Name: orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets
Uploaded: 2017-05-15T13:00:00.000+00:00
Duration: 6 min 26 s
Description: Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Este trabalho foi apoiado por JSPS KAKENHI concessão número 16H06037. Agradecemos sinceramente ao Dr. Yuji Sasaki na Universidade de Hokkaido pela assistência técnica para HR-DSC.

1. Preparação da camada de alinhamento de cristais líquidos de um perfluoropolímero sobre substratos de vidro <ol><li> Preparação da solução de perfluoropolímero <ol><li> Preparar 1 mL da solução de perfluoropolímero por dissolução de uma solução de perfluoropolímero (9% em peso de polímero) num solvente comercial numa proporção de 1: 2; Isto assegura filmes uniformes de 0,5-1 um de espessura para serem revestidos por centrifugação. NOTA: Consulte a lista de materiais para a solução eo solvente utilizados. </li></ol></li><li> Revestimento do perfluoropolímero em substratos de vidro limpos <ol><li> Lavar os substratos de vidro (tamanho típico: 1 cm x 1 cm) por sonicação a 38 ou 42 kHz num detergente alcalino. Lavar repetidamente com água destilada. Tipicamente, enxágüe mais de 10 vezes, com 5 minutos de sonicação cada vez. </li><li> Sujeitar os substratos ao aspirador UV-O 3 durante 10 min. </li><li> Gotejar 20 μL da solução do passo 1.1 para o substracto de vidro limpoTes Imediatamente centrifugar a solução a 3.500 rpm e à temperatura ambiente durante 70 s. Asse o filme a 80 ° C durante 60 min para remover o solvente e a 200 ° C durante 60 min para a cura. </li></ol></li></ol> 2. Preparação de células LC <ol><li> Colar dois substratos de vidro revestidos com película juntos usando uma resina foto-curável e uma lâmpada LED com um comprimento de onda de 365 nm (1,1 W / cm 2 ). Ajustar a espessura do intervalo entre os dois substratos para dentro da gama de 2-100 μm utilizando partículas de vidro de tamanho micrométrico ou películas de naftalato de polietileno. </li><li> Introduzir um material LC 4&#39;-butil-4-heptil-biciclo-hexil-4-carbonitrilo (CCN47; 0,2-10 μL) 9 nas células LC preparadas utilizando uma espátula sob força capilar a uma temperatura superior à do líquido isotrópico (I) -nematica (N) temperatura de transio de fase. NOTA: CCN47 tem uma anisotropia dieléctrica negativa, ea sequência de fases é Cry 298,6 K SmA 301,3 KN 331,3 KI, onde Cry e SmA representam fases cristalinas e smecticas. Não introduza CCN47 na fase N ou fase SmA, porque o alinhamento induzido por fluxo seria promovido. </li></ol> 3. Caracterização da Amostra <ol><li> Observação de textura por microscopia óptica polarizante (POM) 10 <ol><li> Observe as células LC sob POM com lentes objetivas 4-100X em conjunto com um estágio quente para controlar a temperatura da amostra com precisão de ± 0,1-K. Registre as texturas em mais de 5 quadros, em intervalos regulares por Kelvin. Use uma câmera colorida digital sequencialmente, tanto após o resfriamento e aquecimento na faixa de 291-343 K. </li></ol></li><li> Espectroscopia dielétrica (DS) 11 <ol><li> Prepare células LC, com eletrodos ITO - que podem ter uma forma quadrada ou circular e podem ser adquiridos comercialmente - em ambos os substratos. Soldar um fio condutor a cada substrato. NOTA: Consulte a lista de materiais para os substratos utilizados. </li><li> Medir a capacitância ou constante dielétrica das células LC, exatamente como usado para POM, usando um analisador de impedância comercial / fase de ganho. Assegurar que o estado das amostras é equilibrado antes de cada medição. Meça a dependência do tempo da capacitância ou da constante dielétrica das células LC medindo a capacitância das células LC manualmente a cada 5 min. </li><li> Inicie a medição DS somente se a capacitância ou a constante dielétrica das células LC se tornarem não dependentes do tempo. </li></ol></li><li> Calorimetria de varredura diferencial de alta resolução (HR-DSC) 12 <ol><li> Coloque as células LC em um HR-DSC caseiro para ser examinado, exatamente como no POM ( nunca use panelas DSC). Consulte a Referência 12 para projetar e construir um HR-DSC e aprender a usá-lo. Realizar medições com taxas de varredura de 0,05-0,10 K / min para aumentar a temperatura mínima de resolução powEr </li></ol></li><li> Difracção de raios X de incidência de pastejo (GI-XRD) 13 <ol><li> Colocar a célula LC (utilizada para POM ou DSC) ou uma amostra com uma gotícula de 2 a 5 μL de CCN47 sobre um substrato revestido na fase de amostra GI-XRD, que deve ser equipada com um controlador de temperatura. </li><li> Equilibrar a amostra durante mais de 10 min a temperaturas desejadas na gama de 291-343 K, ambos por arrefecimento e aquecimento. </li><li> Use um feixe de raio X incidente na amostra, com um ângulo de incidência de minutos em torno de 0,05-0,10 °, para extrair informações de superfície sobre orientação molecular e ordens / estruturas. Swing o ângulo de incidência do feixe de raios X para encontrar o ângulo de incidência ideal em que a força da difração é o mais forte. Faça as medições no ângulo de incidência ótimo. NOTA: Tenha em mente que o GI-XRD torna possível detectar as peculiaridades interfaciais na escala nanométrica, maximizando assim o sinal deEnquanto minimiza o sinal do volume. Observe que as geometrias XRD normais, além de GI-XRD, não são métodos sensíveis à superfície, uma vez que o raio X tem uma grande profundidade de penetração em materiais. </li></ol></li></ol>

