title: Optical and confocal microscopy observations of screw dislocations in smectic-A liquid crystals.
abstract: We present experimental evidence of the presence of isolated screw dislocations in smectic-A liquid crystals observed by polarizing microscopy. In a wedge-shaped homeotropic cell, the edge and screw dislocations interaction gives rise to a strong-enough optical contrast and makes visible their mutual intersections at temperatures close to the smectic-A to smectic-C phase transition temperature. The nature of the defects is confirmed by confocal microscopy observations. At large scale we observe a forest of screw dislocations, perpendicular to the smectic layers, across the thickness of the cell (end-on configuration). Their density varies between 10(9) and 10(12) m-2. In situ observations of dislocations under stress, in the optical microscope, provide quantitative information about the screw-edge dislocation interactions. The latter interaction is calculated in the unharmonic approximation and it gives rise to an observed yield stress.
authors.affiliation: Groupe des Cristaux Liquides, Université de Picardie, 33 rue Saint-Leu, 80039 Amiens, France.
authors.forename: I
authors.initials: I
authors.lastname: Lelidis
authors.forename: C
authors.initials: C
authors.lastname: Blanc
authors.forename: M
authors.initials: M
authors.lastname: Kléman