Smectic ordering of homogeneous semiflexible polymers

A self-consistent-field theory for fluids of homogeneous wormlike polymers exhibiting a one-dimensional spatial variation is presented. We have extended the treatment of excluded-volume effects by adding an effective interaction term which describes the excluded volume between wormlike cylindrical segments and terminal (or end) segments of the polymer molecules. This enables us to find a smectic-A phase in the case of homogeneous semiflexible polymers. Using this framework, we have investigated the occurrence of smectic-A, nematic, and isotropic phases in the second-virial (Onsager) approximation. Phase diagrams are calculated for systems characterized by different rigidities (i.e., persistence lengths). For the case of infinitely rigid molecules, the nematic-smectic transition appears to be mostly second order. Systems of semiflexible molecules exhibit mainly a first-order smectic-nematic transition, and their isotropic-nematic-smectic triple points are accessed for different rigidity values. The nematic-smectic transition line is in good agreement with previous analytical calculations, which were also performed assuming the second-virial approximation. However, the values of the volume fraction at the nematic-smectic transition are large compared with computer simulation results, indicating limitations of the second-virial approximation.