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As 10x imagens POM tiradas utilizando uma célula LC de 5 μm ( Figuras 1a e b ) mostram claramente que o estado de orientação das moléculas LC a granel transita entre as orientações P e V à variação de temperatura de uma maneira de primeira ordem. Isto é marcado pelos processos de nucleação e crescimento do domínio, com uma nova orientação diferindo da orientação inicial em 90 °. As temperaturas de transição após arrefecimento e aquecimento são 321,5 K e 325,3 K, r...

Nos últimos anos tem havido um interesse crescente em aprender como as características moleculares dinâmicas e as estruturas das moléculas de superfície em resposta a estímulos externos podem afetar a orientação em massa de materiais em estados LC. Um exemplo é usar biossensores LC como uma nova aplicação das LCs 1 , 2 . Para quantificar quantas espécies-alvo são detectadas, é importante saber como as LCs interfaciais que entram em contato com as moléculas alvo aderentes mudam e evoluem, enquanto também detectam e como elas transferem / traduzem suas propriedades para o volume. Usando modelos para perseguir essas respostas, começamos com sistemas que têm sua orientação molecular de superfície e ordens de curto alcance variando termodinamicamente. Estes sistemas permitem correlacionar as mudanças na orientação superficial e ordens com a orientação granel resultante de uma maneira sistemática. Recentemente, encontramos vários sistemas LC que exibemTransições rientacionais, onde uma orientação de massa molecular espontânea muda com a temperatura. Em princípio, as transições orientacionais podem ser categorizadas em transições de quase-segunda ordem 3 , 4 ou quase-primeira-ordem 5 , 6 , 7 , 8 . O primeiro é acompanhado por uma reorientação molecular contínua em massa sobre as mudanças de temperatura, enquanto que o último demonstra uma reutilização descontínua. Neste artigo, descrevemos uma transição orientacional na forma de quase-primeira ordem entre os estados orientativos P e V. Prossegue na fase nematic única (N) mudando a temperatura. Os detalhes serão fornecidos nos Resultados Representativos e na Discussão. Como a mudança de orientação na massa deve ser governada por uma mudança na orientação molecular da superfície e, É evidente que este sistema pode potencialmente oferecer insights sobre como a variação termodinâmica na orientação molecular de superfície e ordens de curto alcance afeta a orientação em massa. Neste artigo, com o objetivo de compreender as questões acima mencionadas, abordamos três problemas usando quatro métodos complementares ( ie, POM, DS, HR-DSC e GI-XRD): (1) Como é a transição orientacional? (2) A transição orientacional é termicamente detectável? (3) Por que e como ocorre a transição orientacional?

