Ordered copolymers oriented crystallization

In liquid crystals or LC-glasses one looks for orientational order and an absence of three-dimensional, long-range, positional order. In liquid crystals, large scale molecular motion is possible. In LC-glasses the molecules are fixed in position. The orientational order can be molecular or supermolecular. If the order rests with a supermolecular structure, as in soap micelles and certain microphase separated block copolymers, the molecular motion and geometry have only an indirect influence on the overall structure of the material. 

We note that earlier research focused on the similarities of defect interaction and their motion in block copolymers and thermotropic nematics or smectics [181, 182], Thermotropic liquid crystals, however, are one-component homogeneous systems and are characterized by a non-conserved orientational order parameter. In contrast, in block copolymers the local concentration difference between two components is essentially conserved. In this respect, the microphase-separated structures in block copolymers are anticipated to have close similarities to lyotropic systems, which are composed of a polar medium (water) and a non-polar medium (surfactant structure). The phases of the lyotropic systems (such as lamella, cylinder, or micellar phases) are determined by the surfactant concentration. Similarly to lyotropic phases, the morphology in block copolymers is ascertained by the volume fraction of the components and their interaction. Therefore, in lyotropic systems and in block copolymers, the dynamics and annihilation of structural defects require a change in the local concentration difference between components as well as a change in the orientational order. Consequently, if single defect transformations could be monitored in real time and space, block copolymers could be considered as suitable model systems for studying transport mechanisms and phase transitions in 2D fluid materials such as membranes [183], lyotropic liquid crystals [184], and microemulsions [185],... 

Although most of the initial polymers and copolymers are no longer available, these systems should help us to investigate the details and structural consequences of a pre-ordering of the polymer melt, or the formation of a precursor crystal in polymer crystallization. From the present and as yet still sketchy results, it appears however that (a) if a crystal phase results from the transformation of a liquid crystal phase (usually of hexagonal symmetry), different orientations of the crystal unit cell are likely, which is not observed in conventional polymer crystallization (for example, in polyethy-... 

More recently, ordered ultradense arrays in block copolymer films have been obtained over macroscopic distances using faceted surfaces of commercially available single-crystal sapphire substrates [152]. The self-assembly overrides substrate defects and uses the topography only as a guide to the orientation of the arrays. 

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