field further initiates oscillations superimposed on the formed topographies. This effect is based on microscopic free volume creation. By exciting the liquid crystal network at its resonance frequency, maximum free volume is generated and large surface topographies are formed. Molecular simulation is used to examine this behaviour in microscopic detail as a function of oscillation frequency. Surface topography formation is fast and reversible. Excess free volume is energetically unfavourable, thus the surface topographies disappear within seconds once the electric field is removed.

Photoactivated generation of disorder in a liquid crystal network produces free volume that leads to the controlled formation of dynamic corrugations at its surface. The liquid crystal order amplifies the deformation of copolymerized azobenzene, which takes place on molecular length scales, to a micrometre-sized macroscopic phenomenon based on changes in density. We postulate a new mechanism in which continuous oscillating dynamics of the trans-to-cis isomerization of the azobenzene overrules the net conversion, which is currently considered as the origin. This is supported by a significant local density decrease when both the trans and cis isomers are triggered simultaneously, either by dual-wavelength excitation or by the addition of a fluorescent agent converting part of the light to the cis-actuating wavelengths. This new insight provides a general guideline to boost free volume generation leading not only to larger macroscopic deformations but also to controllable and faster non-equilibrium dynamics.