title: Short-range smectic fluctuations and the flexoelectric model of modulated nematic liquid crystals.
abstract: We show that the flexoelectric model of chiral and achiral modulated nematics predicts the compression modulus that is by orders of magnitude lower than the measured values. The discrepancy is much larger in the chiral modulated nematic phase, in which the measured value of the compression modulus is of the same order of magnitude as in achiral modulated nematics, even though the heliconical pitch is by an order of magnitude larger. The relaxation of a one-constant approximation in the biaxial elastic model used for chiral modulated nematics does not solve the problem. Therefore, we propose a structural model of the modulated nematic phase, which is consistent with the current experimental evidence and can also explain large compression modulus: the structure consists of short-range smectic clusters with a fourfold symmetry and periodicity of two molecular distances. In chiral systems, chiral interactions lead to a helicoidal structure of such clusters.
authors.affiliation: Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia.|Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
authors.forename: Nataša
authors.initials: N
authors.lastname: Vaupotič
authors.affiliation: Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia.
authors.forename: Samo
authors.initials: S
authors.lastname: Curk
authors.affiliation: Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond Street, G1 Glasgow, United Kingdom.
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Osipov
authors.affiliation: Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.|Faculty of Education, University of Ljubljana, Kardeljeva ploščad 16, 1000 Ljubljana, Slovenia.
authors.forename: Mojca
authors.initials: M
authors.lastname: Čepič
authors.affiliation: Toyota Physical and Chemical Research Institute, 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan.|Department of Chemistry, University of Warsaw, Zwirki i Wigury 101, 02-089 Warsaw, Poland.
authors.forename: Hideo
authors.initials: H
authors.lastname: Takezoe
authors.affiliation: Department of Chemistry, University of Warsaw, Zwirki i Wigury 101, 02-089 Warsaw, Poland.
authors.forename: Ewa
authors.initials: E
authors.lastname: Gorecka