Apparent birefringence

Photograph 6-1 One s method for apparent birefringence of alite in powder mount. Crystal length-to-width ratio = approximately 2 1. Ono measures particle width. Other observers, the present writer included, measure crystal width. (S A6616)... 

One of the principal difficulties in the determination of apparent birefringence by powder mount is finding proper crystals, those with relatively bright interference colors and length to width ratios of approximately two. Extreme difficulty in satisfying the ratio requirement may, in itself, be indicative of burning conditions such that the desired crystal development was inhibited. 

The problem of measurement of crystal thickness (t) for the determination of alite birefringence in powder mounts has been the subject of much discussion. Prout (oral communication, 1984) finds that the thick ness can be approximated by the equation (length + width)/2, giving a reasonable apparent birefringence. 

During the studies of phase behaviour two types of liquid crystalline phases were identified. LC material was viscous and exhibited intense "white" birefingence. material was apparently homogeneous but of low viscosity and exhibited "multi-coloured" birefringence. The liquid crystalline phases observed in the equilibrium studies of surfactant concentrations up to 25 are unlikely to take part in the self-emulsification process due to the presence of two-phase regions between L2 and liquid crystalline phases however, LC material may account for the improved stability of emulsions formed by 25 surfactant systems (Table II). Figure 4c indicates that by increasing the surfactant concentration to 30 the... 

The rotational diffusion constant in water at 25° and neutral pH as measured by electric birefringence (258) is 230 X 105 sec-1 or 0.73 X HT8 sec as a relaxation time. For a hydrodynamic ellipsoid of dimensions 66 X 22 A and a molecular weight of 14,000, the calculated relaxation tilde is 0.72 X 10-8 sec. However, the apparent asymmetry of the molecule from the X-ray structure corresponds to an axial ratio of no more than 2 1 rather than 3 1. 

Stress Birefringence. Confirmation of the multiphase nature of the polyblends described may be obtained by stress-optical measurements. Since this technique apparently has not been used before to demonstrate incompatibility in polyblends, a brief description is given of the rationale behind the method. 

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