Striped phase

Fig. 8.4 Crystal structures of a-Ca3(BN2)2 (a) and a-Sr3(BN2)2 (b) high-temperature phases. Striped atoms indicate partial occupations on special positions 8f (occupied by 7/8) and 2a (occupied by 1 /2).

Figure 4.1 Schematic cross-section of a centrifugal contact-separator (light gray = light phase, dark gray = heavy phase, striped = mixed phase).

Figure 3 High resolution electron micrograph for Cu-Au LXq ordered phase [29]. Black and white dots indicate different species and black stripes are Anti Phase Domain boundaries. The lattice mismatch across the domain boundary is clearly observed by referring to the guide lines in white.

Fig. 14. A snapshot of a configuration showing the stripe-like structure of the smectic phase formed hy the polar mesogen GB(3.0, 5.0, 1, 3) and the antiferroelectric compensation in adjacent layers. The different orientations of the dipoles are indicated hy the different shading of the ellipsoids...

Fig. 14.3 Polyhedral packing plots for the two-dimensional layers of [RE(P2S6),/2(PS4)P in the series of solids A2RE(P2S6)i/2(PS4), where A=K, Cs RE = Y, La. Rare-earth polyhedra are striped PS4 polyhedra are black phosphorous atoms in P2S6 are shown as black circles. Alkali atoms are not shown for clarity. Although these phases have distinctly different structures based on space group symmetry and atomic positions, the compounds are clearly related upon close inspection of the building blocks.

In the manufacture of aniline from nitrobenzene the reactor products are condensed and separated into an aqueous and organic phases in a decanter. The organic phase is fed to a striping column to recover the aniline. Aniline and water form an azeotrope, composition 0.96 mol fraction aniline. For the feed composition given below, make a mass balance round the column and determine the stream compositions and flow-rates. Take as the basis for the balance 100 kg/h feed and a 99.9 percentage recovery of the aniline in the overhead product. Assume that the nitrobenzene leaves with the water stream from the base of the column. 

As mentioned before, the stripe pattern deteriorates slowly with increasing number of Cu layers, but it remains visible for a long time. Eventually Cu clusters emerge with normal fee structure. In Fig. 24 an STM image of Au(100) is shown, the surface of which is covered by a nominally thick Cu overlayer. On top of the wavy Cu phase, clusters with regular bulk structure have been formed. A similar situation is depicted in Fig. 25 for Cu on Ag(100), where a large Cu crystallite with a flat... 

Fig. 21 Cyclic voltammogram and corresponding in situ STM images of 3 mM 4,4 -bipyridine (44-BP) on Au(lll) in 0.05 M KCIO4, scan rate 10 mV s-1. The sizes of the STM images are 10 x 10 nm2. The following 44-BP adlayer structures have been observed in the potential regions I, II, and III (a) high coverage densely packed phase, (b) striped structure, and (c) rhombohedral phase. The corresponding molecular orientations as derived from in situ IR studies on Au(l 11) are shown in panels (d-f) [303], The pairs of peaks Pl/Pl, P2/P2, and P3/P3 indicate first-order phase transitions between the respective adlayers [304]...

A very different model of tubules with tilt variations was developed by Selinger et al.132,186 Instead of thermal fluctuations, these authors consider the possibility of systematic modulations in the molecular tilt direction. The concept of systematic modulations in tubules is motivated by modulated structures in chiral liquid crystals. Bulk chiral liquid crystals form cholesteric phases, with a helical twist in the molecular director, and thin films of chiral smectic-C liquid crystals form striped phases, with periodic arrays of defect lines.176 To determine whether tubules can form analogous structures, these authors generalize the free-energy of Eq. (5) to consider the expression... 

Figure 5.51 Scenario for kinetic evolution of flat membranes into tubules.68,132 (a) When membrane is cooled into tilted phase, it develops stripes in tilt direction and then breaks up along domain walls to form ribbons, (b) Each ribbon twists in solution to form helix, (c) Helical ribbon may remain stable or may grow wider to form tubule. Reprinted with permission from Ref. 139. Copyright 2001 by the American Chemical Society.

However, further analysis of the behavior of the system in LC cells cast doubt on this interpretation. First, while intuitively attractive, the idea that relaxation of the polarization by formation of a helielectric structure of the type shown in Figure 8.20 would lower the free energy of the system is not correct. Also, in a thermodynamic helical LC phase the pitch is extremely uniform. The stripes in a cholesteric fingerprint texture are, for example, uniform in spacing, while the stripes in the B2 texture seem quite nonuniform in comparison. Finally, the helical SmAPF hypothesis predicts that the helical stripe texture should have a smaller birefringence than the uniform texture. Examination of the optics of the system show that in fact the stripe texture has the higher birefringence. 

While such behavior can be seen in achiral LC phases, driven by surface constraints as illustrated in Figure 8.11, further characterization of the phase responsible for the minority domains in the B2 banana phases shows this to be the first unequivocal example of a bulk fluid conglomerate. It is worth noting here that the EO behavior of the majority domains is achiral Stripes parallel to the layers switch to a SmA-like focal conic texture, which is identical for both signs of the field, as can be seen in Figure 8.22. This EO behavior very clearly appears achiral when observing the switching in motion. 

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