Posnjak Topological Formations in Chiral Nematic Droplets

1. Auflage 2018
ISBN: 978-3-319-98261-8
Verlag: Springer International Publishing
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 192 Seiten, eBook

Reihe: Springer Theses

In this book Gregor Posnjak unravels the long-standing mystery of the internal director structure of chiral nematic droplets, which has been studied both experimentally and theoretically since the 1970s. To do so, he develops a new method for the reconstruction of director fields from a set of fluorescent confocal polarising microscopy images, which he augments with a simulated annealing algorithm. This allows the full reconstruction of 3D director fields, describing the ordering of the liquid crystal. The reconstruction procedure and its principles, which are applicable to other methods of studying vector fields, are explained in detail. The method is subsequently used to explore complex 3D structures in chiral nematic liquid crystal droplets with perpendicular surface anchoring. Twentyfour distinct states are identified and presented, including the layered structures of different symmetries and states with multiple topological point defects, separated by localized chiral structures. In closing, the book reports on the first observation of topological point defects with higher topological charges q = -2 and q = -3. 

Zielgruppe

Research

Autoren/Hrsg.

Posnjak, Gregor

Inhaltsverzeichnis

1;Supervisor’s Foreword;6
2;Acknowledgments;8
3;Abstract;9
4;Contents;10
5;1 Introduction;13
5.1;References;15
6;2 Liquid Crystals—An Overview;16
6.1;2.1 Nematic Order;16
6.2;2.2 Chiral Nematics;17
6.3;2.3 Free Energy Expansion;19
6.4;2.4 Anchoring;21
6.5;2.5 Topological Defects in Nematics;22
6.5.1;2.5.1 Topological Defects in Two Dimensions;24
6.5.2;2.5.2 Three-Dimensional Topological Defects;25
6.5.3;2.5.3 Topological Defects in Chiral Nematics;30
6.6;2.6 Optics of Liquid Crystals;32
6.6.1;2.6.1 Optics of Chiral Nematic Liquid Crystals;34
6.7;References;36
7;3 Liquid Crystal Droplets;39
7.1;3.1 Chiral Nematic Droplets;41
7.2;3.2 Chiral Nematic Droplets with Homeotropic Anchoring;43
7.3;References;46
8;4 Experimental Inspection of Director Fields;50
8.1;4.1 Confocal Microscopy;52
8.2;4.2 Fluorescent Confocal Polarising Microscopy;54
8.3;References;60
9;5 Materials and Experimental Setup;61
9.1;5.1 Materials;61
9.1.1;5.1.1 Liquid Crystal Mixture;61
9.1.2;5.1.2 Emulsion Matrix;63
9.1.3;5.1.3 Fluorescent Dye;64
9.1.4;5.1.4 Sample Preparation;65
9.2;5.2 Microscopy Setup;66
9.2.1;5.2.1 Numerical Processing of Data and Visualisation;68
9.3;References;69
10;6 Simulated Annealing for Determination of z-Component Sign;71
10.1;6.1 Testing the Algorithm;72
10.1.1;6.1.1 Continuity as the Evaluating Criterion in the Boltzmann Factor;74
10.1.2;6.1.2 Boltzmann Factor with Landau-de Gennes Free Energy;76
10.2;6.2 Implementing the Simulated Annealing Algorithm on Experimental Data;78
10.2.1;6.2.1 Bleaching Corrections;80
10.2.2;6.2.2 Deconvolution;80
10.2.3;6.2.3 Offset Correction and Normalisation;83
10.3;6.3 Calibration of the Annealing Algorithm on Experimental Data;85
10.3.1;6.3.1 Nematic Homeotropic Droplet;85
10.3.2;6.3.2 Chiral Nematic Droplet with a Complex Director Structure;88
10.3.3;6.3.3 Skyrmions and Torons in Homeotropic Cells;91
10.4;References;94
11;7 Structures in Chiral Nematic Droplets with Homeotropic Anchoring;96
11.1;7.1 Droplet with a Single Point Defect and a Cholesteric Bubble;96
11.2;7.2 Droplets with Layered Structures;99
11.2.1;7.2.1 Droplets with Bent Layers;100
11.2.2;7.2.2 Droplets with Flat Layers;102
11.2.3;7.2.3 Cylindrical Layers;103
11.2.4;7.2.4 Cholesteric Finger with a Central Hyperbolic Point Defect;106
11.2.5;7.2.5 The Lyre/Yeti Structure;107
11.2.6;7.2.6 Droplets with Disclination Lines;110
11.2.7;7.2.7 Combinations of Cholesteric Bubbles and Cholesteric Cylinders;119
11.3;7.3 Strings of Point Defects;124
11.4;7.4 Higher-Charge Topological Point Defects;141
11.4.1;7.4.1 -2 Point Defect;141
11.4.2;7.4.2 -3 Point Defect;145
11.4.3;7.4.3 Structure of the Higher-Charge Point Defects;149
11.5;7.5 Topological Molecules;152
11.5.1;7.5.1 Topological Molecules with Higher-Charge Defects;152
11.5.2;7.5.2 Topological Molecules with Disclination Lines;160
11.5.3;7.5.3 Other Topological Molecules;165
11.6;References;166
12;8 Schematic Construction of Droplets with Multiple Cholesteric Bubbles;168
12.1;8.1 Construction of String-Like Constellations;168
12.2;8.2 Construction of Topological Molecules with Higher-Charge Point Defects;170
12.3;Reference;175
13;9 Discussion;176
13.1;References;187
14;10 Conclusion;189
14.1;References;192