FROM MONOMOLECULAR FILMS TO BULK LIQUID-CRYSTALS

Molecules forming thermotropic liquid crystal bulk phases, were investigated at the air-water interface. With nematic and smectic substances, compression of the film resulted in an increase of the lateral pressure, provided the molecules had an amphiphilic character. Two types of pi - A - diagrams were found for areas below a threshold value: (i) A single coexistence region (constant pressure at different areas) is obtained for molecules forming nematic liquid crystal bulk phases. The original monomolecular film grew in the third dimension to form a nematic liquid crystal at the interface. (ii) the pi-A-diagram showed several coexistence regions with constant pressures if the molecules had the capacity to form smectic bulk phases. The "collapses" were at areas in the relation 1 : 1/2 : 1/3 etc. suggesting that smectic layers have been formed. The aqueous subphase is found to make a large contribution to the latent heat. The initial layer (together with the subphase) is found to be of lower symmetry than the upper layer(s). The transition is first order at low temperature (< 30-degrees-C) and second order at high temperatures. Evidences are given for a smectic Shubnikov phase where the layer-to-layer material flow is concentrated in flux lines.