DETECTION OF PHASE-TRANSITIONS IN LIQUID-CRYSTALS ON A WATER-SURFACE BY A MAXWELL DISPLACEMENT CURRENT-MEASURING TECHNIQUE

The phase transitions of Langmuir films of liquid-crystal 4-cyano-4′-5-alkyl-biphenyl (5CB), 4-cyano-4′-7-alkyl-biphenyl (7CB), 4-cyano-4′-8-alkyl-biphenyl (8CB), and 4-cyano-4′-10-alkyl- biphenyl (10CB) were investigated by a Maxwell displacement current (MDC)-measuring technique. A weak first-order phase transition of the orientation of LC molecules from the isotropic phase to the polar one was clearly detected by compressing the film in the range of immeasurably low surface pressure by means of the technique. For further compression, a first-order phase transition between a stable monolayer phase and a stable three-layer phase of the liquid crystal film was detected. The result shows that the MDC-measuring technique is useful in the detection of phase transitions over the entire range of molecule areas. © 1995 American Institute of Physics.