Quasi-hexagonal symmetry

An example of such order is shown by the hexagonal symmetry of SBS as revealed by LAXD, electron microscopy and mechanical measurements. In composite materials the choice of phase is at the disposal of the material designer and the phase lattice and phase geometry may be chosen to optimise desired properties of the material. The reinforcing phase is usually regarded elastically as an inclusion in a matrix of the material to be reinforced. In most cases the inclusions do not occupy exactly periodic positions in the host phase so that quasi-hexagonal or quasi-cubic structure is obtained rather than, as in the copolymers, a nearly perfect ordered structure. 

Table 1 compares the molecular array and orientation parameters thus obtained for the three adsorption systems examined here. AU the three adlayers examined here appears to form a well-ordered (quasi-)hexagonal array on the two zeolite surfaces. Since the surface symmetry of either zeolite (010) surfaces are not hexagonal, this hexagonal... 

Recently it was shown [156] that in the system C12E8-water, upon cooling samples containing less than 39% surfactant, a new type of nonbirefringent hexagonal micellar phase was observed. It had two quasi-spherical micelles per unit cell of hexagonal symmetry. 

Liu [314] has pointed out that a more general concept of biaxial nematics should include triclinic, hexagonal, cubic and even quasi-isotropic symmetry. He gives the number of independent elastic constants for triclinic systems as 36 and that for quasi-isotropic systems as 2. A discussion of elastic theory for nematics having arbitrary point synunetry groups has also been given by Fel [324]. 

Because of the existence of the quasi-hex-agonal lattice in the tilted hexatic phase, there are three possible molecular tilt directions, The molecular tilt points towards the nearest neighbor for the SmI phase, towards the next nearest neighbor for the SmF phase, and towards an intermediate site for the novel SmL phase (see Fig. 1). Thus the former two have a higher symmetry than the SmL phase, which was first discovered in a lyotropic liquid crystal system [87]. The most common tilted hexatic phases found in thermotropic liquid crystal compounds are SmI and SmF. As mentioned previously, the pseudo-hexagonal molecular arrangement which is the characteristic feature of the hexatic phase, was first identified for the SmI phase. 

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