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Hydrocarbon linked mesogenic dimers are found to exhibit an additional nematic phase below the conventional uniaxial nematic phase as conﬁrmed by x-ray diffraction. The phase produces unusual periodic stripe domains in planar cells. The stripes are found to be parallel to the rubbing direction (in rubbed cells) with a well-deﬁned period equal to double the cell gap. The stripes appear without external electromagnetic ﬁeld, temperature or thickness gradients, rubbing or hybrid alignment treatments. Simple modeling proposes a negative sign for at least one of the two elastic constants: splay and twist, as a necessary condition for the observed pattern.
Kohlmeier, A. et al. (2010). Spontaneous periodic deformations in nonchiral planar-aligned bimesogens with a nematic-nematic transition and a negative elastic constant. Physical Review Letters , vol. 105, pp. 1-4. DOI:10.1103/PhysRevLett.105.167801