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Abstract
The paper presents a comparative analysis of the polymorphism of chiral phases (TGBA, TGBC, SC*) conducted on 28 selected members of the (R) or (S) 1-methylalkyl 4 '-(4“alkoxybenzoyloxy)tolan-4-carboxylate series ortho or/ and meta fluoro substituted. The roles of classical variables, (i) the length of the non chiral alkoxy chain (n = 7 to 18, typically), (ii) the length of the chiral end (m* = 8, 9, 10) and (iii) fluorine substitution are discussed with respect to the observations reported previously on related systems. We describe also a phase diagram combining an enantiomer and its racemate in order to analyze the effect of chirality. In the discussion we focus our interest on the direct clearing transition from the TGB state to the isotropic phase and on the still unexplained specific heat anomaly observed in the isotropic state which appears connected to this transformation.
