Abstract
We determine elastic constants K11, K22, and K33 in two diphenylacetylene-core-based liquid crystals with azo and ester linkages. As we have already reported (Adv. Mater. (2014) 26, 1918), K33 is extremely large (sub-nN) compared with K11 (pN) in the azo compound, since cybotactic smectic (Sm) clusters exist in whole the nematic (N) phase range. As a natural consequence, K22 is expected to be also large. We confirm that K22 is several tens pN, which is smaller than K33 but larger than K11 by one order of magnitude, K33>>K22>>K11. This is the first compound, which has a larger K22 than K11. In the ester compound, which has no clusters in the N phase, all the elastic constants are in a pN range, and are in the usual order, K33>K11>K22. It is also important to note that not only K33 and K22 but also K11 show a pretransitional increase when the N-SmC phase transition temperature is approached.
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