Birefringence of a polymeric cholesteric liquid crystal measured by refractometry

Abstract

SynopsisThe Abbe refractometer provides a convenient way to measure the refractive indices and birefringence of polymeric liquid crystalline solutions. The cholesteric mesophase formed by (acetoxypropyl) cellulose and its solutions in dibutyl phthalate were examined at 26°C and 5OOC. The measured refractive indices were dependent on the direction of shear when the polymer was applied to the refractometer plates. The initial shear-induced nematic-like order relaxed slowly to the equilibrium planar cholesteric structure. The refractive index for the isotropic solutions and the two refractive indices for the anisotropic solutions all varied linearly with polymer concentration, and the width of the intermediate two-phase region was readily determined. The changes in refractive index with polymer concentration and with orientation on the refractometer plate were rationalized with E simple model of the cellulosic mesophase, and an order parameter of 0.7 was estimated. The layer birefringence calculated from optical rotatory dispersion measurements of the cholesteric reflection band intensity was in good agreement with the birefringence measurements.

Synthesis, Characterization, and Mesophase Formation of Phenylacetoxy Cellulose and Its Halogenated Derivatives

“…The positive ∆n indicates that the refractive index of axial direction n | is smaller than that of tangential direction n ⊥ . 20 The larger refractive index in the tangential direction may be due to the larger polarizability of the substitution groups as compared to the smaller refractive index in the axial direction caused by the cellulose backbone. 24 The critical concentrations for phase separation of lyotropic phenylacetoxy cellulose solutions were determined by the chiral nematic birefringence.…”

“…The sandwiched samples were relaxed for at least 3 days before microscopic observation. The birefringence of the liquid crystalline solutions was measured at room temperature (23 °C) using the procedure of Laivins and Grey 20 and an Abbe Refractometer (Milton Roy Inc.).…”

Preparation and chiroptical properties of tritylated cellulose derivatives

“…The two refractive indices nx and nz (across and normal to the refractometer plate, respectively) were easily distinguishable with a polarizing filter. 28 The values for nx and nz were measured with the privileged direction of the polarizer parallel and perpendicular to the line separating the two fields, respectively. The measured birefringence (rc* -nz) was found to remain relatively constant at 0.0035 ± 0.0002 over the observed temperature range.…”

“…The magnitude of the birefringence was observed to increase with polymer concentration in agreement with results obtained for other cellulose-based mesophases. 28,33,34 The concentration dependence of the pitch is shown in Figure 6. The pitch was observed to decrease in a nonlinear fashion as the polymer concentration was increased from 55 to 82 vol % TBzC.…”

Effect of molecular weight on the birefringence of lyotropic liquid crystalline ethyl cellulose and hydroxypropyl cellulose

“…This suggests there is (2) An increased with decreasing temperature and approached a constant value a t a relatively (3) The behaviors described in (1) and (2) …”