Dynamics of dislocations is an important feature of condensed media that determines their behavior under stress. Recent studies have established quantitative correlations between the defect dynamics and macroscopic deformations for smectic liquid crystals (LCs)¹ and surface anchoring in cholesteric LCs.²

In the present work, we study the climb of edge dislocations in cholesteric LC samples driven by an electric field, using a direct three-dimensional visualization by means of regular and fluorescence confocal polarizing microscopy. The edge dislocations form in the bulk of a planar wedge cell with strong surface anchoring and small dihedron angle. The electric field, applied along the helix axis of the cholesteric LC with positive dielectric anisotropy, causes the layers undulations in neighboring Grandjean zones separated by the edge dislocation. When the applied electric field exceeds some critical value, the edge dislocation of half-pitch Burgers vector starts to climb along the planes of undulating layers in the direction of the increasing cell thickness. Its velocity is determined by a competition between the viscous drag and the free energy gained by the dislocation displacement. The undulating structure causes a jerky motion of the edge dislocation at low applied fields. The climb velocity increases when the field increases. In conclusion, we directly observed the climb of edge dislocations in cholesteric lamellae caused by the electric field and measured the climb velocity.

The work was supported by NSF Grants DMR-0504516 and DMS-0456221.

[1] C.Blanc, N.Zuodar, I.Lelidis, M.Kleman, J.-L.Martin, Phys. Rev. E 69, 011705 (2004).

[2] I.I.Smalyukh, O.D.Lavrentovich, Phys. Rev. Lett. 90, 085503 (2003).