Ferroelectric block 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).

It is our belief that block copolymers containing LC segments are materials with novel and unencountered properties which will offer great opportunities for developing high performance materials. Here we would like to give two examples. One example is a microphase stabilized ferroelectric liquid crystal (MSFLC) [109] for potential flat panel display applications, while the other is a material for stable, low surface energy [110] application. 

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... 

FIGURE 7 Structural derivatives of side-chain ferroelectric LC homopolymers (a) diluted copolymers (b) block copolymers. 

Another novel approach to the structural modiflcation of side-chain ferroelectric homopolymers has been proposed by Chiellini et al. [37,38]. Chiral block copolymers (Fig. 7b) are prepared by decomposition of the azo macroinitiator 1, which starts the chain polymerization giving macroradical 2. The polymerization terminates by combination of two macroradicals resulting in ABA triblock copolymer 3. 

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). 

Chandran A, Prakash J, Naik KK, Srivastava AK, D browski R, Czerwinski M, Biradar AM (2014) Preparation and characterization of MgO nanoparticles/ferroelectric liquid crystal composites for faster display devices with improved contrast. J Mater Chem C 2 1844-1853 Chatterjee T, Mitchell CA, Hadjiev VG, Krishnamoorti R (2012) Oriented single-walled carbon nanotubes-poly(ethylene oxide) nanocomposites. Macromolecules 45 9357-9363 Chiu JJ, Kim BJ, Kramer EJ, Pine DJ (2005) Control of nanoparticle location in block copolymers. J Am Chem Soc 127 5036-5037... 

The supramolecular structure of block co-polymers allows the design of useful materials properties such as polarity leading to potential applications as second-order nonlinear optical materials, as well as piezo-, pyro-, and ferroelectricity. It is possible to prepare polar superlattices by mixing (blending) a 1 1 ratio of a polystyrene)-6-poly(butadiene)-6-poly-(tert-butyl methacrylate) triblock copolymer (SBT) and a poly (styrene)-Apoly (tert-butyl methacrylate) diblock copolymer (st). The result is a polar, lamellar material with a domain spacing of about 60 nm, Figure 14.10. 

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