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RESEARCH PRODUCT

Polymers, Ferroelectric Liquid Crystalline Elastomers

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Ferroelectric materials are a subclass of pyro- and piezoelectric materials. They are very rarely found in crystalline organic or polymeric materials because ferroelectric hysteresis requires enough molecular mobility to reorient molecular dipoles in space. So semicrystalline polyvinylidene fluoride (PVDF) is nearly the only known compound. On the contrary, ferroelectric behavior is very often observed in chiral liquid crystalline materials, both low molar mass and polymeric. Ferroelectric LC-elastomers represent an interesting class of material because they combine the ordering of liquid crystalline ferroelectric phases and the rubber elasticity of polymer networks. Switching of the electric polarization leads to deformation of the polymer network, equivalent to stretching a spring, and creates a stress in the network of polymer chains. The interaction of mesogens and the network can be varied by using different topologies of net points: Crosslinking is carried out either within the siloxane sublayers (leading to fast switching elastomers) or between the siloxane sublayers (resulting in an elastomer that favors the ferroelectric switching state in which the cross-linking reaction took place). Because the orientation of the smectic phase couples to the polymer network, electromechanical measurements show a piezoelectric effect. Mechanical deformation leads to polarization or an external electric field to deformation of the sample. Applying the electric field parallel to the smectic layer structure leads to an extremly high electrostrictive strain of 4% in an electric field of only 1.5 MV/m. Keywords: Ferroelectric liquid crysatlline elastomers; Synthesis; Properties; Characterization