RESUMO
The symmetry of the cholesteric uniform lying helix (ULH) structure, where the helix axis is aligned in a single direction parallel to the device substrates, is not compatible with a uniform surface alignment and an unwinding of the helical structure is expected at the interface. Fluorescence confocal polarizing microscopy experiments are performed on the interface between a bulk ULH and a uniform aligning surface (for both planar and homeotropic alignments). The results are analyzed in the framework of a finite difference numerical simulation based on the Frank elastic distortion, to determine relevant director structures. An optical model is introduced to predict three-dimensional fluorescence profiles for the structures. Comparison of experimental and theoretical results shows that the equilibrium structure of the system involves a continuous unwinding of the helix close to the surface.
RESUMO
In this article we demonstrate the use of liquid crystal technologies in the determination of enantiomeric excess and in the sensing of molecular chirality, particularly at values near to zero. We use this technique to investigate the optical purities of the commercially available chiral natural product, menthol, and in the investigation of the optical activity of racemic ibuprofen.
