The phase diagrams of four binary mixtures of chemically similar smectogenic mesogens differing only in molecular length are investigated. In these bidisperse systems the length ratio varies systematically. The phase diagrams show the stabilization of the smectic A and the destabilization of the smectic C phase with increasing length ratio as a general trend. Detailed small-angle X-ray diffraction and electro-optic measurements revealed a decrease in smectic translational order and a continuous reduction of the tilt angle with increasing length difference. These surprising results are of general interest for the understanding of the structure and dynamics of smectic phases. The remarkably strong impact of the length difference on the smectic layer structure and the phase behavior is discussed from a mechanistic point of view taking into account sterical interactions. For the observed structural changes in these bidisperse smectics we propose pronounced out-of-layer fluctuations with increasing length difference as driving force, causing neighboring molecules within nearest layer into a smectic A-like packing.
Even though the fluid tilted smectic C (SmC) phase is one of the most common phases in thermotropic liquid crystals, the lyotropic analogue to SmC is practically unknown so far. One of the rare examples, a lyotropic liquid crystalline diol, which was reported in 1991 to show this phase, was re-examined by means of detailed X-ray diffraction and polarised optical microscopy. Although the diol possesses a smectic C promoting phenylpyrimidine core, it was not possible to verify the existence of a SmCanalogue lyotropic phase. Instead, the phase diagram shows the existence of five different lyotropic phases identified as nematic, lamellar L a and hexagonal as well as two novel complex 2D-correlated lyophases. Results obtained by electron density calculations and X-ray diffraction data strongly suggest that the structure of one of these phases possesses a pseudo-c2mm symmetry and is built up of two different kinds of columns, whereas the other one is a ribbon phase of the oblique plane group p2.
A compact, efficient projection system using an LCOS display as a programmable diffractive element is presented. The device accepts DVI data representing 1280 × 1024 pixels at 24 bits per pixel. The holograms required for display on the LCOS device are calculated in real time using specially developed algorithms.
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