Atomic force microscopy (AFM) has been used to modify a polyimide surface to give controlled liquid crystal (LC) alignment, and to examine the modification produced. Strong LC azimuthal anchoring was observed typically for normal forces >300 nN and line densities >5 μm−1, and optically diffracting LC elements were fabricated by repeatedly overpatterning the same area along different directions. Atomic force microscopy images showed little sign of topographic modification such as grooving, whereas lateral force images showed locally increased friction. Estimated contact pressures, 0.08–0.3 GPa, suggest shear-yielding occurs within a surface layer, causing polymer chain alignment. The AFM micromechanical interaction is compared with that occurring during the conventional cloth-rubbing LC alignment process.

The monolayer and LB film-forming properties of 20 structurally related amphiphilic octa-substituted phthalocyanine derivatives have been assessed. The molecular packing within examples of the films has been probed by visible-region spectroscopy and low-angle X-ray diffraction methods. Among derivatives where the aliphatic substituents are attached by ether linkages, there is a variation in the behaviour according to the length of the chains and whether or not the chains are branched. Films are not highly ordered but may contain domains of ordered structure, giving rise to r i redshifted absorption band in the visible spectrum. Analogues where the chains are attached by carbon-carbon bonds show superior monolayer behaviour and are excellent materials for deposition as LB films. Furthermore, there is good evidence from the spectra that change in the length of the alkyl chains provides a means of controlling the type of molecular packing within the films.

Liquid crystal ͑LC͒ surface alignment, which controls off-state contrast in LC displays, is commonly achieved by directional rubbing of polyimide-coated substrates. In order to better understand the alignment mechanism we have used tapping-mode atomic force microscopy to study the dependence of polymer surface morphology on rubbing conditions. Based on results from three polyimides rubbed at different strengths with two cloths, we have identified five surface feature types induced by the rubbing: ͑1͒ isolated point defects, ͑2͒ occasional deep scratches ͑у5 nm͒, ͑3͒ numerous very shallow scratches ͑mostly р1 nm deep͒, ͑4͒ nanoscale surface islands ͑3-10 nm high, number density Ͼ10 9 cm Ϫ2 ͒, and ͑5͒ modified background texture. The last feature confirms that the entire surface has been affected by the rubbing process. The finest resolution achieved, about 10 nm full width, was insufficient to resolve individual polymer chains. Of the features observed, only occasional very deep off-axis scratches clearly affected azimuthal LC alignment. Quasiperiodic features observed under weak rubbing conditions suggest that initial rubbing occurs by a stick-slip mechanism, and the widths of such features gives an estimate of fiber-surface contact size.

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