title: Spontaneous periodic deformations in nonchiral planar-aligned bimesogens with a nematic-nematic transition and a negative elastic constant.
abstract: 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.
authors.affiliation: Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland.
authors.forename: V P
authors.initials: VP
authors.lastname: Panov
authors.forename: M
authors.initials: M
authors.lastname: Nagaraj
authors.forename: J K
authors.initials: JK
authors.lastname: Vij
authors.forename: Yu P
authors.initials: YP
authors.lastname: Panarin
authors.forename: A
authors.initials: A
authors.lastname: Kohlmeier
authors.forename: M G
authors.initials: MG
authors.lastname: Tamba
authors.forename: R A
authors.initials: RA
authors.lastname: Lewis
authors.forename: G H
authors.initials: GH
authors.lastname: Mehl