COLUMNAR AND SMECTIC ORDER IN BINARY-MIXTURES OF ALIGNED HARD CYLINDERS

We examine possible nematic to smectic and nematic to columnar phase transitions for binary mixtures of perfectly parallel aligned hard cylinders with equal diameters but different lengths by using the free-energy functional within the third virial coefficient approximation. The regions of stability are located and the phase diagram of the system is calculated for different values of the ratio of the two cylindrical lengths. The nematic phase can directly transform into the columnar phase for values with a length ratio smaller than 0.635, showing that dispersity in molecular length can stabilize columnar versus smectic ordering of these mixtures. © 1994 The American Physical Society.