Mesophases molecular geometry

The subsequently so-called mesophase combines its fluidity with some typical anisotropic properties of the solid, crystalline state, for example birefringence. In the years which followed this phenomenon became the subject of intensive study [3] and it was found that many compounds with rod-like molecular geometry formed liquid crystalline phases [4]. 

Figure 3. Sketch of the principal phase behavior of amphiphilic compounds. Usual amphiphiles are represented by a vertical line in this scheme they exhibit only one type of mesophase. Extreme geometries of one of their molecular parts or the addition of solvents (linear alkanes or water) may lead to a deviation from the vertical orientation of that line, thus, amphiphilic compounds in such situations may form various types of liquid crystal phases T = temperature, SmB phase (rotator phase), Cubjn and Cub(,i = cubic discontinuous or cubic bicontinu-ous phases, respectively, Col, i = columnar hexagonal phase, Iso = isotropic phase.

In the same paper, the effect of chlorination of some derivatives was also described (143). The introduction of the chlorine in either the 3- or 5-position suppressed the mesomorphic properties of the ligands, probably due to the slight deviation from the planarity (3-position) and to the steric hindrance (5-position). The effect on the copper complexes was more interesting (Table 60). The chlorine atom in the 3-position did not perturb the molecular geometry of the complex significantly, but there was stiU a slight reduction in the mesophase stability as well as the... 

The origin of LC phases is rooted in molecular geometry. The most common shapes of LC molecules are rod-like, disc-like, and, in some cases, lath-like [1]. For LC molecules with different shapes, different mesophases may be formed. Rod-like molecules form nematic, smectic, and cholesteric phases. In addition, several rod-like compounds exhibit cubic mesophases. The reason for... 

The term mesophase is used in reference to the liquid crystalline phase, and the molecular (sub)structures that give rise to this phase are termed mesogens. Macromolecules with rod-like or a flat, disc-like geometries tend to form such... 

Thermotropic liquid crystals can then be furflier subdivided into high molecular mass, main and side-chain polymers [10] and low molecular mass, the latter class of compounds being one of the areas of this review. The phases exhibited by the low molecular mass molecules are then properly described with reference to the symmetry and/or supramolecular geometry of the phases, which are briefly introduced here and are discussed in more detail further below. Thus, the most disordered mesophase is the nematic (N), which is found for calamitic molecules (N), discoidal molecules (Nq) and columnar aggregates (Nc), among others. The more ordered lamellar or smectic phases (S) [11, 12] are commonly shown by calamitic molecules, and there exists a variety of such phases distinguished by a subscripted letter (e. g. Sa, Sb)- Columnar phases (often, if incorrectly, referred to as discotic phases) may be formed from stacks of disc-like molecules, or from... 

In the palladium(II) macrocyclic complexes, the metal ions were proposed to be coordinated in a square planar geometry, with a disordered smectic mesophase being observed, even for the polycatenar complexes (i. e. those with more than one chain on each terminal ring). Preliminary X-ray diffraction measurements determined the smectic if-spacing to be 53 A which is comparable to the calculated molecular length of the ligand (50-52 A) in the fully extended conformation [83b]. 

Due to the disc-like geometry of the porphyrin macrocycle, discotic mesophases have generally been the most common for porphyrin liquid-crystalline materials. The first porphyrin liquid crystals featuring rod-like calamitic mesophases were described by Bruce and coworkers using substituted 5,15-di(phenyl) zinc porphyrin complexes as the basic molecular building block.The first materials... 

In a very recent study we examined theoretically the structure of water inside the water cylinder of inverse hexagonal mesophase (Hu) of monoolein (GMO). using methods of Molecular Dynamics. Due to the complex geometry of the system, a novel method for obtaining the distribution of water at the initial moment of calculation process is developed and applied. The initial density of water was obtained by fitting the final results within predictor-corrector scheme. 

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