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New hockey stick-shaped mesogens with a lateral methyl group inserted between the m-alkyloxy-chain and the azomethine connecting group, 4-(3-n-alkyloxy-2-methyl-phenyliminomethyl) phenyl-4-n-alkyloxycinnamates have been synthesised. The interesting feature of these hockey stick-shaped mesogens is the appearance of the nematic phase in addition to two polymorphic tilted smectic phases - the synclinic smectic C (SmCs) and the anticlinic SmCa phase. Physical characterisation of these mesogens has been carried out using polarising optical microscopy, differential scanning calorimetry, optical birefringence, X-ray diffraction (XRD), electro-optical and dielectric spectroscopy measurements. The SmCs-SmCa phase transition is accompanied by only a small calorimetric signal but causes a pronounced change in the optical textures. Orientational order parameters determined from the birefringence measurements have been compared with those estimated from XRD patterns. Dielectric measurements point to the formation of small 'soft' ferroelectric clusters responsible for a low frequency absorption range. [ABSTRACT FROM AUTHOR]

Twelve new five-ring bent-core compounds have been synthesised which are derived from 2-nitroresorcinol and which contain only ester linkage groups. Their mesophase behaviour was investigated by polarising microscopy, X-ray diffraction and electro-optical measurements. It was found that most of the compounds studied form a B7 phase. For several compounds, a phase transition between a B7 high-temperature phase (B7H) and a B7 low-temperature phase (B7L) was clearly detected by calorimetry, by a small change of the texture and by X-ray diffraction measurements. For one compound, (A12), well-aligned samples were obtained which allowed a more detailed structural characterisation of the B7 phases. Interestingly, by fast cooling of the isotropic liquid, the same compound forms a metastable columnar phase. Furthermore, the binary system composed of the compound A12 and a member of the B7 parent series was investigated. X-ray diffraction measurements give evidence that the B7 phases of both mixing components are completely miscible, i.e. they belong to the same phase type. [ABSTRACT FROM AUTHOR]

Two strongly polar 4-(4-cyanobenzyloxy)benzylidene 4- n -alkylanilines were synthesized for the first time and mixed with the hydrophilic aerosil A 300. The compounds, showing a rich polymorphism, and the mixtures were investigated by calorimetric and dielectric methods. Phase transitions of first and second order were detected. Neither the phase transition temperatures nor dielectric relaxation times are strongly influenced by addition of aerosil up to 20%. [ABSTRACT FROM AUTHOR]