Negative birefringence film

Unstretched PPX films exhibit an inherent negative birefringence, the optical axis of which is perpendicular to the plane of the film. The refractive index along the optical axis is lower than the refractive index observed in the plane of the film, the difference being = —0.075 0.001 (42). Where... 

There is an almost infinite potential to combine different kinds of compensation films in many different ways to achieve a given effect, e.g. compensation layers of negative birefringence with the optical axes in the plane of the cell situated on either side of a TN-LCD improve the viewing angle dependence in the horizontal plane, but not in the vertical plane. However, if the optical axis of the compensation layer is tilted with respect to the plane of the cell, then superior optical properties in the vertical direction are also achieved. Compen-... 

Crosspolarized photomicrographs of PEO 1, EO-Is-EO 2, EO-Is-EO 3, and EO-Is-EO 4 films cast from 1% benzene solutions at 30° C are presented in Figure 1. The spherulitic texture with negative birefringence became less perfect and led to a less clear Maltese cross as the fraction of amorphous Is segment increased. When the EO fraction constituted less than 50%, the texture was not clearly resolved by light microscopy. 

As the stress of the film is increased further, the increase in negative birefringence An comes slower as a result of the development of positive birefringence. 

H. Mori, Y. Itoh, Y. Nishima, et al.. Performance of a novel optical compensation film based on negative birefringence of diseotie eompound for wide-view-angle twisted-nematic liquid crystal displays, Jpru J of Appl. Phys., 36, 143 (1997). 

Fig. 3.14 Two images of a thin i melt-cast film of polycaprolactone. As in Fig. 3.13, the region is 200 x 250/zm, the left-hand image was taken under crossed polars and for the right-hand image, a first order red plate was also used. The spherulites in this material are much less regular, and some show colors under crossed polars. The first order red plate image can still show that the spherulites are negatively birefringent.

The wavelength dispersion of the out-of-plane birefringence of the samples is shown in Fig. 9.9. The solution-cast films, including CTA (butyryl content is zero], show positive birefringence although CTA shows negative In-plane birefringence. The out-of-plane... 

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