Transverse interlayer order in lyotropic smectic liquid crystals

We present a theoretical and numerical study of the coupling of orientational and positional order in a smectic-A phase of hard rods. Our density functional analysis suggests a strong spatial modulation of the orientation distribution function. Computer simulations confirm this prediction and show that the modulation is due to the presence of a finite concentration of particles positioned between smectic layers and oriented perpendicular to the director. This peculiar modulation of the orientational order should be experimentally observable in Iyotropic smectic liquid crystals.