Lists
Lists
Champion, J. V. (1958) An investigation of streaming birefringence in pure liquids. Doctoral thesis, Sir John Cass College.
Using the theory of Eisenschitz (1949) on the steady non-uniform state of a liquid, a magnitude has been calculated for the anisotropy of flow due to distortion of the radial distribition function. The optical anisotropy is obtained by considering the variation of the polarisation due to the non-uniformly distributed induced dipoles (Bragg (1924)). The Maxwell constant (M = 1.46 x 1012sec.) corresponding to ∆n = 7.3 x 10-8, is obtained for chloroform and a value of the same order of magnitude is expected for a similar molecule (carbon tetrachloride).
The calculation shows that the main contribution to the anisotropy arises from small values of the range r, and the magnitude of the anisotropy is independent of the precise way in which the distortion decreases at large distances. This implies that the 'strong' condition of Eisenschitz cannot be supported by an appeal to the isotropy of flow.
In order to test this calculation experimentally, a coaxial cylinder apparatus suitable for the measurement of the streaming birefringence of pure liquids at very high velocity gradients (50,000 sec-1) has been built. A new experimental technique for measuring a weak birefringence was developed. The liquid was sheared for the shortest time possible (in the order of 10 sec.) so that the heating effects within the liquid were negligibly small. Measurements have been made on ethyl cinnamate, chloroform and carbon tetrachloride and, in the latter case (a tetrahedral molecule), there is a favourable agreement between experiment and theory. The Maxwell constants for chloroform and carbon tetrachloride have been determined for the first time.
 |
View Item |