Nanosized Shape‐Changing Colloids from Liquid Crystalline Elastomers

Haseloh, Sönke; Ohm, C. C.; Smallwood, Fay; Zentel, Rudolf

doi:10.1002/marc.201000324

Cited by 31 publications

(27 citation statements)

References 19 publications

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“…Recently, there has been a growing interest in the fabrication of LCE actuators on a micrometer scale (e.g., for MEMS applications). Examples are pillars on a surface that can change their height,16–18 cantilevers that can bend upon UV irradiation,19 and particles with the ability to change from a spherical to a rodlike shape 14, 20, 21. Herein, we present a method to prepare structurally defined and oriented objects from LCEs that can deform reversibly during a liquid‐crystalline phase transition on a nanometer scale.…”

Section: Methodsmentioning

confidence: 99%

Template‐Based Fabrication of Nanometer‐Scaled Actuators from Liquid‐Crystalline Elastomers

Ohm

Haberkorn

Théato

et al. 2010

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Microelectromechanical systems (MEMS) have recently found strong interest in academia and industry. They result from the integration of mechanical elements, sensors, actuators, and electronics onto a silicon substrate. [ 1 ] The miniaturization of integrated systems offers the advantage of high effi ciency at low fabrication costs and novel functionalities. This emerging technology has led to a strong demand for micro-and nanometerscaled actuators. [ 2 ] Liquid-crystalline elastomers (LCEs) [3][4][5][6] are a class of functional materials that have been used for the fabrication of actuators for many years. Consisting of weakly crosslinked polymer chains that are covalently linked to stiff, shape-anisotropic molecules (mesogens), they combine the ability of self-organization from liquid crystals with the entropy elasticity of elastomers. Depending on the ambient conditions, these mesogens can either be in an unordered state (isotropic phase) or self-organized into ordered liquidcrystalline phases. In the isotropic phase, the polymer chains can adopt the entropically favored random-coil conformation. On the other hand, if the mesogens align into a liquid-crystalline phase, the polymer chains have to respond to the resulting anisotropic environment and adapt an anisotropic conformation. A phase transition between the liquid-crystalline and isotropic phases thus allows switching of the polymer backbone between these two conformations. This conformational change comes along with a macroscopic change of the sample's dimensions, [ 7 ] which enables the utilization of LCEs as materials for actuator applications. [ 6 , 8 , 9 ] Every stimulus that leads to a phase transition in the liquid-crystalline material (heat, UV light, presence of a solvent) can be used to trigger the actuation process. As a result of the reversibility of liquid-crystalline phase transitions, the change in shape is reversible as well. It has to be mentioned that these shape-changing effects can only be

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Section: Methodsmentioning

confidence: 99%

Template‐Based Fabrication of Nanometer‐Scaled Actuators from Liquid‐Crystalline Elastomers

Ohm

Haberkorn

Théato

et al. 2010

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“…Mechanically active polymers1–8 and polymer composites9–15 have attracted tremendous interest as thermosensitive materials because they are able to perform single,16, 17 dual,6, 10, 15, 18–20 or multiple21–24 shape changes at predefined response temperatures ( T sw ). In such polymer systems, T sw is correlated to a thermal transition of the switching domains ( T trans ), which is typically varied by adjusting the polymer's molecular structure (e.g., change in the switching segment length or chemical composition), and requires synthesis of a new material 17, 25–27.…”

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confidence: 99%

Temperature‐Memory Polymer Networks with Crystallizable Controlling Units

et al. 2011

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The switching temperature, Tsw, which must be exceeded to initialize a shape‐memory effect (SME), and Tσ,max, a temperature related to the recovery stress maximum under constant strain‐activation conditions, are adjusted systematically over a wide temperature range for temperature‐memory polymers. The polymers are based on crosslinked poly[ethylene‐ran‐(vinyl acetate)] with crystallizable controlling units and exhibit a broad melting temperature range.

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“…[112,113,128] Oberflächen-Wechselwirkungen konnten auch zur Herstellung von Nanoaktuatoren aus einem Hauptkettenpolyester über einen Miniemulsionsprozess verwendet werden. [129] Die starren Kerne der Mesogene, die Benzolringe, erzeugen Diamagnetismus und kçnnen somit in einem Magnetfeld ausgerichtet werden. [120,130] Keller und Mitarbeiter nutzten diese Eigenschaft, um aktuierende LCE-Mikrosäulen in einem Magnetfeld mit einem Soft-Molding-Verfahren zu synthetisieren (Abbildung 10 B).…”

Section: Herstellung Von Lces Und Ihre Verwendung Als Aktive Bauteileunclassified

Flüssigkristalline Ordnung als Konzept in den Materialwissenschaften: von Halbleitern zu funktionalen Bauteilen

Fleischmann

Zentel

2013

Angewandte Chemie

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Die einzigartigen optischen Eigenschaften von flüssigkristallinen Phasen (LCs) werden schon seit langem in Flachbildschirmen genutzt. Durch die Besonderheiten dieser Mesophase im Zwischenbereich zwischen dem Kristall (Ordnung) und der isotropen Schmelze (Beweglichkeit) eignen sich flüssigkristalline Materialien aber auch zu einer Vielzahl von weiteren Anwendungen. Der hohe Grad an molekularer Ordnung, die Möglichkeit zur großflächigen Orientierung und das Strukturmotiv aromatischer Einheiten machen Flüssigkristalle zu interessanten Materialien für organische Halbleiter, die in Lösungsmitteln verarbeitet und leicht auf Substraten abgeschieden werden können. Die Anisotropie der Flüssigkristalle kann weiterhin zu einer stimuliresponsiven makroskopischen Formänderung von Polymernetzwerken führen, die als reversibel kontrahierende künstliche Muskeln fungieren. Nach Vorstellung des Konzepts der flüssigkristallinen Ordnung beschäftigt sich dieser Aufsatz schwerpunktmäßig mit Strategien zur Synthese neuer Klassen von LC‐Materialien sowie dem Design und der Herstellung aktiver Bauelemente.

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Nanosized Shape‐Changing Colloids from Liquid Crystalline Elastomers

Cited by 31 publications

References 19 publications

Template‐Based Fabrication of Nanometer‐Scaled Actuators from Liquid‐Crystalline Elastomers

Template‐Based Fabrication of Nanometer‐Scaled Actuators from Liquid‐Crystalline Elastomers

Temperature‐Memory Polymer Networks with Crystallizable Controlling Units

Flüssigkristalline Ordnung als Konzept in den Materialwissenschaften: von Halbleitern zu funktionalen Bauteilen

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