Surface‐induced ordering of a liquid crystal in the isotropic phase. II. 4‐methoxybenzylidene‐4′‐n‐butylaniline (MBBA)

The boundary order parameter of the liquid crystal 4‐methoxybenzylidene‐4′‐n‐butylaniline (MBBA) in the isotropic phase has been deduced for several surface treatments by measuring the surface‐induced pretransitional birefringence. Results for the silane surface coupling agent, methyl‐3‐aminopropyltrimethoxy‐silane (MAP) were particularly interesting, indicating a negative surface order parameter. An analytic expression for the temperature‐dependent birefringence is derived from Landau’s expanison in the order parameter. This expression shows that the value of the boundary order parameter determines the absolute minimum isotroic phase temperature.