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orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets

Na química física do cristal líquido (LC), as moléculas perto da superfície desempenham um grande papel no controle da orientação volumétrica. Até agora, principalmente para alcançar os estados de orientação molecular desejados em monitores LC, a propriedade de superfície &quot;estática&quot; de LCs, a chamada ancoragem superficial, tem sido intensamente estudada. Como regra geral, uma vez que a orientação inicial das LCs é &quot;bloqueada&quot; por tratamentos de superfície específicos, tais como a fricção ou o tratamento com uma camada de alinhamento específica, dificilmente muda com a temperatura. Aqui, apresentamos um sistema exibindo uma transição orientacional sobre a variação de temperatura, o que entra em conflito com o consenso. Logo na transição, as moléculas LC em massa experimentam a rotação orientativa, com 90 ° entre a orientação planar (P) a altas temperaturas e a orientação vertical (V) a baixas temperaturas na transição de primeira ordem. Nós seguimos o comportamento de ancoragem da superfície termodinâmica por meio da microscopia óptica polarizadora (POM), espectroscopia dielétrica (DS), calorimetria de varredura diferencial de alta resolução (HR-DSC) e difração de raios X de incidência de pasto (GI-XRD) e atingiu uma explicação física plausível: a transição é desencadeada por um crescimento de superfície Que impõem a orientação V localmente contra a orientação P na massa. Essa paisagem forneceria uma ligação geral explicando como a orientação em massa de equilíbrio é afetada pela orientação localizada na superfície em muitos sistemas LC. Em nossa caracterização, POM e DS são vantajosos oferecendo informações sobre a distribuição espacial da orientação das moléculas LC. HR-DSC fornece informações sobre as informações termodinâmicas precisas sobre transições, que não podem ser tratadas por instrumentos DSC convencionais devido à resolução limitada. GI-XRD fornece informações sobre orientação molecular específica de superfície e ordenações de curto alcance. O objetivo deste trabalho é apresentar um protocolo para a preparação de uma amostra que exiba o transiE demonstrar como a variação estrutural termodinâmica, tanto no volume quanto nas superfícies, pode ser analisada pelos métodos acima mencionados.

As imagens de POM, dados DS, dados HR-DSC e padrões GI-XRD foram recolhidos durante a variação de temperatura, especialmente na vizinhança da transição de orientação tanto ao arrefecimento como ao aquecimento. A Figura 1 representa a evolução da textura feita pelas medições de POM e DS durante a observação de POM da transição de orientação do estado de orientação P (V) para V (...

Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Aqui, apresentamos um protocolo para desencadear uma transição de orientação de um cristal líquido em resposta à temperatura. São descritas metodologias para a preparação de uma amostra, a fim de observar a transição ea evolução de transição detalhada.

Transição Orientacional em Cristal Líquido Ativada pelo Crescimento Termodinâmico de Folhas Múltiplas Interfaciais

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

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7.1K visualizações.  RIKEN Center for Emergent Matter Science (CEMS).  Aqui, apresentamos um protocolo para desencadear uma transição de orientação de um cristal líquido em resposta à temperatura. São descritas metodologias para a preparação de uma amostra, a fim de observar a transição ea evolução de transição detalhada. 

Vídeo: Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

Oxidação seca e vácuo Annealing Tratamentos para Ajustando as propriedades de umectação Matrizes Nanotubos de Carbono

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

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Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.

A growing number of radiation therapy devices offer the advantage of delivering the dose through very small beams to the tumor, allowing for increased conformity and higher doses per fraction. Many different detectors can be used for the dosimetry of these small fields. In the present study, the effect of ion recombination is investigated for a liquid ionization chamber using a stereotactic radiation therapy system.

Caracterização dos Efeitos de recombinação em uma Câmara de ionização líquido usado para a dosimetria de um Acelerador Radiosurgical

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via ...

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 &#181;l/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods.

Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

Fase Diagrama Caracterização utilizando esferas magnéticas como veículos líquidos

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Síntese e esfoliação da discotic Zircônio Fosfatos obter cristais coloidais líquidos

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

Química

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

Preparação das redes de cristal líquido para macroscópica movimento oscilatório induzido pela luz

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

Novas técnicas para observar a dinâmica estrutural de cristais líquidos de Photoresponsive

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

Microfluidic preparação dos atuadores do líquido cristalino de elastômero

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Medir a polarização ferroelétrica magneticamente sintonizado em cristais líquidos

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

Preparação de Monodomain cristal líquido elastômeros e de cristal líquido Elastomer nanocompósitos

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

Bioengenharia

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Troca fotorologia de alto contraste e rápida de um cristal líquido nematic de curvatura

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...