Packing symmetry

The cubic packing symmetry of the spherical domains is often body-centered cubic (BCC) (Thomas et al, 1987 Almdal et al. 1993 Okamoto et al. 1994a Chu et al. 1995 Adams et al. 1996) and, when solvent is present, sometimes face-centered cubic (FCC) (McConnell et al. 1993). The BCC packing is characteristic of spheres that interact via... 

All the methods discussed here are designed for organic molecules and are only capable of generating the most common packing symmetries moreover, they only consider structures where there is only one independent molecule in the unit cell and only certain space groups. They should, nevertheless, be able to predict the vast majority of the organic crystal structures in the Cambridge Structural Database. 

The size of the colloidal particles ultimately determines the size of the resulting pores, and the geometry of the pore arrangement is essentially determined by the packing symmetry of the templating particles. Monodisperse... 

Molecules in a condensed phase are different from gas phase molecules in that they are restricted to a relatively fixed orientation. In crystalline phases, a regular molecular packing symmetry is established relative to the crystal axes while in amorphous materials, long-range... 

In order to improve the packing symmetry and reduce the defect concentration, many attempts were made to prepare monolayers or multilayers of near-monodis-perse nanoparticles. In a straightforward approach, monolayers could be prepared almost defect-free on a water surface, and transferred via microcontact printing onto solid substrates [86] (Figure 5.58). 

At present, eight different phases are known in banana compounds dependent on particular in-plane packing symmetry and they usually labelled as Bi, B2, -Bg, etc., counted from the isotropic phase [44]. Among them the B2 phase is especially interesting, because it has low viscosity and can easily be switched by an electric field with rather short switching times [45]. In fact, the B2 phase is basically a conglomerate of chiral and achiral antiferroelectric structures SmCAPA and SmCAPA mixed with some percentage of the two ferroelectric structures. 

These pioneering works were later extended by different research groups in order to optimize the control of the packing symmetry, which is of fundamental importance in the growth of PBGs. For this purpose, combination of convective or capillary-based assembly methods with topologically patterned substrates has been successfully implemented. ... 

Fig. 25.7 Schematic 2D model depicting the thermal transformation (A implies heating) of a herringbone packed symmetry) array of rotors to the orientationally disordered rotator phase at which point the ratio a/ b sin a) becomes exactly 5.

However, it should be noticed here that the introduction of chirality is one of the simplest ways to reduce the packing symmetry. The research of banana-shaped liquid crystal is actually bom from this fact. In other words, the attachment of a bent shape into a molecule could give rise to a smectic (Sm) stmcture which has the polar twofold axis along the bent direction and thus to ferroelectric and antiferro-electric Sm LCs without a chiral center. This was firstly suggested in the polymer molecules, successfully demonstrated in bent dimers and then in banana molecules. 

Figure 8.8 (Continued) (c) The distribution of the local orientation order parameter Qg shows the kinds of packing symmetries observed at various volume fractions, (d) Fraction of particles with hep and fee symmetry as a function of volume fraction. (Adapted from Panaitescu, A. et al., Phys. Rev. Lett., 108,108001, 2012.)...

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