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Generation of umbilics by Poiseuille flows
1Laboratoire de Physique des Solides, Université Paris-Sud, Bât. 510, 91405, Orsay Cedex, France, pieranski@lps.u-psud.fr.
The European Physical Journal. E, Soft Matter
|April 24, 2014
Summary
Point defects called umbilics in homeotropic nematic layers are unexpectedly generated by Poiseuille flows during sample cleaning. These umbilics form in π-walls where they are orthogonal to the flow, revealing new insights into defect formation.
Area of Science:
- Physics
- Materials Science
- Soft Matter Physics
Background:
- The Fredericks transition in nematic liquid crystals is described by a 2D vectorial order parameter.
- Umbilics, point defects in this field, were previously generated using magnetic fields.
Purpose of the Study:
- To investigate the serendipitous discovery of umbilic generation during sample cleaning.
- To identify the conditions necessary for controlled reproduction of umbilic generation.
- To understand the role of Poiseuille flows in umbilic formation.
Main Methods:
- Experimental observation of umbilic generation during sample cleaning.
- Systematic investigation of conditions leading to umbilic formation.
- Theoretical analysis of Poiseuille flow effects on the nematic order parameter field.
Main Results:
- Umbilics were serendipitously generated during sample cleaning.
- Umbilics are generated by Poiseuille flows.
- Umbilics appear in π-walls at points orthogonal to the flow direction.
- A relationship between Poiseuille flow and π-walls was established.
Conclusions:
- Poiseuille flows are identified as the cause of umbilic generation in this context.
- The specific location of umbilics within π-walls is explained by their orientation relative to the flow.
- This study reveals a novel mechanism for generating topological defects in liquid crystals.
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