Small Angle Neutron Scattering Study of Comb-Like Liquid Crystal Polysiloxane Macromolecule Conformation in Smectic Phase

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Abstract
The conformation of the main chain of the comb-like liquid crystalline polysiloxane with CN-containing biphenyl side groups (average polymerization degree 63) oriented in magnetic field was investigated in the smectic phase by small angle neutron scattering (SANS). The conformation is characterized by two projections of the radius of gyration R|| =10.9Å and R|| = = 17.2Å measured with the scattering vector along and perpendicular the smectic layers normal, respectively. The data are interpreted in the frame of the model assuming that the macromolecule backbone divides itself into quasi-two-dimensional subcoils, randomly placed in the neighboured, mainly alkyl, sublayers separated by the aromatic ones. The subcoils are connected with each other by the tie segments of the main chain accomplishing random walks through the mesogenic layers. The tie segments can be considered as defects in the smectic phase.