Surface-Induced Phases in Melts

Variation of the preferential interaction of the block copolymer components with the substrate has proved to be an important tool for tuning the phase separation near the surfaces. The results of calculations in Fig. 10 quantify the effects of the surface fields in a solvent-free-cylinder-layer thick film. The variation of 6m at constant 

1 1 -5 0 Fig. 11 Effect of the strength of the film and at interfaces. Simulatk films (thickness = 54 nm = 9ao) wi face field C,v/. The isodensity profit Reprinted from [58], with permissh 5 he surface fielc n results for a th surfaces at z es (pji = 0.45) )n. Copyright 2 1 // 1 10 20 m on the phase sepai ylinder-forming A3B12. = 0 and at indicated vs ire shown for indicated )04 American Institute I I 25 30 ation in the interior of 43 (Cab = 6.5) in thick dues of symmetric sur-simulation parameters, jf Physics [58] 

The calculated phase behavior for asymmetric surface fields, where the interactions between the components and the top (cmi) and bottom (rM2) interface may vary freely, is even much richer (see Fig. 12 for two layers of structure) than for the symmetric case. A particular feature is the appearance of hybrid structures, which are either a coexistence of different surface reconstructions close to each of the interfaces or interconnected structures. Nevertheless, the general features of Fig. 12 can still be explained in terms of surface field and confinement effects, noting that each of the surface fields now supports its own surface reconstruction, which may interconnect for combinations of perpendicular and parallel structures. As in the symmetric case, this behavior is modulated by the film thickness via interference and confinement effects in a very complicated manner. 

Various experimental routes towards surface modification have been utilized in order to control the microphase separation in thin films, as well as to achieve large-area patterns with desirable orientation relative to the film plane [2, 19, 21, 51]. 

For a strong surface field and symmetric wetting conditions, a perforated lamella (PL) phase typically develops in up to four layers of structures, with an exception for the first layer of structures at the favored film thickness. For one layer and all transition regions between terraces a Cy phase was found. 

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