title: Direct observation of diffuse cone behavior in de Vries smectic-A and -C phases of organosiloxane mesogens.
abstract: Simultaneous and direct x-ray measurements of the smectic layer spacing, molecular tilt, and orientational order in the de Vries smectic A (SmA) and C (SmC) phases of two organosiloxane mesogens reveal that (i) the SmC (tilt) order parameter exponent β=0.26±0.01 for 2nd order SmA-SmC transition--in excellent agreement with the tricritical behavior, (ii) the siloxane and hydrocarbon parts of the molecules are segregated and oriented parallel to the director with very different degree of orientational order, and (iii) thermal evolution of the effective molecular length is different in the two phases.
authors.affiliation: Department of Physics, Kent State University, Kent, Ohio 44242, USA.
authors.forename: Hyungguen
authors.initials: H
authors.lastname: Yoon
authors.forename: Dena M
authors.initials: DM
authors.lastname: Agra-Kooijman
authors.forename: Khurshid
authors.initials: K
authors.lastname: Ayub
authors.forename: Robert P
authors.initials: RP
authors.lastname: Lemieux
authors.forename: Satyendra
authors.initials: S
authors.lastname: Kumar