Use of Atomic Force Microscopy in the Determination of Image Contrast in Microtomed Samples of Thermotropic Liquid Crystals

  • Timothy J. Bunning
  • Deborah L. Vezie
  • Peter D. Haaland
  • Hao Jiang
  • Pamela F. Lloyd
  • Edwin L. Thomas
  • W. Wade Adams

Abstract

Atomic force microscopy (AFM) is used in conjunction with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to explain for the first time the origin of image contrast in TEM for cholesteric liquid crystals (LC). Samples investigated were side-chain thermotropic siloxane-based cholesteric liquid crystalline materials whose room temperature glassy phase slowed for easy quenching of the LC order. Microtomed samples were prepared by cutting parallel to the helical axis and therefore perpendicular to a thin film cross-section. These sections exhibited a series of alternating dark and light bands whose sizes are related to the periodic structure of the cholesteric helix. The surfaces of the microtomed sections show a corrugated topology whose repeat distance corresponds to one half the pitch. Peak-to-valley heights on the order of 200 A were observed. Image contrast in the TEM was observed to increase substantially with time and electron dose due to beam damage of the materials. Since ∆I/1 is directly related to ∆t/t, the increase in contrast can be due to general mass loss (decrease in t) or preferential mass loss (increase in ∆t). AFM was performed on both unirradiated samples and samples that were exposed to large electron doses to explain the contrast mechanism.

Keywords

Atomic Force Microscopy Cholesteric Liquid Crystal Cellulose Acetate Butyrate Helical Axis Microtomed Section 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    H.L. DeVries, Rotatory power and other optical properties of certain liquid crystals, Acta. Cryst. 4: 219–226 (1951).CrossRefGoogle Scholar
  2. 2.
    P.J. Collings, “Liquid Crystals,” Princeton University Press, Princeton, N.J. 222 (1990).Google Scholar
  3. J. Voss and B. Voss, SEM Studies of cholesteric liquid crystals, Z. Natureforsch .31A:1661–1663Google Scholar
  4. 4.
    T.J. Bunning, H.E. Klei, E.T. Samulski, R.L.Crane, and R.J. Linville, Bilayer structures in cholesteric, cyclic siloxane liquid crystals, Liq. Cryst. 10: 445–456 (1991).CrossRefGoogle Scholar
  5. (1976).
    M.J. Costello, S. Meiboom, and M. Sammon, Electron microscopy of a cholesteric liquid crystal and its blue phase. Phys. Rev. A. 29: 2957–2959 (1984).Google Scholar
  6. 5.
    M.J. Costello, S. Meiboom, and M. Sammon, Electron microscopy of a cholesteric liquid crystal and its blue phase. Phys. Rev. A. 29: 2957–2959 (1984).Google Scholar
  7. 6.
    D.W. Berreman, S. Meiboom, J.A. Zasadzinski, and M.J. Sammon, Theory and simulation of freeze-fracture in cholesteric liquid crystals, Phys. Rev. Lett. 57: 1737–1740 (1986).CrossRefGoogle Scholar
  8. 7.
    P. Sixou, J.M. Gilli, A. Ten Bosch, F. Fried, P. Maissa, L. Varichon, and M.H. Godinho, Cholesteric mesophases, Physica Scripta, T35: 47–52 (1991).CrossRefGoogle Scholar
  9. 8.
    J.M. Gilli, M. Kamaye, and P. Sixou, Phases bleues “figees” dans un polysiloxane mésomorphe, J. Phys. France, 50: 2911–2918 (1989).CrossRefGoogle Scholar
  10. 9.
    V. Dave, W.G. Glasser, and G. Wilkes, Evidence for cholesteric morphology in films of cellulose acetate butyrate by transmission electron microscopy, Polym. Bull. 29: 565–570 (1992).CrossRefGoogle Scholar
  11. 10.
    J. Giasson, J-F Revol, A.M. Ritcey, and D.G. Gray, Electronic microscopic evidence for cholesteric structure in films of cellulose and cellulose acetate, Biopolym, 27: 1999–2004 (1988).CrossRefGoogle Scholar
  12. 11.
    H. Hara, T. Satoh, T. Toya, S. Iida, S. Orii, and J. Watanabe, Cholesteric liquid crystalline polyesters. 1.) Cholesteric Liquid Crystalline Copolyesters Based on Poly(chloro-1,4-phcnylene trans-1,4-cyclohexanedicarboxylate), Macromolecules, 2 1: 1419 (1988).Google Scholar
  13. 12.
    T.J. Bunning, D.L. Vezie, P.F. Lloyd, P.D. Haaland, E.L. Thomas, and W.W. Adams, Cholesteric liquid crystals: image contrast in the TEM, Liquid Crystals,in press.Google Scholar
  14. 13.
    A. Saupe, Disclinations and properties of the director field in nematic and cholesteric liquid crystals, Mol. Cryst. Liq. Cryst. 21: 211–238 (1973).CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1994

Authors and Affiliations

  • Timothy J. Bunning
    • 1
  • Deborah L. Vezie
    • 2
  • Peter D. Haaland
    • 3
  • Hao Jiang
    • 3
  • Pamela F. Lloyd
    • 4
  • Edwin L. Thomas
    • 2
  • W. Wade Adams
    • 1
  1. 1.Wright Laboratory/MLPJWright-Patterson AFBUSA
  2. 2.Dept. of Materials Science and EngineeringMassachusetts Institute of TechnologyCambridgeUSA
  3. 3.Lawrence Associates, Inc.DaytonUSA
  4. 4.UES, Inc.DaytonUSA

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