Ordering anticlinic

All the modifications of the a form would present, perpendicular to the b axis, macromolecular bilayers including all isoclined chains. A regular succession of bilayers with anticlined helices would correspond to the limiting ordered modification (a2), while a statistical succession of bilayers would correspond to the limiting disordered modification (a ) [40]. 

In the a modifications of i-PP, bilayers of macromolecules are stacked one on the top of the other in such a way that the top layer on one bilayer and the bottom layer of the bilayer in contact are made up of helices which are enantiomorphous. such helices are regularly anticlined for the ordered a2 modification, more or less at chance isoclined or anticlined for the disordered modifications. 

Figure 1. Transverse section of barley leaf epidermal cells taken perpendicular to the long axis of the cells and anticlinal to the leaf surface. The section has been labeled by the EMSIL technique (see Methods) utilizing purified C. sativus endopolygalacturonase and monoclonal antibody EPG-4, which is specific for this enzyme, in order to localize the substrate of the enzyme at the typical site penetrated by the fungal pathogen. Bar = 1 pm. Inset Comparable cell wall region as in Fig. 1 but labeled with monoclonal antibody JIM 5 to localize non-esterified pectin. Bar = 1 pm. Note the identical labeling patterns obtained with either method.

It is interesting to point out here that with all of the theoretical speculation in the literature about polar order (both ferroelectric and antiferroelectric) in bilayer chevron smectics, and about reflection symmetry breaking by formation of a helical structure in a smectic with anticlinic layer interfaces, the first actual LC structure proven to exhibit spontaneous reflection symmetry breaking, the SmCP structure, was never, to our knowledge, suggested prior to its discovery. 

Chirality (or a lack of mirror symmetry) plays an important role in the LC field. Molecular chirality, due to one or more chiral carbon site(s), can lead to a reduction in the phase symmetry, and yield a large variety of novel mesophases that possess unique structures and optical properties. One important consequence of chirality is polar order when molecules contain lateral electric dipoles. Electric polarization is obtained in tilted smectic phases. The reduced symmetry in the phase yields an in-layer polarization and the tilt sense of each layer can change synclinically (chiral SmC ) or anticlinically (SmC)) to form a helical superstructure perpendicular to the layer planes. Hence helical distributions of the molecules in the superstructure can result in a ferro- (SmC ), antiferro- (SmC)), and ferri-electric phases. Other chiral subphases (e.g., Q) can also exist. In the SmC) phase, the directions of the tilt alternate from one layer to the next, and the in-plane spontaneous polarization reverses by 180° between two neighbouring layers. The structures of the C a and C phases are less certain. The ferrielectric C shows two interdigitated helices as in the SmC) phase, but here the molecules are rotated by an angle different from 180° w.r.t. the helix axis between two neighbouring layers. 

The analysis of these 25 compounds confirms the flexibility of dpg/dpg+. It can adopt a propeller like conformation and induce the formation of chiral crystals. It establishes predominantly two-dimensional H-bonding networks with the counter ion. From the perspective of the crystal engineer, an anticlinal conformation would maximize the non-linear properties of the molecule. However the non-linear optical response depends greatly on the molecular alignment. Non-centrosymmetric dispositions have not yet been achieved for dpg with an anti-anti conformation. The best strategy to attain NLO samples is by inducing a syn-anti conformation where a propeller structure might induce a chiral disposition of molecules and thus a non-centrosymmetric order. Another successful approach is to force crystallization with a chiral counterion. 

In the 1990-ies Georgian geological institutions were carrying out survey studies in order to determine and investigate some favourable structures for UGS facilities. These appropriate structures of brachyanticlines and anticlinal domes within folds consisting also of such rocks can be used as gas reservoirs (mainly cracked sandstones, tuff sandstones and tuff breccias). They are displayed at depths around 1000-1500 meters - sometimes even more than 2000 meters - and are covered with waterproof and gas-proof limestone rocks, with capacities estimated at 1-1.5 bcm [8],... 

