Flexoelectric polymers

The remainder of this book is organized into sections covering each of the main classes of EAPs. The first chapter of each section focuses on the fundamentals of each technology, describing the actuation mechanism and performance. Two of the classes listed in Table I.l, carbon nanotubes and flexoelectric polymer actuators, have not been included... 

Finally, it is worth mentioning that a phenomenon analogous to the difference between the normal and giant flexoelectricity of calamitic and bent-core nematics, respectively, exists in crystals, ceramics and polymers too. The flexoelectric response (defined in Eq. (3.1)) of perovskite-type ferroelectrics, " of relaxor ferroelectric ceramics and polyvinylidene fluoride (PVDF) films are four orders of magnitude larger than the flexoelectricity of dielectric crystals. In those sohd ferroelectric materials the polarization induced by flexing is evidently of piezoelectric origin. 

M. Marvan and A. Havranek, Flexoelectric effect in elastomers, In ed. I. Chudacek, Relationships of Polymeric Structure and Properties, Progress in Colloid and Polymer Science. Vol. 78, Springer-Verlag, New York, 1988. pp. 33-36. doi 10.1007/BFb0114342... 

Let us now briefly describe electrohydrodynamic instabilities in polymer nematics. The first observation of the Kapustin-Williams domains in nematic polymers were reported in [117, 118]. The qualitative picture of the phenomenon is, in fact, the same as that for the conventional nematics (domains perpendicular to the initial director orientation in a planar cell, typical divergence of the threshold voltage at a certain, critical frequency, etc.). The only principal difference is a very slow dynamics of the process of the domain formation (hours for high-molecular mass compounds [117]). The same authors have observed longitudinal domains in very thin samples which may be referred to as the flexoelectric domains [5-14] discussed in Section 5.1.1. 

This book was conceived as a renewed version of the earlier published original book, Electro-Optical and Magneto-Optical Properties of Liquid Crystals (Wiley, Chichester, 1983) written by one of us (L.M. Blinov). That book was first published in Russian (Nauka, Moscow, 1978) and then was modified slightly for the English translation. Since then new information on electrooptical effects in liquid crystals has been published. Novel effects have been discovered in nematics and cholesterics (such as the supertwist effect), and new classes of liquid crystalline materials, such as ferroelectric liquid crystals, appear. Recently, polymer liquid crystals attracted much attention and new electrooptical effects, both in pure polymer mesophases and polymer dispersed liquid crystals, were studied. An important contribution was also made in the understanding of surface properties and related phenomena (surface anchoring and bistability, flexoelectricity, etc.). 

Chu B, Salem DR (2012) Flexoelectricity in several thermoplastic and thermosetting polymers. Appl Phys Lett 101 103905... 

Newnham RE, Sundar V, Yimnirun R, Su J, Zhang QM (1997) Electrostriction nonlinear electromechanical coupling in solid dielectrics. J Phys Chem 101 10141-10150 Ploss B, Ploss B, Shin FG, Chan HLW, Choy CL (2000) Pyroelectric or piezoelectric compensated ferroelectric composites. Appl Phys Lett 76 2776-2778 Poddar S, Ducharme S (2013) Measurement of the flexoelectric response in ferroelectric and relaxor polymer thin films. Appl Phys Lett 103 202901... 

In addition to the TN and IPS modes in nematic displays, himdreds of other displays methods were invented and tested over the last 30 years. Out of them the bistable nematic development based on surface flexoelectric interactions, the bistable cholesterics displays based on switching between planar and focal conic textures and the polymer dispersed liquid crystal displays found some applications. None of them, however, offer better than a few milliseconds switching time. 

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