Amorphous organic matrix

Since the dipoles of chromophore molecules are randomly distributed in an inert organic matrix in amorphous PR materials, the material is centrosymmet-ric and no second-order optical nonlinearity can be observed. However, in the presence of a dc external field, the dipole molecules tend to be aligned along the direction of the field and the bulk properties become asymmetric. Under the assumption that the interaction between the molecular dipoles is negligible compared to the interaction between the dipoles and the external poling field (oriented gas model), the linear anisotropy induced by the external field along Z axis at weak poling field limit (pE/ksT <[Pg.276]

Electron microscopic studies further substantiate the presence of highly-ordered macromolecular structures with the corneum cells (24, 31). The fibrous keratin structure has been described as low-density filaments, low in sulfur but embedded in a dense sulfur-rich amorphous interfilamentous matrix. The keratin fibrils organize into lipid-covered bundles preferentially oriented in the longitudinal plane of the acutely flattened cell (16). These filaments terminate at the periphery of the cell... 

Figure 5. The amorphous structure of an organic matrix leads to a Gaussian density of states for the HOMO of the donor transport matrix. Some of the donors will have a relatively small oxidation potential (in the shaded region) and these sites are likely to experience a potential barrier inhibiting charge hopping to adjacent sites of higher oxidation potential. A hole may in this way become an immobilized cation.

Note that if precipitation proceeds via pathway B of Fig. 3.9, and the final mineral is crystalline, then nucleation vnll not be a determining factor in the crystallographic structure of the final mineral since the initial phase is amorphous. In such cases mineral structure will be dependent on biological control (chemical and/or organic matrix-mediated) over mineral growth and phase-transformation processes. 

Fig. 8 Nacre retrosythesized in the insoluble organic matrix of a Haliotis laevigata shell via amorphous precursor particles. The upper pictures compare the natural and synthetic nacre. The lower pictures show the corresponding transmission electron micrographs (TEM) of microtomed samples a synthetic nacre, b synthetic nacre in higher zoom, c electron diffraction pattern taken in this region and showing an almost single crystalline calcite domain, and d thin cut of natural nacre. Reprinted from [132] with permission of the American Chemical Society...

Organic matrix containing amorphous calcium phosphate... 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. 

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