CELL THICKNESS EFFECTS IN THE DETERMINATION OF ELASTIC-CONSTANT RATIOS BY OBSERVING RAYLEIGH LIGHT SCATTERED INTENSITY

The effects of the finite scattering volume on the values of elastic constant ratios determined have been studied by computer simulation. The errors in the simulated values of K1/K2 and K3/K2 are dependent on the position of the starting angle of the scan. The error is greatest for thinner cells (almost-equal-to 7-mu-m) and in the angular regions where the geometrical factor G(m) introduced by de Gennes, or a component of the scattering vector q becomes zero, i.e. for external scattering angles approximately less than 10-degrees and those between approximately 20-degrees and 60-degrees, depending on the scattering geometry used. The approximation introduced by van der Meulen and Zijlstra in defining the orthogonal base system (e1, e2, e3) has also been discussed; it is inappropriate in thin cells to use the scattering vector q instead of the wave vector k(l) of the director fluctuations when determining K1/K2.