Ferroelectric liquid crystalline copolymers

Ferroelectric liquid crystals (FLC) are of great interest due to their fast electro-optical response which is about 1,000 times faster than conventional twisted nematic cells [131]. The geometry used is called a surface stabilized FLC cell which utilizes a very thin gap (=2 pm) to unwind the FLC supramolecular pitch (=1-2 pm) since the bulk FLC materials do not show macroscopic polarization. This very thin gap, however, leads to difficulties in manufacturing large panels and very poor shock resistance. Researchers have proposed the concept of microphase stabilized FLC [79,109, 130] using FLC-coil diblock copolymers for electro-optical applications as shown in Fig. 15. This concept takes advantage of ferroelectric liquid crystallinity and block copolymer microphase separation since the block... 

Time-resolved FTIR is used to study the structure and dynamics of ferroelectric liquid crystalline block copolymers. From analysis of the dynamic dichroism of the FTIR spectra, it was concluded that the components in the PS microphase are oriented randomly while the liquid aystalline groups form an ordered phase. The switching is of an electroclinic type, in which the tilt angle and the mesogenic motion increase with temperature, especially if the PS block is heated above Tg. The orientation of the liquid crystalline block after... 

Application of the concepts obtained in the study of PVDF and its copolymers has been made for other types of novel polymers with similar polar chemical structure. For example, poly(vinylidene cyanide) (PVDCN) and its copolymer with vinyl n-fatty acid ester have ciMmical structures close to that of PVDF F atoms arc displaced by CN groups. These polymers are also attracting attention because of their characteristic electric properties. Odd-numbered members of nylon (nylon 7, nylon 11, etc.) and ferroelectric liquid-crystalline polymers (FLCP) are also the candidates for ferroelectric polymers. These substances are still new. and their structural study has not yet been developed extensively compared with the study of PVDF and its copolymers. 

Figure 2. Structure of liquid crystalline block copolymers (LC-BCPs) (A) rod-coil diblock copolymer (B) rod-coil diblock copolymer with flexible spacer in the rod block (C) side group liquid crystal-coil (SGLC- coil) diblock copolymers (D) coil -rod-coil ABC triblock copolymers (predicted to be novel ferroelectric fluid by R. G. Petschek and K. M. Wiefling, Phys. Rev. Lett., 1987, 59(3), 343-346) (E) rod-rod diblock copolymer (one example of well-defined po-ly(n-hexyl isocyanate-fc-n-butyl isocyanate) rod-rod diblock copolymer was given by Novak et al. [68], however, no morphology studies were reported) (F) dendritic liquid crystal-coil (DLC-coil) diblock copolymer (not reported).

ChicUini. E., Galli, G.. Serhalti, E. I., Yagci, Yu., Laus, M., and Angeloni, A. S., Chiral liquid crystalline block copolymers based on polyether and mesogenic polyacrylate blocks, Ferroelectrics, 148, 311-322 (1993). 

Naciri, J., Pfeiffer, S., and Shashidhar, R., Fast switching ferroelectric side chain liquid-crystalline polymer and copolymer, Uq. Cry.%t., 10, 585-591 (1991). 

Naciri J, Pfeiffer S, Shashidhar R (1991) Fast switching of ferroelectric side-chain liquid-crystalline polymer and copolymer. Liq Cryst 10(4) 585-591. doi 10.1080/02678299108036446... 

In semicrystalline dipole electrets, polar crystallites are present in addition to the polar amorphous phase (Fig. 2b). In die technically most interesting semicrystalline dipole electrets such as polyvinyhdene fluoride (PVDF) and its copolymers with trifluoro ethylene (P(VDF-TrFE)) (Lovinger 1983) or hexafluoropropylene (P(VDF-HFP)), odd Nylons 7 and 11, polyureas, polyureflianes (PU), and some liquid crystalline polymers, the crystallites are ferroelectric (Vasudevan et al. 1979 Hattori et al. 1996). The terpolymer poly(vinyhdene-fluoride-trifluoroethylene— chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) has been shown to have relaxor ferroelectric properties as the CTFE group destabilizes die long-range order of the ferroelectric phase (Xu et al. 2001). 

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