Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates

<p><b>In nature, proteins like rhodopsin act as transducer for photo-chemical reactions causing biological responses (e.g. enabling vision)</b><b>. The underlying concept – a photo-induced conformational change of the protein as amplifier of the photo-responsive moiety – can also be adopted by synthetical polymers or foldamers</b><b> </b><b>that have the propensity to form ordered secondary structures (e.g. polypeptides)</b><b>. An alternative approach to amplify photo-chemical responses is their incorporation into liquid crystals</b><b>. With only a few exceptions</b><b>, photo-insensitive liquid crystals are doped with dyes</b><b> </b><b>that favour disorder upon irradiation</b><b>. In theory, photo-responsive polypeptides</b><b>, capable of forming lyotropic liquid crystals</b><b>, could exploit both amplification approaches but, in practice, their photo-responsivity is hampered by the reduced mobility of polypeptides in concentrated solutions</b><b>. Here we show that the E/Z photo-isomerisation of an azobenzene containing polyaspartate initiates a helix-coil backbone transition, which reversibly alters the polypeptide solution from anisotropic to isotropic. In contrast to other photo-responsible polymers</b><b>14</b><b>, in which thermal relaxation to the more stable photo-isomer is quite fast, both photo-isomers are thermally stable and interconvertible by visible light in a single solvent. Local irradiation and magnetic fields lead to spatial resolution and unidirectional architectures of the liquid crystal, respectively. Our results demonstrate that photo-isomerisation on a molecular level is amplified in three stages via intra- and intermolecular interactions to yield a unidirectional, chiral liquid crystal. We believe, the morphological changes of the liquid crystal induced by light will facilitate a multitude of applications, like photo-alignment</b><b> </b><b>or the photo-control of solution viscosity</b><b> </b><b>and anisotropic </b><br></p> <p><b>diffusion</b><b>. When incorporated into layer-by-layer architectures the polymer could find application in biomedicine</b><b> </b><b>and the spatial and temporal resolution could be exploited in nano-technology</b><b>. </b></p>

Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates

<p><b>In nature, proteins like rhodopsin act as transducer for photo-chemical reactions causing biological responses (e.g. enabling vision)</b><b>. The underlying concept – a photo-induced conformational change of the protein as amplifier of the photo-responsive moiety – can also be adopted by synthetical polymers or foldamers</b><b> </b><b>that have the propensity to form ordered secondary structures (e.g. polypeptides)</b><b>. An alternative approach to amplify photo-chemical responses is their incorporation into liquid crystals</b><b>. With only a few exceptions</b><b>, photo-insensitive liquid crystals are doped with dyes</b><b> </b><b>that favour disorder upon irradiation</b><b>. In theory, photo-responsive polypeptides</b><b>, capable of forming lyotropic liquid crystals</b><b>, could exploit both amplification approaches but, in practice, their photo-responsivity is hampered by the reduced mobility of polypeptides in concentrated solutions</b><b>. Here we show that the E/Z photo-isomerisation of an azobenzene containing polyaspartate initiates a helix-coil backbone transition, which reversibly alters the polypeptide solution from anisotropic to isotropic. In contrast to other photo-responsible polymers</b><b>14</b><b>, in which thermal relaxation to the more stable photo-isomer is quite fast, both photo-isomers are thermally stable and interconvertible by visible light in a single solvent. Local irradiation and magnetic fields lead to spatial resolution and unidirectional architectures of the liquid crystal, respectively. Our results demonstrate that photo-isomerisation on a molecular level is amplified in three stages via intra- and intermolecular interactions to yield a unidirectional, chiral liquid crystal. We believe, the morphological changes of the liquid crystal induced by light will facilitate a multitude of applications, like photo-alignment</b><b> </b><b>or the photo-control of solution viscosity</b><b> </b><b>and anisotropic </b><br></p> <p><b>diffusion</b><b>. When incorporated into layer-by-layer architectures the polymer could find application in biomedicine</b><b> </b><b>and the spatial and temporal resolution could be exploited in nano-technology</b><b>. </b></p>

