Uniaxial alignment

Fig. 9. Photograph of a dispersion of particles in a gel. The dark parts represent the particles aligned uniaxially...

Spiropyrans are an important class of materials that show interesting properties such as photochromism and acidichromism. Similar to azo compounds, photoirradiation or the addition of acidic molecules to spiropyrans lead to drastic changes in physical and chemical properties due to spiro-merocyanine isomerization. Hexagonal columnar LC complexes of a spiropyran derivative with 4-methylbenzenesulfonic acid were formed due to the acid-induced spiro-merocyanine isomerization [100], The columnar LC mixture aligned uniaxially on a substrate can serve as one-dimensional ion conductors. When poly(styrenesulfonate) was employed as a complexing agent for spiropyran, no mesophase was observed. 

Ligament/tendon -Tension -Elasticity -Anisotropic, aligned uniaxially Ultimate stress = 50-150 MPa -Tensile modulus = 1.2-1.8 GPa... 

For amorphous systems with cylindrical symmetry, such as aligned uniaxial nematic liquid crystals or oriented amorphous polymers, the equivalent of the radial distribution function is the cylindrical distribution function (CDF). This function can be written as [2]... 

If a liquid crystalline material (polymeric or of low molar mass) is partially aligned (uniaxially) by the action of an aligning field (electric or magnetic) then a director order parameter may be defined as... 

As shown in Fig. 3.4 stress-strain tests on uniaxially aligned fibre composites show that their behaviour lies somewhere between that of the fibres and that of the matrix. In regard to the strength of the composite, Ocu, the rule of mixtures has to be modified to relate to the matrix stress, o at the fracture strain of the fibres rather than the ultimate tensile strength, o u for the matrix. 

The ultimate tensile strength of a uniaxially aligned fiber-reinforced composite is given to reasonable accuracy by the rule of mixtures relation ... 

Results of uniaxial strain static and gas gun compression tests on syntactic foam have been conducted. The foam was buoyant and composed of hollow glass microspheres (average diameter 100 microns) embedded in an epoxy plastic. Static testing consists of compressing a 0.25 cm x 2.5 cm dia. wafer between carefully aligned 2.5 cm dia. steel pistons. Lateral expansion of the wafer is... 

Kimira, T, Yoshino, M., Yamane, T, Yamato, M. andTobita, M. (2004) Uniaxial alignment of the smallest diamagnetic susceptibility axis using time-dependent magnetic fields. Langmuir, 20, 5669-5672. 

For oriented systems, the determination of molecular conformation is a complex problem because Raman spectra contain signals inherently due to both molecular conformation and orientation. To extract only the information relative to the conformation, one has to calculate a spectrum that is independent of orientation, in a similar way to the A0 structural absorbance of IR spectroscopy (Section 4). Frisk et al. [57] have shown that for a uniaxial sample aligned along the Z-axis, a spectrum independent of orientation (so-called isotropic spectrum), fso, can be calculated from the following linear combination of four polarized spectra [57]... 

The most common examples of uniaxially oriented materials include fibers, films, and sheets hot-stretched in one direction and composites containing fibers all aligned in one direction. Some injection-molded objects are also primarily uniaxially oriented, but most injection-molded objects have a complex anisotropy that varies from point to point and is a combination of uniaxial and biaxial orientation. 

IR absorption and Raman spectroscopy are also well suited to the application of uniaxial stress techniques. Stress-induced splittings of the vibrational bands give information about the symmetry of the defect. In favorable cases, it has been possible to determine the kinetics of the H motion between equivalent sites around an impurity from a study of the alignment of the H-related complexes that can be induced by stress. 

Figure 7.13 Chiral molecule prevents the parallel alignment of two adjacent solvent molecules (idealized as uniaxial rodlike objects).

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