Molecular orientation homogeneous

Nucleation can occur either homogeneously or heterogeneously. Homogeneous nucleation occurs when random molecular motion in the molten state results in the alignment of a sufficient number of chain segments to form a stable ordered phase, known as a nucleus. The minimum number of unit cells required to form a stable nucleus decreases as the temperature falls. Thus, the rate of nucleation increases as the temperature of the polymer decreases. The rate of homogeneous nucleation also increases as molecular orientation in the molten polymer increases. This is because the entropy difference between the molten and crystalline states diminishes as molecular alignment in the molten state increases. 

Various inert compounds such as fatty acids, fatty alcohols, and lipids behave as two-dimensional diluents for Chi monolayers and lead to the formation of homogeneously mixed monolayers (20). These diluents have facilitated the study of Chl-Chl energy transfer within a two-dimensional plane as a function of the intermo-lecular Chi separation (26,27). In sufficiently dilute mixed monolayers, a majority of the Chi molecules are thought to exist in the monomeric state, with their mutual aggregations effectively suppressed within the geometrically controlled, ordered configuration. Multilayers (built-up monolayers) of Chi a have also been studied (23) and utilized for photovoltaic studies (see the next section). The molecular orientation in such Chi a multilayers has been ascertained from the observed dichroism in spectropolarization measurements with respect to absorption (23) and emission (28). 

Frozen-in stresses due to molecular orientation may also be measured by this technique, since oriented polymers shrink rapidly above the softening temperature. Non-homogeneously oriented parts cause deformations. 

The spherical DFT approach accompanies the approximation of real molecules as radially symmetric particles and assumes that the anisotropic relations can be treat as quasi-radially symmetrically replacing it by its non-weighted orientation average. The results show that the legitimacy of this approximation becomes questionable, if the homogeneous molecular fluid changes to the inhomogeneous fluid with anisotropically distributed molecular orientations. 

In a homogeneous liquid or gas, the molecules are randomly orientated, and we must consider the polarizability components averaged over all molecular orientations. The results are expressed in terms of two quantities a mean value) and y (anisotropy) ... 

The molecular orientation of the polymer matrix is described by means of a vector field n(x,y,z), with n being the unit vector (director) oriented along the mean molecular orientation direction. The molecular orientation of uniaxially drawn homogeneous polymers might be approximated, if one neglects the influence of the outer shape of the sample, to the cylindrical symmetry described by the orientation distribution function of the form ... 

The mixture was injected into a homogeneous glass cell with 25-pm cell gap to obtain a planar molecular orientation. The longer edge of the reflection band of the Ch LC was adjusted to the emission maximum of DCM as shown in Fig. 10.28... 

Optical microscopy techniques can also be applied to packaging failure problems. Sections can be taken through a heat seal region to establish the integrity of the seal. Molecular orientation, melt flow, blend homogeneity, and crystallinity can be observed that can reveal the cause of stress cracking and other types of packaging failures. 

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