Abstract
We have carried out a high-resolution x-ray study of the mass-density fluctuations and a light-scattering study of the bend-mode-director fluctuations associated with the nematic-smectic- phase transition in 4-cyano-4′-octylbiphenyl (8CB). This phase transition is found to be nearly second order with a first-order temperature jump of less than 10 mK. The peak scattering intensity, , with , where is the layer spacing, and the longitudinal correlation length, , exhibit single power-law divergences for with critical exponents of and , respectively. These exponents agree within the errors with the predicted , values appropriate to de Gennes' superconductor analogue model. The ratio of the longitudinal to transverse correlation lengths, , increases gradually with decreasing reduced temperature, changing by a factor of 2.6 over the above temperature range. This corresponds to an effective exponent difference . The bend mode elastic constant , which is predicted to have a divergent contribution , exhibits single power law behavior for , with in reasonable agreement with the x-ray results. The predicted amplitude is, however, wrong by a factor of four. Measurements of , the layer compressibility coefficient in the smectic- phase, yield with , in agreement with previous experiments in N--cyanobenzylidene--octyloxyanilene (CBOOA) and octyloxycyanobenzylidene (80CB), but in marked disagreement with the superconducting analogue model which predicts .
- Received 12 June 1978
DOI:https://doi.org/10.1103/PhysRevB.19.1657
©1979 American Physical Society