Phase transitions in a cholesteric close to a disordering surface

The thermodynamic behaviour of a semi-infinite cholesteric sample close to a disordering surface is analyzed within the frame of the Landau-Ginzburg-d e Gennes theory. In particular, the effect of the boundary on the field-ind uced cholesteric-nematic phase transition is considered. The appearance of a nematic layer on the top of the cholesteric bulk phase is predicted and a n experiment which could possibly demonstrate this phenomenon is proposed.