The small magnitude of (${\mathit{T}}_{\mathit{c}}$-${\mathit{T}}^{\mathrm{*}}$)/${\mathit{T}}_{\mathit{c}}$, where ${\mathit{T}}_{\mathit{c}}$ is the nematic-isotropic phase transition temperature and ${\mathit{T}}^{\mathrm{*}}$ denotes the virtual transition temperature, has been a long-standing puzzle in the physics of liquid crystals. We show that by extending the mean field theory to include the isotropic, density-dependent component of the molecular interaction the magnitudes of both (${\mathit{T}}_{\mathit{c}}$-${\mathit{T}}^{\mathrm{*}}$)/${\mathit{T}}_{\mathit{c}}$ and the density change at the transition automatically become in accord with the experimental values. In addition, the theory yields a value of ${\mathit{dT}}_{\mathit{c}}$/dp, where p denotes pressure, that is on the same order as the experiment.

• Received 30 October 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.1271