C. Tolksdorf

Giant lateral electrostriction in ferroelectric liquid-crystalline elastomers

Mechanisms for converting electrical energy into mechanical energy are essential for the design of nanoscale transducers, sensors, actuators, motors, pumps, artificial muscles, and medical microrobots. Nanometre-scale actuation has to date been mainly achieved by using the (linear) piezoelectric effect in certain classes of crystals (for example, quartz), and ‘smart’ ceramics such as lead zirconate titanate. But the strains achievable in these materials are small—less than 0.1 per cent—so several alternative materials and approaches have been considered. These include grafted polyglutamates (which have a performance comparable to quartz), silicone elastomers (passive material—the constriction results from the Coulomb attraction of the capacitor electrodes between which the material is sandwiched) and carbon nanotubes (which are slow). High and fast strains of up to 4 per cent within an electric field of 150 MV m-1 have been achieved by electrostriction (this means that the strain is proportional to the square of the applied electric field) in an electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer. Here we report a material that shows a further increase in electrostriction by two orders of magnitude: ultrathin (less than 100 nanometres) ferroelectric liquid-crystalline elastomer films that exhibit 4 per cent strain at only 1.5 MV m-1. This giant electrostriction was obtained by combining the properties of ferroelectric liquid crystals with those of a polymer network. We expect that these results, which can be completely understood on a molecular level, will open new perspectives for applications.

Elastic Properties of Liquid Crystal Elastomer Balloons

Abstract We introduce a method to measure elastic properties of smectic liquid crystalline elastomers. Freely suspended smectic polymer films containing photoreactive groups are inflated to spherical bubbles and crosslinked by UV light irradiation. After crosslinking, the balloon volume is varied and elastic properties of the material are determined from the relation between radius and inner excess pressure. The influence of the network topology on the elastic behaviour is discussed.

Hydrogen bonded ferroelectric liquid crystal gels in freely suspended film geometry

We study freely suspended films of smectic C* liquid crystalline gels by means of polarizing microscopy. The gel point of the system is determined from the suppression of flow in the films. The network of hydrogen bonds is mechanically fragile but stabilizes orientation patterns of the sample, in particular it stores the texture present during gelation. Electro-optical experiments are performed to study the dynamics of the sample reorientation under the influence of in-plane electric fields. Mesogen orientation and optical properties can be switched in electric fields of a few kV m−1. After removal of electric fields, the network restores the ‘frozen-in’ texture. This texture can be erased by heating the films above the gelation temperature.

Inverse Piezoelectric and Electrostrictive Response in Freely Suspended FLC Elastomer Film as Detected by Interferometric Measurements

We report the electric field induced thickness variations of homeotropically oriented free standing films of a smectic (C* or A*) FLCE prepared from cross - linkable ferroelectric polysiloxanes. The changes in optical path length in free standing ferroelectric liquid crystal elastomer films have been detected by means of interferometric measurements at both the first and second harmonic of the exciting electric field (ω=33 Hz). The measured electrostrictive strain is above 2.7% (in the thickness direction) at a electric field around 1.5 MV /m. Our experiment reveal that the inverse piezoelectric and electrostrictive response increases sharply near the Sm-C* - Sm-A* phase transition temperature. Also X-ray reflection measurements on a spin cast FLCE film reveal the constriction of smectic layers.

Layer structure of free-standing smectic LC elastomer films

We probe the mesophase transitions and layer structures in thin ordered smectic liquid crystalline elastomer films by means of x-ray diffraction. Ordered elastomer films of submicrometer thickness are produced by crosslinking freely suspended smectic polymer films. After crosslinking - the mesomorphism is similar to that of the precursor polymer. The smectic layer spacing increases with temperature in the SmC* phase while it decays above the SmC*-SmA transition.

Nanomotoren aus Flüssigkristallen: Elektrostriktion

Herkommliche Hochleistungs-Piezomaterialien erreichen bei Anlegen elektrischer Spannung einen Hub von maximal 0, 1 % ihrer Langen. Arbeitsgruppen der Universtaten Leipzig und Mainz haben ein neues, ferroelektrisches Elastomer entwickelt, das auf Flussigkristallen basiert. Die Flussigkristallmolekule sind so in das Polymernetzwerk eingebunden, dass sie sich wie mikroskopische Hebel bewegen und Krafte ubertragen konnen. Bei einem elektrischen Feld von nur 1, 5 kV/mm andert ein frei tragender Film des neuen Materials seine Dicke um bis zu 4 %. Das ist Weltrekord und eroffnet vollig neue Felder fur technische Anwendungen.