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The chemical composition and the preferential orientation of polymer segments at the surface of thin polyfluorene films have been investigated by carbon K-edge soft X-ray absorption spectroscopy, resolving the near-edge X-ray absorption fine structure (NEXAFS). The outermost surface layer of about 10 Å thickness exhibits a slight enrichment of alkyl side chains and a corresponding depletion of biphenyl groups. Moreover, at the film surface the plane of biphenyl rings comprising the polymer backbone is strongly oriented parallel to the film surface. This equilibrium surface characteristics of polyfluorene films are found to be caused mainly by the polymer/air interface rather than by the polymer/solid (silicon) interface. A significant reorientation of polymer segments occurs at the film surface upon rubbing with velour cloth, which results in a preferential orientation of polymer molecular axis (biphenyl ring axis) along the rubbing direction and a decrease in the in-plane orientation of biphenyl planes. Upon annealing a rubbed polyfluorene film in its nematic melt state, the rubbing-induced reorientation of polymer molecules disappears completely for a film of about 600 Å thickness, indicating that the rubbing-induced reorientation does not propagate much further beyond the surface region of polyfluorene films.

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Summary: A systematic investigation of the microstructure of ethylene copolymers has been carried out as a function of the comonomer type and content, employing small‐angle X‐ray scattering (SAXS) experiments to study the lamellar structure, and solid‐state NMR to study the local conformational freedom. The SAXS results clearly show that the major consequence of incorporating comonomers (butene and octene) is the absence of lamellar thickening during the crystallization. From solid‐state NMR study, applying the rotor‐encoded rotational echo double resonance technique (REREDOR), it is found that the extent of the orientational order in the noncrystalline region of semicrystalline polyethylene is substantial but this order is not significantly affected by the incorporation of comonomer units. Therefore, the major cause for the significant improvements of mechanical properties observed for ethylene copolymers is not a change in the thermodynamic state of the noncrystalline region, but most likely a significant change in the intermolecular topological structure due to the blocking of disentanglement processes required by the lamellar thickening step during crystallization.

We have synthesized and characterized the first cyclic co-oligomeric ferroelectric liquid crystals (FLCs) based on cyclic siloxanes and found that the co-oligomer containing two different mesogenic units exhibits SmC* mesophase over a wide temperature range from 65 o C to 135 o C, much wider than those of the monomer counterparts and the cyclic homo-oligomers. The cyclic co-oligomeric liquid crystal readily filled the display cell and exhibited fast switching times in the range of 4 ms to 6 ms over the entire SmC* phase. Moreover, the practical absence of layer shrinkage, attributed to de Vries-type transition, shows an additional significant advanage for cyclic co-oligomeric FLCs in LCD applications.