Contrast structures phase transition models

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],... 

As to the transition aluminas, the literature up to 1977 has been reviewed by Knozinger and Ratnasamy. In this contribution, the authors also discuss the possible structures of the surface starting from the bulk structure of defective spinels typical of transition aluminas. It is assumed that the T7-phase preferentially exposes the (HI) face and the 7-phase the (110) face. By this, both octahedral and tetrahedral ions are at the surface, in contrast with earlier models, which only envisaged octahedral cationic sites. The situation is further complicated by the fact that both in the case... 

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