Ferroelectric liquid crystalline elastomers, 2. Variation of mesogens and network density

Oriented smectic-C* elastomers have been made by performing radical photo-crosslinking reactions in a polar state of the ferroelectric phase. This paper aims at the evaluation of structure-property-relationships. Two polymer systems – varying in the length of the mesogens, the ferroelectric polarization and the amount of crosslinkable groups – were synthesized. The ferroelectric properties of the resulting elastomers were studied using electro-optical investigations. The crosslinking of ferroelectric polysiloxanes with a modest polarization (50–105 nC/cm2) and 15 or 25 mol-% of crosslinkable groups leads to polar elastomers, which can no longer be switched completely (voltages up to 400 V are not enough to reach the second, destabilized switching state). Ferroelectric polysiloxanes with a higher polarization (90–150 nC/cm2) lead to elastomers, which can be switched again completely. This happens because the torque (Ps·E) acting on the liquid crystalline director is – this time – large enough to overcome the elastic field of the polymer network.