Imperfect Focal Conic Domains in Asmectics: a Textural Analysis.
Résumé
F o r P e e r R e Wehaveanalyzedoptical microscopyobservations of Focal ConicDomains (FCDs) withim- perfect ellipses onthebasis of thetheoretical concepts developedin[M. Klemanet al., Philos. Mag. 86, 4439(2006)]. Twotypes of imperfect ellipses are observed: withkinks (elementary imperfectionsresultingfromatopological interactionof adisclinationwithadislocation, attheir pointofjunction)beingeitherintheellipseplane('Mouse')orperpendiculartoit('Turtles'). The experimental conditions for theobservationof imperfect FCDs of bothtypes aredescribed. A model describingtheshapeofaMouse-typeellipseiscomparedtoobservations. Twoexperimental observationsinnematogenicsmectics(i.e., whichhaveasmectic →nematictransition)emphasize thepredominant roleof kinks indynamical phenomenainvolvingdislocations andFCDs: a)- a reversibleandsuddentemperatureinducedtransformationbetweentwoFCDtextures: FCDswith fewer kink-carryingdistortions (calledisometrictextures) andthehigher temperatureoneswith proliferationof kinks (callednon-isometric), b)- ashrinkingof theellipses uponheating, upto theirsuddenandtotal vanishingatatemperaturewell belowthephasetransition. Incontrast, in anon-nematogenicsmectic, theellipsesizedoesnotvaryuponheatinguntil theappearanceofthe isotropicphase.