Specific layer birefringence

Table II. Specific Layer Birefringence Cellulose/NH3/NH4SCN+ of ...

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. 

The SmA phase has the same symmetry and the same dielectric ellipsoid as in nematics, therefore, everything said above about the birefringence and dichroism is valid for the SmA phase. However, due to specific elastic properties of the layered structure, the director fluctuations are strongly quenched, and the SmA preparations are much more transparent than the nematic ones. This is related to specific elastic properties of the lamellar SmA phase [14]. 

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