Anisotropy ordered structures

In crystals with the LI2 structure (the fcc-based ordered structure), there exist three independent elastic constants-in the contracted notation, Cn, C12 and 044. A set of three independent ab initio total-energy calculations (i.e. total energy as a function of strain) is required to determine these elastic constants. We have determined the bulk modulus, Cii, and C44 from distortion energies associated with uniform hydrostatic pressure, uniaxial strain and pure shear strain, respectively. The shear moduli for the 001 plane along the [100] direction and for the 110 plane along the [110] direction, are G ooi = G44 and G no = (Cu — G12), respectively. The shear anisotropy factor, A = provides a measure of the degree of anisotropy of the electronic charge... 

The macroscopic design of CNT materials is an important factor regarding possible applications. Due to their anisotropy (see Section 1.3), the respective orientation and ordered structure can strongly affect the macroscopic properties of CNTs. Numerous attempts have been made in this direction, including different kinds of aligned CNTs [120] CNT carpets [121], films [122,123] and fibers [124]. Of these, this chapter will only focus on the latter. 

The structural anisotropy in crystalline or structurally ordered BPDA-PFMB films was studied in this laboratory with wide-angle X-ray diffraction (WAXD) methods. In brief, WAXD experiments were designed to examine both the reflection and transmission modes of thin-fihn samples. In addition, uniaxially oriented polyimide fiber WAXD patterns were obtained to aid in the identification of the film structure. The film WAXD pattern obtained from the reflection mode corresponded well to the fiber pattern scanned along the equatorial direction (Figure 16.3), " which indicates that the reflection mode pattern represents the (hkQ) diffractions. On the other hand, as shown in Figure 16.4, the (001) diffractions were predominant in the film WAXD pattern obtained via the transmission mode. This pattern corresponded to the fiber pattern scanned along the meridian direction. These experimental observations clearly indicate that the c-axes of the crystals are preferentially oriented parallel to the film surface however, within the film, they are randomly oriented. 4.2 5 j( should be pointed out that the WAXD experiments are only sensitive to crystalline or ordered structures in polyimide films. They do not provide any information on the amorphous regions. 

The properties of ordered structures in block copolymer melts have yet to be fully exploited, but the structural and rheological anisotropy is likely to lead to applications not all of which can be envisaged yet. The precision self-assembly of block copolymers into ordered structures for thin film and interfacial applications has enormous potential. Other applications such as nanoscale templates, membranes and filters could exploit the self-assembly of block copolymers into domains with periods 10-100 nm. The possibilities are limited only by the molecular engineer s imagination. 

Among the thiocyanates another order-disorder phase transition is possible. This involves a transition from an ordered structure similar to potassium thiocyanate to a disordered structure isostructural with potassium cyanate. This has been observed in potassium thiocyanate at 145 °C but has not been observed up to 300 °C in the nearly isostructural sodium salt. Iqbd (41) has suggested an explanation for this behaviour in terms of the greater anisotropy of the inter-ionic interaction potential in potassium thiocyanate compared with the sodium salt. 

Orientational order plays an important role in solid polymers. It is often induced by industrial processing, for example in fibers and injection- or compression-modulated parts. In polymers with liquid-crystalline properties of the melt or solution, the anisotropies generated by the flow pattern are particularly pronounced. In order to improve the mechanical properties of polymer fibers or films, the degree of orientation is intentionally enhanced by drawing. At the same time, anisotropy of mechanical properties can result in low tolerance to unfavourably directed loads. In many liquid-crystalline polymers, in the mesophase near the transition to the isotropic phase, electric or magnetic fields can induce macroscopic orientational order [1]. Natural polymers such as silk protein fibers, which are biosynthesized and spun under biological condition, also have good mechanical properties because of their ordered structure [2]. 

UP-ThP Lam and Aldred (1974) describe the rather divers earlier measurements. There is agreement that stable antiferromagnetic order remains for concentrations up to 32% ThP. The Neel temperature and the paramagnetic Curie temperature decrease systematically. No information on anisotropy, spin structures or ordered moments is available. 

Directionality in stacked complexes. Stacking interactions are a major determinant of NA stability, but act also to stabilize a diversity of ordered structures. We have considered a representative stacked dimer of formamide and rotated step-wise the second monomer with respect to the first around the z-axis [105]. The curve of Emtp augmented with Epen is virtually superimposable over that of Ec (Fig. 1.3a. The curve of E ep matches well that of Eexch with only a small indentation at the most repulsive point (Fig. 1.3b. The parallelism of AE (SIBFA) with AE(HF) is evidenced in Fig. 1.3c. Extensions are presently underway to NA bases, and are carried out at both uncorrelated and correlated levels, and they appear conclusive as well (Gresh et al. J Phys Chem B, 2015, 119, 9477). Such results suggest that the anisotropy of AE(QC) in stacked complexes can be reliably accounted for in the context of the SIBFA procedure. 

Tak] Takahashi, M., Arai, H., Tanaka, T, Wakiyama, T., Magnetocrystalline Anisotropy for Fe-Al-Si (SENDUST) Single-Crystals wifli DO3 Ordered Structure , IEEE Trans. Magnetics, 22, 638—640 (1986) (Experimental, 7)... 

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