Abstract
We report an experimental study of structural transformations of disclination lines in nematic liquid crystals in microfluidic channels. The anchoring conditions of the channel walls enforce the generation of a disclination line of the wedge type in the absence of flow. The wedge disclination is transformed to a twist disclination by the flow of the nematic liquid crystal in the channel. The application of an electric field perpendicular to the channel axis induces a second transformation to a zigzag shape. The threshold field strength for the second transformation increases with increasing flow velocity. The experimental results are compared to predictions based on model director fields of the different disclination structures.
Highlights
Topological defects play an important role in soft condensed matter physics.[1]
Whereas line defects in solids are in most cases dislocations, line defects in Nematic liquid crystals (NLCs) are disclinations, which are characterized by a rotational displacement of the structure.[7,8,9]
When we switch on the flow, our experiment shows that the disclination line appears in the central region of the channel and the optical properties suggest the configuration of a twist disclination
Summary
Topological defects play an important role in soft condensed matter physics.[1]. Nematic liquid crystals (NLCs), small rod-shaped organic molecules exhibiting a liquid phase with long range orientational order, show a wealth of different topological defect structures, thereby providing a well suited experimental model system for studies which are significant to various areas beyond the field of NLCs. We have recently shown that the interplay between anchoring, flow and an applied electric field enables an enhanced control of disclinations in the channel, resulting, e.g., in a possibility to interrupt and reconnect a disclination line.[29] During the experiments described in ref. We conducted a detailed study of the structural transformations of disclination lines in microfluidic channels under the influence of flow and electric field and report here our results. 2 Materials and methods examples of wedge disclinations, i.e., the axis around which - n rotates is parallel to the disclination line and - n is confined to planes perpendicular to the line. Another type of disclination are twist disclinations.
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