DIGITALIZACIÓN DE FORMAS DE LA NATURALEZA COMO RECURSO MORFOLÓGICO

La biomimética imita los procesos naturales para plantear posibles soluciones a problemas humanos y ha sido aplicado por varias profesiones, convirtiéndose en una práctica recurrente para adoptar nuevas morfologías o principios funcionales. Leonardo de Pisa empleó estos fenómenos y desarrolló una serie matemática llamada sucesión de Fibonacci, dando lugar posteriormente a la proporción áurea. Estos descubrimientos matemáticos se manifiestan en forma concurrente en patrones geométricos de los procesos y estructuras de la naturaleza como en la distribución de hojas en las plantas. El objetivo de este artículo es proponer recursos formales procedentes de la aplicación de la biomimética de manera superficial/reductiva, que adopta la morfología de la planta Sempervivum tectorum L. para futuras soluciones formales y funcionales del ámbito del diseño. Para ello, se aplica la fotogrametría como técnica para capturar información bidimensional mediante fotografías y convertirlas en información tridimensional, obteniendo un modelo idéntico al original. La digitalización del elemento natural cumple con la siguiente metodología: preparación del entorno, toma de datos, alineación de fotografías, creación de nube de puntos densa, creación de malla y la textura. Posteriormente se realiza la construcción de modelos 3D, siguiendo el recorrido helicoidal digitalizado. Esta trayectoria crea un patrón en forma de hélice que se repite en sentido radial, tomando como referencia el eje vertical, de esta manera se crea un vórtice en la corona del sólido. A partir de esta estructura se realiza variaciones morfológicas, respetando la dirección de la hélice matriz. Palabras clave: Morfología, fotogrametría, ángulo de oro, sucesión de Fibonacci, diseño. AbstractBiomimetics mimics natural processes to propose possible solutions to human problems and has been applied by various professions, making it a recurring practice to adopt new morphologies or functional principles. Leonardo of Pisa used these phenomena and developed a mathematical series called the Fibonacci sequence, later giving rise to the golden ratio. These mathematical discoveries are manifested concurrently in geometric patterns of the processes and structures of nature as in the distribution of leaves in plants. The objective of this article was to propose formal resources from the application of biomimetics in a superficial / reductive way, which adopts the morphology of the Sempervivum tectorum L. plant for future formal and functional solutions in the field of design. To this end, photogrammetry was applied as a technique to capture two-dimensional information through photographs and convert them into three-dimensional information, obtaining a model identical to the original. The digitization of the natural element complied with the following methodology: environment preparation, data collection, photo alignment, dense point cloud creation, mesh and texture creation. Subsequently, the construction of 3D models is carried out, following the digitized helical path. This path created a helix-shaped pattern that was repeated radially, taking the vertical axis as a reference, thus creating a vortex in the crown of the solid. Morphological variations were made from this structure, respecting the direction of the parent helix. Keywords: Morphology, digital photogrammetry, golden angle, Fibonacci sequence, design.

A Planar Fresnel Lens in Reflection Type Based on Azo-Dye-Doped Cholesteric Liquid Crystals Fabricated by Photo-Alignment

This paper presents a focusing efficiency and focal length tunable planar Fresnel lens in reflection type based on azo-dye-doped cholesterol liquid crystal film. The Fresnel-like pattern of a pumping beam can be formed by a Sagnac interferometer. When the azo-dye molecules are irradiated by the pumping beam, the photoalignment effect will be induced in the bright (odd) zones due to the trans–cis photoisomerization of azo-dye molecules. Thus, the structures of cholesteric liquid crystals in the odd zones will reorient from the imperfectly planar textures to the perfectly planar textures. The different structures of cholesteric liquid crystals in two adjacent zones will give rise to phase difference for the reflected light and thus function as a Fresnel lens. The focusing efficiency of the proposed Fresnel lens can be controlled by the applied voltages and affected by the polarization state of incident light. Moreover, various focal lengths of the Fresnel lens can be achieved by rewriting a different center radius of the Fresnel-like pattern.

Capillary Flows of Nematic Liquid Crystal

In this paper we report the new experimental results on the rise of a liquid crystal in flat capillaries with inner photosensitive surfaces. The capillaries with different surface orientations were prepared by the use of the photo-alignment technique. Such a surface treatment makes it possible to eliminate the noncontrollable influence of a nanorelief on the wetting process, which takes place in the rubbing treatment technique previously used in similar experiments. The dynamics of the capillary rise of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl) in vertical plane capillaries with photo-aligned substrates were studied for the first time. It was found that the stationary value of a contact angle weakly depends on the direction of a planar surface orientation relative to the direction of a capillary rise. It has been shown that the application of strong electric fields resulted in a decreasing of the contact angle. The results, obtained for the nematic liquid crystal, are compared with the results of an investigation of the capillary flow in a shock-free ferroelectric smectic phase.

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

Photo-alignment is a versatile tool to pattern the alignment at the confining substrates in a liquid crystal (LC) cell. Arbitrary alignment patterns can be created by using projection with a spatial light modulator (SLM) for the illumination. We demonstrate that a careful design of the alignment patterns allows the stabilization of topological solitons in nematic liquid crystal (NLC) cells, without the need for chirality or strong confinement. The created LC configurations are stabilized by the anchoring conditions imposed at the substrates. The photo-aligned background at both substrates is uniformly planar aligned, and ring-shaped regions with a 180° azimuthal rotation are patterned with an opposite sense of rotation at the top and bottom substrate. A disclination-free structure containing a closed ring of vertically oriented directors is formed when the patterned rings at the top and bottom substrate overlap. Thanks to the topological stability, a vertical director orientation in the bulk is observed even when the centra of both patterned rings are shifted over relatively large distances. The combination of numerical simulations with experimental measurements allows identification of the 3D director configuration in the bulk. A finite element (FE) Q-tensor simulation model is applied to find the equilibrium director configuration and optical simulations are used to confirm the correspondence with experimental microscopy measurements. The created LC configurations offer opportunities in the field of optical devices, light guiding and switching, particle trapping and studies of topological LC structures.