Spin-coated side-chain liquid-crystalline polymer films, based on alternating copolymers of maleic anhydride and α-olefins carrying terminal mesogenic methoxybiphenylyloxy groups, on silicon wafers show lamellar ordering upon annealing above the glass transition temperature. In the surface topography (atomic force microscopy measurements), structures are visible with a height corresponding to a bilayer. Also within the film, the side chains are ordered perpendicularly to the surface as measured by X-ray reflectometry. There are indications that directly at the substrate surface the side chains are aligned parallel to the surface. By the two complementary techniques, a rather complete picture is obtained. Even though the films are very thin (nanometer-scale thickness), the structure has a high degree of perfection and the bilayer spacing is the same as measured for bulk polymer.

The stability against breaking-up of thin spin-coated films of liquid-crystalline polymers depends on the film thickness and annealing temperature. This study concerns side-chain liquid-crystalline polymers, based on alternating copolymers of maleic anhydride and mesogenic alkenes. The mesogenic group is a methoxybiphenyl. The as-prepared films are homogeneous and remain stable below the glass transition temperature. Upon annealing above this temperature, the films start to dewet. At the final stage of dewetting only droplets remain on top of a rather stable bilayer, which itself does not participate in the dewetting. This indicates autophobic behavior. The bilayer is even present above the isotropization temperature. In the mesophase we have a layered film, and dewetting may occur over several ordered layers. In all cases the dewetting is not linear in time and polymer slippage seems to take place on top of the stable bilayer. In the case of polymer slippage, a t 2/3 dependence is expected for the growth rate. That is indeed found above the isotropization temperature. In the mesophase the dewetting differs from the “normal” slippage behavior and a weaker time dependence is observed. Around the isotropization temperature there is a strong increase in the (initial) dewetting velocity of over more than 2 orders of magnitude, due to the sudden drop in viscosity.

The synthesis and characterization of liquid-crystalline polymers with possible good adhesive properties is reported. These polymers are prepared by alternating copolymerization of maleic anhydride and mesogenic alkenes. The spacer length m is varied (m = 2,3,4,6, 8 and 9) and methoxybiphenyl is used as the mesogenic group. The glass transition temperature decreases and the isotropization temperature increases with spacer length. Depending on the spacer length and temperature, Sg and SA,, mesophases can be observed. After annealing, spin-coated films of these polymers show very regular layered structures with a layer spacing similar to that in the bulk.

Liquid-crystalline polymers with maleic acid anhydride moieties in the backbone and methoxybiphenyl groups in the side chain have been investigated with respect to the ordering in and stability of thin films on chemically modified silicon substrates. For unmodified silicon wafers, it is known that the polymersubstrate interaction induces parallel layering in the film, resulting in rather stable films. When the surface groups are changed, i.e., by silylation, the interaction between the polymer and the surface can be tuned. This results in unstable films with a dewetting behavior that is strongly temperature and substrate dependent. At low temperatures in the mesophase holes nucleate, which are encircled by unstable rims. Upon annealing at higher temperature the rim instability decreases and the dewetting velocity increases. This feature also occurs for another completely different side-chain liquid-crystalline polymer with a methacrylate backbone and cyanobiphenyl groups in the side chains. We ascribe the peculiar dewetting behavior to the presence of polycrystalline domains in the thin films. Especially their size and orientation and their ability to deform under shear are held responsible for the rim instabilities and, consequently, for the droplets remaining behind in the dry patches.

The ordering process and kinetics in thin films (200-800-nm thick) of a thermotropic side-chain liquid-crystalline polymer have been investigated vertically and laterally, respectively, by x-ray reflectivity and atomic-force microscopy. The original smooth and amorphous spin-coated films initially become corrugated upon annealing in the smectic mesophase. The roughening of the surface results from the formation of randomly oriented microcrystalline domains in the film. At the same time, however, a laterally macroscopic crystal starts to grow from the substrate surface in the direction of the polymer-air interface at the expense of these domain structures. Finally, a nicely ordered single crystal with parallel-ordered bilayers is formed in the film as well as at the polymer-air interface. This one-dimensional crystallization, actually recrystallization, depends strongly on the temperature due to viscosity effects. At low temperatures, just above the glass-transition temperature, the ordering is very slow, but with increasing temperature the crystal growth is faster. An Arrhenius-type plot gives an activation energy of 122 kJ/mol, which we ascribe to the expected reorientations of the mesogenic groups during the recrystallization process.