Crystals molecular alignments

A glass substrate, which has a transparent common electrode on its inner surface, is placed facing this matrix pixel substrate as shown in Fig. 7 (b). A liquid crystal molecular alignment layer is provided on the... 

Also the above-described SmQ phase was object of molecular simulation studies by using the molecule shown in Fig. 10.42 [99]. Figure 10.43 shows the structure of the SmQ phase, which is also known as the r l phase. This structure is based on a model according to Levelut et al. (Fig. 10.40 in [100]), in which the local liquid crystal molecular alignment direction is tilted in respect to the layers of smectic blocks. In the case of a 45° tilt, this leads to a cubic phase with a threefold symmetry. 

The response of liquid crystal molecular orientation to an electric field is another major characteristic utilised for many years in industrial applications [44] and more recently in studies of electrically-induced phase transitions [45]. The ability of the director to align along an external field again results from the electronic structure of the individual molecules. 

Molecular alignment in the monomer crystals is controlled by several intermolecular interactions, such as strong and weak hydrogen bonds, leading to the formation of various types of stereoregular polymers via a topochemical polymerization process. This approach to the stereocontrol of polymers differs from other conventional ways in the control of the propagating chain end using catalysts or additives in solution polymerization. 

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. 

Crystals. In Section III.D, we noted that the photobehavior of molecules on the surface and in the interior of crystals need not be the same. In addition the arrangement and excited state energy of molecules at defect sites are often not the same as in the bulk of the crystal. Indeed, there are a number of examples wherein the stereochemistry of photoproducts cannot be predicted on the basis of the molecular alignment of molecules in the bulk of a crystal [214],... 

It is evident that two hydrogen bonds between adjacent molecules and the chirality of molecule contribute to one dimensional molecular alignment in spite of the strong dipole-dipole interactions and that -conjugated system of DAD molecule extend from amino groups to cyclobutenedione ring enhance second order nonlinearity of DAD molecular crystal. 

The half-widths of 37-39 and 78-88 Hz, respectively, for the crystalline and amorphous phases are significantly larger than 18 and 38 Hz for those of the bulk-crystallized linear polyethylene (cf. Table 1). This is caused by incorporation of minor ethyl branches. The molecular alignment in the crystalline phase is slightly disordered, and the molecular mobility in the amorphous phase will therefore be promoted. With broadening of the crystalline and amorphous resonances, the resonance of the interphase also widens in comparison to that of bulk-crystallized linear polyethylene samples. This shows that the molecular conformation is more widely distributed from partially ordered trans-rich, conformation to complete random conformation, characteristic as the transition phase from the crystalline to amorphous regions. 

FIGURE 7.15. Molecular structure of a peptide amphiphile that self-assembles into a cylindrical aggregate. The five key structural elements of die peptide are highlighted. The cylindrical aggregate assembles into fibers that template the mineralization of die hydroxapatite crystal. The c axis of the crystal is aligned with the long axis of... 

K. Hongladarom, W. R. Burghardt, S. G. Baek, S. Cementwala, and J. J. Magda, Molecular alignment of polymer liquid crystals in shear flows. I. Spectroscopic birefringence technique, steady-state orientation, and normal stress behavior in poly(benzyl glutamate) solutions, Macromolecules, 26, 772 (1993). 

The use of birefringence to determine the behavior of 5( 7) is a natural choice since the principal characteristic of the nematic phase is optical birefringence i.e., the refractive index differs for light polarized parallel (/ n) or perpendicular (%) to the axis of molecular alignment. Eor a nematic liquid crystal, the director n specifies this optical z axis and / n = and = Dg are called the extraordinary and ordinary refractive indices, respectively. In general, rig > rig and the difference is the refractive index anisotropy (birefringence)... 

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