Smectic-C* elastomer

Figure 14. Idealized presentation of the orientation process, which leads to piezoelectricity in chiral smectic C elastomers (only the mesogens are shown) [28], P macroscopic polarization). The deformed states with a partially unwound helix (left and right) are prepared from the ground state with a helical superstructure (middle) by mechanical forces. 0 and direction of the spontaneous polarization in and out of the plane of drawing, respectively.

Hiraoka K, Sagano W, Nose T, Finkelmann H. 2005. Biaxial shape memory effect exhibited by monodomain chiral smectic C elastomers. Macromolecules 38 7352 7357. 

Schoenfeld, A., Kremer, F., Vallerien, S. U., Poths, H.. and Zentel, R., Collective and molecular relaxations in polymeric ferroelectric liquid crystals and experimental proof of piezoelectricity in chiral. smectic C-elastomers, Ferroelectrics, 121, 69-77 (1991). 

Semmler, K., and Finkelmann, H Orientation of a chiral smectic C elastomer by mechanic fields, Polym. Adv. Techno ., 5, 231-235 (1994). 

Fig. 9. Two-step deformation process of a chiral smectic C elastomer that displays macroscopic polarization at the end (31).

Smectic-C elastomers and especially chiral Sc elastomers have attracted a lot of interest as they can respond to electric stimuli or transfer mechanical stress into electrical signals. Owing to the C2-symmetry, chiral smectic-C phases show... 

Fig. 16 Smectic-C elastomer with uniform director orientation but conical layer distribution subjected to a second uniaxial mechanical deformation under an angle of 0 90° with respect to the first deformation axis (0 is the Sc tilt angle) [80, 116]...

Fig. 17 Smectic-C elastomer with uniformly aligned director but conical layer distribution subjected to shear strain perpendicular to the director [117] (a) and corresponding reorientation process that produces an Sc monodomain (b). Reprinted with permission from [87]. Copyright (2008) American Chemical Society...

Mauzac M, Nuyen HT, Toumilhac FG, Yablonsky SV (1995) Piezoelectric and pyroelectric properties of new polysiloxane smectic C elastomers. Chem Phys Lett 240(5-6) 461-466. doi 10.1016/0009-2614(95)00574-n... 

Hiraoka K, Kobayasi M, Kazama R, Finkelmann H (2009) Electromechanics of monodomain chiral smectic c elastomer mechanical response to electric stimulation. Macromolecules... 

The first chiral smectic C elastomer was synthesized by Zentel et al. in 1988 [13], [24]. The preparation of the network is similar to the synthesis of the cholesteric networks described above. The network was uniaxially stretched. An unwinding of the helicoidal superstructure is observed and an orientation of the director, as well as of the smectic layer normal roughly parallel to the stress axis occurs. A macroscopically uniform alignment of the sample was not observed as explained below. 

Figure 13.4. Electro-optical investigations at 2 Hz on a chiral smectic C elastomer. An unsymmetrical switching behavior is observed due to the network conformation (reproduced with permission from [25]).

Figure 13.5. Temperature-dependent pyroelectric investigations on a chiral smectic C elastomer. Two different cross-linking states were measured, (a) 0% cross-linking (polymeric state), (b) 5% cross-linking (transition temperatures (a) gi — 26°C c 18 °C Sc 85 °C i (b) gi — 28 °C c 23 °C S)) 77 °C i) (reproduced with permission from [28]).

Figure 13.6. Piezoelectric signal of a chiral smectic C elastomer as a function of the applied dynamic deformation at 35°C (A), 39°C (O), and 52°C ( ) (transition temperatures gi 1 °C S(( 81 °C i) (reproduced with permission from [15]).

Figure 13.9. Inverse piezoelectric signal of a chiral smectic C elastomer at 63 Hz as a function of the amplitude of the applied electric voltage, (A) without bias field, ( ) with bias field of 40 V (reproduced with permission from [38]).

Figure 13.10. Mechanical and electromechanical response of a chiral smectic C elastomer as a function of the temperature for four dilferent frequencies, (O) 0.158 Hz, ( ) 1.12DHz, (A) 11.2 Hz, (V) 100 Hz (transition temperatures g Sx 308 K Sc 333 K Sa 346 K i). (a) E mechanical storage modulus, E" mechanical loss modulus (b) g electromechanical storage coefficient, g" electromechanical loss coefficient (c) g electromechanical storage modulus, g" electromechanic storage modulus.

Ferroelectric chiral smectic C phases lack inversion symmetry, and are distinguished by spontaneous helicoidal electric polarization, The first experiment to measure SHG from ferroelectric liquid crystals was carried out [89] on unaligned samples under a dc electric field. Phase-matched SHG in ferroelectric liquid crystals has been carried out by using an electric field to unwind the helix [90]. Mechanical deformations in chiral smectic C elastomers have been shown to give rise to SHG [91]. A great deal of work has been carried out recently in studying SHG in ferroelectric liquid crys-... 

K. Semmler and R Finkclmaim, Orieniatiao of chiral smectic C elastomer by mechanical tkUa, Polymer Asha Teck 5 231 (1994)... 

Mukherjee PK. Isotropic to chiral smectic-C phase transition in chiral smectic-C elastomers. J Mol Liq 2013 187 266-71. 

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