The dynamics of a nematic side-group liquid-crystalline polymer (SG-LCP) melt are investigated using transient stress and birefringence measurements. This SG-LCP shows a pronounced drop in the dynamic moduli at sufficiently low frequency upon passing through the transition from the isotropic to the nematic state. In contrast to previous studies, this suggests that liquid-crystalline order does affect the relaxation dynamics of SG-LCP melts. In the isotropic phase we simultaneously measure dynamic birefringence and stress to determine the stress-optic ratio (SOR). Results in the isotropic state near Tn , show the anomalously large SOR characteristic of pretransitional effects in liquid-crystalline systems in general. In the nematic state, we find that prolonged, large-amplitude oscillatory shear dramatically reduces the turbidity and increases the birefringence of the sample, suggesting that shearing induces a preferred alignment in this SG-LCP melt. This is accompanied by a decrease in the effective dynamic moduli of the nematic.

Side group liquid‐crystalline polymers (SG‐LCP) will need to be macroscopically oriented if the applications foreseen for them are to be realized. The first observation of oscillatory‐sheer‐induced alignment of an SG‐LCP melt (the Figure shows a schematic of the rheo‐optical apparatus used) is reported. This discovery widens the potential applications of SG‐LCPs, but also raises fundamental questions regarding the mechanism of flow‐induced alignment.

Periodic director patterns in the magnetic-field induced splay Freedericks transition of a nematic side-group polysiloxane are reported. For this purpose liquid crystal cells (10 μm-500 μm) are studied by polarization microscopy as well as by deuteron NMR. Through this combinatin, the optically observed spatial dependence of the director can be quantitatively analyzed in terms of director distributions extracted from the NMR lineshape. In the equilibrium state of the Freedericks transition (static Freedericks effect), the director exhibits a one-dimensional periodicity perpendicular to the initial director orientation n0. The dynamics of the Freedericks transition involves a transient two-dimensional director pattern, representing convection rolls in which the nonlinear coupling between director rotation and viscous flow of the nematic (back-flow) leads to a reduction of the viscosity.

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