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P‐108: Birefringence Dispersion of Polymer Films As Applied to Optical Compensation in LCD
Author(s) -
Greener Jehuda,
Rao YuanQiao,
Elman James F.
Publication year - 2007
Publication title -
sid symposium digest of technical papers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.351
H-Index - 44
eISSN - 2168-0159
pISSN - 0097-966X
DOI - 10.1889/1.2785375
Subject(s) - birefringence , dispersion (optics) , polymer , materials science , optics , compensation (psychology) , liquid crystal , liquid crystal display , composite material , optoelectronics , physics , psychology , psychoanalysis
Minimizing color shift effects in a liquid crystal display (LCD) requires close attention to the optical dispersion of compensation layers used to increase the contrast ratio and viewing angle of the display. This paper describes our attempt to systematize and characterize the birefringence dispersion of solvent‐cast polymer films and relate it to the “native” out‐of‐plane birefringence (Δn th ) of the polymer and its structure. Results for a wide range of polymers show general correlation between the dispersion parameter DP Δn [≡Δn(450)/Δn(590)] and Δn th . for all positively birefringent polymers, DP Δn is always > 1, suggesting “normal” dispersion at any level of Δn th , while for negatively birefringent polymers DP Δn > 1 only when |Δn th | > ∼0.003. Below this critical value, DP Δn < 1, i.e., the polymer is reverse‐dispersive. The results are explained in terms of the Cauchy coefficients for the corresponding polymers, and they suggest that the dispersion of birefringence cannot be controlled independently of the birefringence of the polymer film.