Optical Properties of Nematic Poly-γ-Benzyl-L-Glutamate
Poly-γ-benzyl-L-glutamate (PBLG) in certain solvents adopts an α-helical conformation and thus geometrically resembles a long, rigid rod with side chains containing benzyl radicals extending latterally outwards along the rod axis. As the refractive indices parallel and perpendicular to the helical axis are different, a-lignment of the macromolecule results in optical birefringence, The effect is dramatically seen by simply allowing a PBLG solution to flow between crossed polars. The rod shaped macromolecules tend to conform with hydrodynamic flow lines, producing a birefringent solution of remarkable color (streaming birefringence). The PBLG molecule itself has a positive dielectric and diamagnetic aniso-tropy, with the components of the dielectric and magnetic susceptibility tensor parallel to the long molecular axis larger than those perpendicular. In the presence of an electric or magnetic field individual PBLG molecules will also tend to align themselves, in this case such that their long axes are parallel to the direction of imposed field.
KeywordsVortex Convection Petroleum Chloroform Polypeptide
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