Tunable backflow in chiral nematic liquid crystals via twist-bend nematogens and surface-localised in-situ polymer protrusions

Vinay Joshi*, Daniel A. Paterson, John M.D. Storey, Corrie T. Imrie, Liang Chy Chien

*Corresponding author for this work

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Dynamic electro-optic response of the liquid crystal (LC) director shows a backflow effect that is manifested as an optical bounce in chiral nematic LCs (N*LC) during field-induced homeotropic-twisted transition. The bend elastic constant (K33) strongly influences the dynamics of backflow at the N*LC in homeotropic-twisted transition. The cyanobiphenyl LC dimers – CB7CB, CB9CB and CB11CB – possess a unique characteristic of inherent bend molecular configuration that lowers K33. With the modulation of the effective K33 in dimer-doped N*LCs, we report the tunability of the optical bounce that decreases with the increase in the length of flexible spacers in LC dimers. The doped LC dimers with short spacer lengths not only generate a strong backflow with an enhanced twist degeneracy of the LC director across the cell, but also prolong the time of disappearance of the optical bounce. Furthermore, we demonstrate the suppression of the optical bounce with surface localised polymer protrusions having 50–100 nm diameters, which allow faster dynamic relaxation process and reduced backflow. We envision a novel design of a tunable microfluidic device for precise flow control of organic or inorganic matter in LC medium that exploits the tunable backflow in LC dimer-doped N*LCs.

Original languageEnglish
Pages (from-to)2327-2336
Number of pages10
JournalLiquid Crystals
Volume44
Issue number14-15
Early online date12 Sep 2017
DOIs
Publication statusPublished - 2017

Fingerprint

Liquid Crystals
Nematic liquid crystals
Liquid crystals
Polymers
liquid crystals
Dimers
polymers
dimers
spacers
microfluidic devices
Relaxation processes
Elastic constants
Electrooptical effects
Flow control
Microfluidics
doped crystals
electro-optics
elastic properties
Modulation
retarding

Keywords

  • Backflow
  • liquid crystal dimers
  • optical bounce
  • polymer stabilisation
  • topological defects

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

Tunable backflow in chiral nematic liquid crystals via twist-bend nematogens and surface-localised in-situ polymer protrusions. / Joshi, Vinay; Paterson, Daniel A.; Storey, John M.D.; Imrie, Corrie T.; Chien, Liang Chy.

In: Liquid Crystals, Vol. 44, No. 14-15, 2017, p. 2327-2336.

Research output: Contribution to journalArticle

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abstract = "Dynamic electro-optic response of the liquid crystal (LC) director shows a backflow effect that is manifested as an optical bounce in chiral nematic LCs (N*LC) during field-induced homeotropic-twisted transition. The bend elastic constant (K33) strongly influences the dynamics of backflow at the N*LC in homeotropic-twisted transition. The cyanobiphenyl LC dimers – CB7CB, CB9CB and CB11CB – possess a unique characteristic of inherent bend molecular configuration that lowers K33. With the modulation of the effective K33 in dimer-doped N*LCs, we report the tunability of the optical bounce that decreases with the increase in the length of flexible spacers in LC dimers. The doped LC dimers with short spacer lengths not only generate a strong backflow with an enhanced twist degeneracy of the LC director across the cell, but also prolong the time of disappearance of the optical bounce. Furthermore, we demonstrate the suppression of the optical bounce with surface localised polymer protrusions having 50–100 nm diameters, which allow faster dynamic relaxation process and reduced backflow. We envision a novel design of a tunable microfluidic device for precise flow control of organic or inorganic matter in LC medium that exploits the tunable backflow in LC dimer-doped N*LCs.",
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note = "Acknowledgements This work was supported by the Ohio Third Frontier (OTR) Venture Startup Fund from Ohio Development Services Agency (ODSA) under Grant No. TECG 2015–0128. The SEM images were obtained at the characterisation facility of the Liquid Crystal Institute, Kent State University, supported by the Ohio Research Scholars Program Research Cluster on Surfaces in Advanced Materials. The authors gracefully acknowledge the technical support provided by Dr Min Gao and Dr Lu Zou for microscopy experiments. The authors thank Kai-Han Chang, Sahil Gandhi and Andrii Varanytsia for their technical support during electro-optical experiments. L.-C.C. initiated and supervised the research. D.A.P., J.M.D.S. and C.T.I synthesised the LC dimers CB7CB, CB9CB and CB11CB. L.-C.C. conceived the idea of OB modulation in bimesogen-mediated long-pitch cholesteric liquid crystals and polymer stabilisation for suppression of OB. V.J. produced the electro-optical cells and carried out electro-optic measurements, POM and SEM. V.J. wrote the manuscript.",
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N1 - Acknowledgements This work was supported by the Ohio Third Frontier (OTR) Venture Startup Fund from Ohio Development Services Agency (ODSA) under Grant No. TECG 2015–0128. The SEM images were obtained at the characterisation facility of the Liquid Crystal Institute, Kent State University, supported by the Ohio Research Scholars Program Research Cluster on Surfaces in Advanced Materials. The authors gracefully acknowledge the technical support provided by Dr Min Gao and Dr Lu Zou for microscopy experiments. The authors thank Kai-Han Chang, Sahil Gandhi and Andrii Varanytsia for their technical support during electro-optical experiments. L.-C.C. initiated and supervised the research. D.A.P., J.M.D.S. and C.T.I synthesised the LC dimers CB7CB, CB9CB and CB11CB. L.-C.C. conceived the idea of OB modulation in bimesogen-mediated long-pitch cholesteric liquid crystals and polymer stabilisation for suppression of OB. V.J. produced the electro-optical cells and carried out electro-optic measurements, POM and SEM. V.J. wrote the manuscript.

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