Smectic C structure and backbone confinement in side-on fixed liquid crystalline polymers

The influence of the rate of dilution of the mesogens along the polymer bac kbone on the conformation and the structure of two different side-on mesoge ns polysiloxanes are studied using neutron-scattering techniques. The avera ge backbone conformation in the nematic and smectic C phases is deduced fro m small-angle neutron-scattering measurements. An inversion in the backbone conformation from prolate in the nematic phase to highly oblate in the sme ctic phase is evidenced. Distribution profiles of polysiloxane main chains are calculated from neutron diffraction experiments in the smectic phase. A transition in the confinement of the main chain within the layers has been demonstrated: the polymer backbone can be segregated between the layers, b ut also present in the middle part of the mesogenic layers.