Polyacrylic liquid crystals

Fig. 4.23. Summary representation of the temperature dependence of the relaxation rate for five different dielectric relaxation processes observed in side chain polyacrylate liquid crystals. Tg denotes the glassy transition, and I, N, and S stand for the isotropic, nematic and smectic phases, respectively. The broken line represents results of NMR investigations (see text).

Fig. 4.24. Schematic representation of different molecular motions involved in the dielectric relaxation of polyacrylic liquid crystals.

Photochromic materials with liquid-crystal polymer40 2 are interesting advanced materials, due to their sensitivity to light, electric, and magnetic fields. Copolymers of polyacrylic or polysiloxane backbone, con-... 

The use of an electric field is not the only effective way to influence the LC polymer structure, magnetic fields displays a closely similar effect167 168). It is interesting as a method allowing to orient LC polymers, as well as from the viewpoint of determining some parameters, such as the order parameter, values of magnetic susceptibility, rotational viscosity and others. Some relationships established for LC polymer 1 (Table 15), its blends with low-molecular liquid crystals and partially deuterated polyacrylate (polymer 4, Table 15) specially synthesized for NMR studies can be summarized as follows ... 

The concept of a side chain liquid crystal polymer has been demonstrated in a number of laboratories and is well documented in the literature (J ). Most of the side chain liquid crystalline polymers reported to date contain polysiloxane, polyacrylate or polymethacrylate main chains. More recent studies on the effect of backbone flexibility now include the use of flexible poly(ethylene oxide) or more rigid poly( a-chloroacrylate) chains. 

The same was observed for the following two polymers (3.44) and (3.45) with the mesogenic units of a schiff base structure (Frosini et al, 1981). The polyacrylate is a smectic liquid crystal from 93 °C to 258 °C. The polymethacrylate does not form any liquid crystalline phase. 

Nevertheless, several authors, in studying SmC polyacrylates [22] or SmC poly-siloxanes [ 14,41,67], have observed the two expected collective relaxations in ferroelectric liquid crystals, namely the Goldstone mode and the soft mode. These two relaxations occur at frequencies lower than 10 Hz. 

Leclair S, Mathew L, Giguere M, Motallebi S, Zhao Y. 2003. Photoinduced alignment of ferroelectric liquid crystals using azobenzene pol5mier networks of chiral polyacrylates and polymethacrylates. Macromolecules 36 9024 9032. 

Using functional molecules as structural directors in the chemical polymerization bath can also produce polyaniline nanostructures. Such structural directors include surfactants [16-18], liquid crystals [19], polyelectrolytes (including DNA) [20,21], or complex bulky dopants [22-24]. It is believed that functional molecules can promote the formation of nanostructured soft condensed phase materials (e.g., micelles and emulsions) that can serve as soft templates for aniline polymerization (Figure 7.3). Polyelectrolytes such as polyacrylic acid, polystyrenesulfonic acid, and DNA can bind aniline monomer molecules, which can be polymerized in situ forming polyaniline nanowires along the polyelectrolyte molecules. Compared to templated syntheses, self-assembly routes are more scalable but they rely on the structural director molecules. It is also difficult to make nanostructures with small diameters (e.g., <50 nm). For example, in the dopant induced self-assembly route, very complex dopants with bulky side groups are needed to obtain nanotubes with diameters smaller than 100 nm, such as sulfonated naphthalene derivatives [23-25], fidlerenes [26], or dendrimers [27,28]. 

Figure 2.11. Polarized light microscopy of polyacrylate-silica aerogel composites obtained by phoVipolymeriza-tion of octylcyanobiphenyl liquid crystal infiltrated in the porosity of the aerogel (in the cliche, liquid crystal and silica aerogel are, respectively, the brilliant and opaque phases). Courtesy ofPesce da Silveira N (UFRGS, Porto Alegre, Brazil) and Rigacci A. [99].

There are two main approaches to the synthesis of side-chain FLCPs. The first one consists of the synthesis of low-molar-mass mesogenic molecules having a polymerizable group at the molecular end, with further polymerization (Fig. 6a). (It should be noted that the monomers themselves are often, although not necessarily, ferroelectric liquid crystals.) In that way, many dozens of ferroelectric LC polyacrylates and polymethacrylates have been synthesized. 

Tabrizian, M., Bunel, C., Vairon, J. P, Friedrich, C., and Noel, C., Liquid-crystalline polyacrylates containing biphenyl and chiral terminal groups in the side chain. 1. Influence of the spacer length on the liquid-crystal behaviour, Makromol. Chem., 194, 689-704 (1993). 

Verrall, LM., Beattie, D., Coates, D., Sage, I., and Lymer, K., 1996. Ferroelectric switching liquid crystal polyacrylates—the control and effect of molecular weight, Ferroelectrics, 181, 327-335 (1996). 

Leroux N, Keller P, Achard MF, Noirez L, Hardouin F (1993) Small-angle neutron-scattering experiments on side-on fixed liquid-crystal polyacrylates. J Phys 11 3(8) 1289-1296. doi 10.105 l/jp2 1993199... 

Fujiwara et al. [147] used DSC to follow the interactions between multilamel-lar vesicles of dipalmitoylphosphatidylcholine (1.4 mM) and polyacrylic acid as a function of pH. The thermograms showed the gradual disappearance of a small pretransition peak at 35 C and of the main transition peak (sharp) at 41°C, with the simultaneous appearance of a broad peak at 44°C as the pH was lowered from 7.6 to 3.8. At the latter pH value, only the 44°C peak was seen (Fig. 16). The peak at 41°C corresponds to pure vesicles, whereas the one at 44°C is due to the vesicles interacting with polyacrylic acid. The sum of the enthalpies of these peaks remained constant. Hence, the gel to liquid crystal transition tempera-... 

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