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4-Nitrobenzyl-2,5-bis(4-n-alkyloxybenzoyloxy)benzoates exhibit SA phases which are characterized by an antiparallel packing of the molecules and a partial intercalation of the terminal alkyl chains. In binary systems of selected rod-like components the S, mixed phase can be stabilized or destabilized depending on the molecular length of the rod-like molecules. This unusual behaviour is mainly due to steric interaction and can be interpreted by a simple packing model. 2,5-Bis(4-n-alkyloxy-benzyloxy)benzoesaure-4-nitrobenzy~ester zeigen S,-Phasen, welche durch eineantiparallele Packung der Molekiile und eine teilweise Verzahnung der terminalen Alkylketten charakterisiert sind. In binaren Systemen von ausgewahlten stiibchenformigen Mischungskomponenten kann die S,-Mischphase entweder stabilisiert oder destabilisiert werden in Abhangigkeit von der Liinge der stabchenformigen Molekule. Dieses ungewohnliche Verhalten ist hauptsiichlich auf sterische Wechselwirkungen zuruckzufuhren und kann mit Hilfe eines einfachen Packungsmodells interpretiert werden.

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The destruction of the intercalated smectic A structure of a laterally bulky branched 1,4-phenylen dibenzoate A by addition of a rodlike cinnamate B was studied by the phase diagram as well as by calorimetric. x-ray and dielectric measurements. The thermal stability of the S, phase of compound A and its phase transition enthalpy decrease with increasing concentration of B. Furthermore, the destruction of the short range order of A is characterized by increasing layer distances, decreasing dipolar correlation and an increasing dielectric relaxation frequency only of component A.