Birefringence structural

By optical microscopy (OM), birefringent structures are observed in semicrystalline polymers, characterized by "Maltese-crosses" under crossed polars as seen in Figure 6. As these structures grow symmetrically in three dimensions... 

Examination of thin sections of semicrystalline polymers reveals that the crystallites themselves are not arranged randomly, but form regular birefringent structures with circular symmetry. These structures, which exhibit a characteristic Maltese cross-optical extinction pattern, are called spherulites. Although spherulites are characteristic of crystalline polymers, they have also been observed to form in low-molar-mass compoimds that are crystallized from highly viscous media. 

Figure S. Birefringence of copolymers with 2 positive or 2 negative birefringent structure units...

We assume that birefringence can arise from two sources a crystallization (or ordering phenomenon) from the amorphous phase to give birefringent structures and an orienting of macromolec-ular chains either in the crystalline or the amorphous phases. 

In general, the surfactant formulations used for enhanced oil recovery contain a short chain alcohol. The addition of alcohol can influence the viscosity, IFT and birefringent structures of micellar solutions as well as coalescence rate of oil ganglia. The present paper reports the effect of addition of isobutanol to a dilute petroleum sulfonate (< 0.1% cone) solution on IFT, surface shear viscosity, surfactant partitioning, the rate of change of IFT (or flattening time) of oil drops in surfactant solutions and oil displacement efficiency. The two surfactant systems chosen for this study indeed exhibited ultralow IFT under appropriate conditions of salinity, surfactant concentration and oil chain length (11,15,19). 

Fully developed spherulites are usually microscopic and exhibit radial symmetry [19,35-38] a schematic of a birefringent structure of a spherulite is shown in Figure 16.2 [28]. Nudeation and growth are the key mechanisms of spherulite formation [30,32,34,39,40]. Internal fluctuations in the system cause homogeneous... 

Figure 16.2 Schematic representation of the birefringence structure of spherulites. The high-power image shows the helical chains stacked together in a well-ordered lattice of crystalline...

Figure 11.6 Schematic illustration of the images of birefringent structures of different orientation with respect to the polarizer (P)/analyser (A) pair. Top crossed polarizers only. Bottom crossed polarizers with an inserted lambda plate.

The first octahedral metallomesogen was an iron(III) tris-diketonate, 29, which showed a birefringent structure and endothermic transitions but the mesophase has not been defined [74]. 

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