Orientation SCLCP

SCLCPs combine liquid crystalline properties and polymeric behavior in one material. If the mesogenic unit is fixed directly to the polymer main chain, the motion of the liquid crystalline side chain is coupled with the motion of the polymer backbone, preventing the formation of a LC mesophase. Therefore, Finkelmann and Ringsdorf proposed that the introduction of a flexible spacer between the main chain and the mesogenic unit would decouple their motions, allowing the mesogenic moiety to build up an orientational order [29,30]. 

One of the most interesting features of SCLCPs is related to the fact that a liquid crystalline phase can be orientated and frozen by cooling it to below the glass transition temperature. It is therefore necessary to drive SCLCP systems from microscopic self-organized mesophases to macroscopic order. 

The techniques used to obtain the untwisted SmC phase structure in low molar mass LCs and SCLCPs are limited to thin layers. In contrast to this, LC elastomers can be macroscopically uniformly oriented by mechanical deformations [230], and this orientation process is not limited to thin samples or suitable dielectric anisotropy of the material. Furthermore, for LC elastomers the oriented structure can be chemically locked in by crosslinking, resulting in the so-called liquid single crystal elastomers [231],... 

Figure 11.5. Changes in orientation of azobenzene mesogens for two films of azo-SCLCP-grafted SBS, under 500% strain, subjected to repeated cycles of unpolarized UV irradiation for orientation loss and unpolarized visible irradiation for orientation recovery. Source Bai and Zhao, 2001. Reprinted with permission.

Figure 11.7. Schematic iiiustration of (a) the anisotropic morphology of stretched SBS and (b) the periodic presence of disordered c/s-azobenzene and oriented trans-azobenzene in irradiated and nonirradiated fringes, respectively, for both perpendicular and parallel gratings recorded on azo-SCLCP-grafted SBS. Source Bai and Zhao, 2002. Reprinted with permission.

It has been demonstrated that the photo-induced orientation of dye-containing SCLCPs can be used for reversible optical data storage [85 90]. FTIR polarization spectroscopy has been applied to monitor the orientation of the main chain and the mesogenic side-chains which are of critical importance in these storage processes [15, 91-94]. Here, some results obtained by laser irradiation of a homologous series... 

In addition to the diffuse crescents and the Bragg spots, the X-ray patterns for oriented Sa and Sc SCLCPs can show parallel diffuse lines equally spaced versus This is characteristic of disorder... 

Very sparse dielectric studies of polysiloxane scLCPs below the glassy transition show evidence of only one relaxation process, similar to the -process in polyacrylates, with a very broad distribution of relaxation times.The temperature dependence is Arrhenius and the activation energy of 51 kJ mol matches that of the jSi-process in poly acrylates (see above). Measurements performed on the oriented smectic glass show that... 

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