"The entropy change at nematic – isotropic transition for dimers with odd spacers is comparable to that of monomers while for even spacer dimers the transitional entropy is typically three times larger. The behaviour of the transitional entropy suggests that the orientational order for even spacer dimers should be significantly greater than that for odd spacer dimers" . The conclusion is cited from the article published in (http://scholarsresearchlibrary.com/archive.html). It directs conditions when birefringence for dimeric LC exists.
They show birefringence if they form a liquid crystaline phase. Attached you can find a birefringence study on dimers.
the light travel across the liquid crystal molecules in such way that its velocity depends on the orientation of molecules. This is the origin of birrefringency.
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