Conformation SCLCP

Conformation of the better temporal stability of SCLCPs compared to that of isotropic SCPs that have similar chromo-phores has been made by Carr et al. [198]. These workers found that the polarization of the SCLCP 31PMA 6 is much more stable than that of the isotropic copolymer (31 PMA 3)o.9-(31 PMA 6)0.1 in spite of the fact that the Tg of the latter polymer is about 117 °C compared with 71 °C for the LC homopolymer. However, in this work, the better temporal stability of the LC polymer was related to the absence of fi relaxation, as shown by dielectric measurements. 

Using dynamic light-scattering measurements [Jamieson et al, 1996], Syi was determined for nematic solutions of a SCLCP, which had a weakly prolate or oblate conformation (i.e., R /R l), based on ER measurements of Sr]b and Srjc, and indicated [Liu et al, 1999] that Syi ckTtR/N, whereas the Brochard model predicts [via Eq. (1.95)] that Syi 0. 

As a test of the revised theory, further experiments were conducted [Zhao et al., 2005] on nematic solutions of a SCLCP. ER measurements indicated, via application of the Brochard hydrodynamic model, a slightly prolate conformation, R /R = 1.17 0.02, consistent with small-angle neutron scattering measurements, which indicated, that= 1.12 0.06. Observations of the shear stress transient response of a homeotropic monodomain indicated that at a concentration between 0.01 and 0.02 g/mL, the solution exhibited a transition from director-aligning to director-tumbling behavior. The latter result is inconsistent with the original Brochard model [see Eq. (1.94)], which predicts such a transition (i.e., Sas > 0) only for a polymer with an oblate shape but agrees with the modified theory [Eq. (1.96)]. 

The mesogenic units can also be attached as pendants to a flexible backbone through flexible spacers (see Fig. 4.13), resulting in a completely new class of polymers with unique properties, so-called the side chain liquid crystal polymers (scLPC). scLCP manifest a unique competition between the tendency of the mesogenic units towards anisotropic liquid-crystalline order and the tendency of the backbone chain towards isotropic chain conformation. The liquid-crystalline order influences the polymer chain conformations and vice versa. The flexible... 

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