LIFCHITZ INVARIANT IN THE ELASTIC ENERGY DENSITY FOR LANGMUIR-BLODGETT-FILMS

By means of a pseudomolecular model the elastic constant connected to the Lifchitz invariant is evaluated for Langmuir-Blodgett films. Our a nalysis shows that this term exists whenever the intermolecular forces responsible for the nematic-like order of the Langmuir-Blodgett film depend not only on the relative orientation of the rod-like molecules forming the film. The peculiarities of the Lifchitz invariant are disc ussed in the framework of the usual elastic theory.