Further studies by Nishiyama et al. [34-45] showed that when taken in isolation, only one of the aromatic units within a supermolecular system has a propensity to exhibit liquid crystal phases, then the supermolecular material itself could be mesomorphic, see Fig. 5. For example, for the top molecular structure, 5 [45], in Fig. 5, only the biphenyl unit at the center of the structure supports mesophase formation, whereas the benzoate units are too isolated from the biphenyl moiety in order to affect mesomorphic behavior. The second material, 6 [45] has terminal phenyl units, which are only connected by aliphatic chains to the benzoate units. Thus in this case, the material has four aromatic units out of six which are not in positions that can enhance mesophase formation. However, the second material has similar transition temperatures and phase sequences to the first, i.e., both materials exhibit an unidentified smectic phase and a synclinic ferroelectric smectic C phase. If the third material, 7 [38], is examined, it can be seen that the mesogenic unit at the center of the supermolecule is an azobenzene unit which is more strongly supportive of mesophase behavior than the simple biphenyl moiety. Thus the clearing point is higher for this material in comparison to the other two. The attachment of the terminal phenyl unit is by a methylene spacer of odd parity, and as a consequence the smectic C phase has an anticlinic structure rather than synclinic. 

The two polarizations Pp and Pap may be taken as secondary order parameters coupled with the genuine order parameters. As a result, depending of the model, the theory predicts transitions from the smectic A phase into either the synclinic ferroelectric phase at temperature Tp or into an anticlinic antiferroelectric phase at Tap- One intermediate ferrielectric phase is also predicted that has a tilt plane in the i + 1 layer turned through some angle

tilt plane in the i layer. The models based on the two order parameters are of continuous nature (9 may take any values) and, although conceptually are very important, caimot explain a variety of intermediate phases and their basic properties. 

Zalar B, Gregorovic A, Blinc R (2000) Interlayer molecular exchange in an anticlinically ordered chiral liquid crystal. Phys Rev E 62 R37-R40... 

Liquid crystal molecules usually tilt in the same direction over the smectic layers (synclinic [212]) in the smectic C (SmC) phase. However, in one of the smectic A (SmA) phases, called de-Vries phase [213,214], molecules tilt but the tile direction is random so that the overall molecular tilt cannot be recognized optically. Frustration can be produced between aligning and random orders [215]. There is another style of tilt, in which the tilting direction is aligning in one direction in each smectic layer however, tilting direction alternates between the adjacent layers (anticlinic [212]). It has been well known that the introduction of chirality into the synclinic and anticlinic stmctures produces the ferroelectric and antiferroelectric properties, respectively. Frustration between the ferroelectric and antiferroelectric properties produces the ferroelectric structure in which the spontaneous polarization is partially canceled by the different magnitude between plus and minus polarization directions [216, 217]. The anticlinic order, NOT the antiferroelectric order, has been reported to be created by achiral systems [218, 219], indicating that the frustration between synclinic and anticlinic structures occurs, without any polar effects. The clinicity is determined by the style of the molecular order between the adjacent smectic layers, and therefore, the molecular structures at the peripheral... 

In principle, we can also envision that only the director h is tilted with respect to the layer normal k. Successive smectic layers can be either ferroelectric (with the same direction of polar order) or antiferroelectric (with opposite directions). Likewise, successive layers can be either synclinic (with the same direction of molecular tilt) or anticlinic (with opposite tilt directions).Those situations are illustrated in the bottom row of Figure 2-3. To distinguish from the tilt of the molecular plane (which is denoted by the symbol C to express clinic ), the tilt of the long axis will be called leaning and will be labeled with L. Just as in the SmCP cases we can have four distinct sub-phases SmL P, SmL P, SmL P and SmLgP depending on the subsequent tilt and polarization direction combinations. In such phases the polar axis is not parallel to the smectic layers and they have Cg symmetry. 

Chirality can also be introduced when one or more chiral carbons are incorporated in the molecules, for example in the hydrocarbon terminal chains [67, 68], within the bent-core [69], or by addition of chiral dopants [6, 70], It was noted during the early research that the handedness of the homochiral structures is very sensitive to chiral dopants [6], or even on chiral surfaces [71]. On the other hand, it was observed that banana-smectics made of enantiomeric chiral molecules form synclinic - antiferroelectric [44] and anticlinic ferroelectric [67] domains. This combination of tilt and polar order implies that the phase is racemic, with a rigid alternation of right- and left-handed chiral layers. This shows that the molecular chirality has no or minor effect on deciding about anticlinic or synclinic packing (which is mainly determined by entropic reasons), but it can bias the otherwise degenerate tilt directions. 

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