SANS STUDY OF A SEMIFLEXIBLE MAIN-CHAIN LIQUID-CRYSTALLINE POLYETHER

A main-chain semiflexible polyether (TPB-10) has been studied in the n ematic phase by small angle neutron scattering (SANS) and by neutron a nd X-ray diffraction. Principally, we have determined the polymer chai n conformation by SANS for mixtures of deuterated and hydrogenous poly mers, aligned using a strong magnetic field (4.2 T). In good agreement with previously reported results on nematic polyesters, our data are well fitted to a model of a cylinder in which the main chain forms one hairpin defect including two very confined and extended wires. Moreov er, the X-ray diffraction patterns show that smectic C fluctuations oc cur in the low-temperature nematic range. Referring to the layer norma l of the local S-C arrangement, the mesogens are tilted with respect t o the field. Strikingly, the whole chains are also tilted with the sam e angle as the mesogenic units.