Birefringent layer formation

Birefringence itself can provide a novel mechanistic tool. Reduction in the symmetry of tetragonal crystals due to selective formation of product in one orientation can be observed with a polarizing microscope, even when neither starting material nor product has an absorption in the visible spectrum. This technique has been used to show confinement of reaction within individual lamellae of a layered crystal [40]. By using dispersion rather than absorption, this technique extends the range of reactions that can be studied optically. 

Before joining the longitudinal wall of the mother cell, the cell plate becomes weakly birefringent, and two narrow, bright layers can be observed on both sides of the central lamella. The growing cell-plate thus consists of three layers already, namely, the middle lamella in the center and tiie two primary walls of fiiture daughter cells that are being developed as the outer layers. The formation of cell plate is shown in Fig. 19. 

Relatively high dichroic ratio up to 2.3 due to geometry of the molecule (high aspect ratio of Direct Red 80) has been achieved (Advincula et al., 2003). To manufacture these films with PD ADM AC of ca. 100-nm thickness, 100 layers were necessary. Less effective photoorientation of spin-coated and LbL films with other polyelectrolyte (PAH, PEI) was attributed to specific formation of J-aggregates in LbL films. In the LbL films produced from chitosan and Sunset Yellow (dos Santos et al., 2002), spontaneous birefringence of 0.04 for the film of 300-nm thickness was observed however, the value was not affected by the light. This fact underlines the importance of selection of dye and polyelectrolyte. 

Carboxymethyl Cellulose (CMC) -In vivo cellulose ribbon formation prevented normal fasciation of fibril bundles into a typical ribbon -Thinner ribbon width and smaller crystallite fibril size -Aggregates and pellicle show birefringence, and contain crossed, superimposed layers of cellulose fibrils oriented in parallel -Less resistant to stress... 

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