Hostname: page-component-78c5997874-j824f Total loading time: 0 Render date: 2024-11-17T16:34:29.875Z Has data issue: false hasContentIssue false
  • English
  • Français

Application of Broad-Band Dielectric Spectroscopy for Investigations of Liquid Crystal - Porous Media Microcomposites

Published online by Cambridge University Press:  10 February 2011

G. P. Sinha ,
B. Batalla  and
F. M. Aliev
G. P. Sinha
Affiliation:
Department of Physics and Materials Research Center, PO BOX 23343, University of Puerto Rico, San Juan, PR 00931–3343, USA
B. Batalla
Affiliation:
Department of Physics and Materials Research Center, PO BOX 23343, University of Puerto Rico, San Juan, PR 00931–3343, USA
F. M. Aliev
Affiliation:
Department of Physics and Materials Research Center, PO BOX 23343, University of Puerto Rico, San Juan, PR 00931–3343, USA
Get access

Abstract

We applied ultra broad-band dielectric spectroscopy in the frequency range from 10–3 Hz to 109 Hz to investigate the effect of size, shape and volume fraction of the pores in the porous matrices on the dielectric properties of liquid crystals (LC) dispersed in these matrices. Measurements in such a broad frequency range make it possible to obtain detailed information on the important aspects of the electrical behavior of heterogeneous materials such as: conductivity, surface polarization, and influence of confinement on dynamics of molecular motion of polar molecules forming LC. We investigated alkylcyanobiphenyls in the isotropie, nematic and smectic phases dispersed in porous glasses (average pore sizes - 100 Å and 1000 Å) which have randomly oriented, interconnected pores, and anopore membranes (pore diameters - 200 Å and 2000 Å) with parallel cylindrical pores. Dispersion of LC resulted in qualitative changes of their dielectric properties. Analysis of broad-band dielectric spectra shows that in organic (LC) - inorganic (porous matrix) heterogeneous composites conductivity plays an important role at F <1 Hz. We observe the appearance of new dielectric modes: a very slow process with characteristic frequency ≃ (1 – 10) Hz and a second process in frequency range about (103 - 106) Hz. The slow process arises due to the relaxation of interfacial polarization at pore wall - LC interface. The origin of this could be due to absorption of ions at the interface. Another possibility is the preferential orientation of the permanent dipoles at pore surface. The second new mode is due to the hindered rotation of the molecules near the interface. Additionally we observed two bulk like modes due to the rotation of the molecules around their short and long axii which are modified.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 500: Symposium EE – Electrically Based Microstructural Characterization II , 1997 , 151
Copyright
Copyright © Materials Research Society 1998

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Hilfer, R., Phys. Rev. B 44, p. 60 (1991).Google Scholar
2. Aliev, F.M., Breganov, M.N., Sov. Phys. JETP 68, p. 70 (1989).Google Scholar
3. Schuller, J., Mel'nichenko, Yu.B., Richert, R., and Fischer, E.W., Phys. Rev. Lett. 73, p. 2224 (1994).Google Scholar
4. Arndt, M. and Kremer, F. in: Dynamics in Small Confining Systems II, edited by Drake, J.M., Klafter, J., Kopelman, R., Troian, S.M., (Mater. Res. Soc. Proc. 363, Pittsburgh, PA 1995), pp. 259–263.Google Scholar
5. Mel'nichenko, Yu., Schuller, J., Richert, R., Ewen, B. and Loong, C-K., J. Chem. Phys. 103, p. 2016 (1995).Google Scholar
6. Schuller, J., Richert, R., Fischer, E.W., Phys. Rev. B 52, 15232 (1995).Google Scholar
7. Arndt, M., Stannarius, R., Gorbatschow, W., and Kremer, F., Phys. Rev. E 54, 5377 (1996).Google Scholar
8. Aliev, F.M. and Sinha, G.P. in: Electrically based Microstructural Characterization, edited by Gerhardt, R.A., Taylor, S.R., and Garboczi, E.J. (Mater. Res. Soc. Proc. 411, Pittsburgh, PA 1996), pp. 413–418.Google Scholar
9. Rozanski, S.R., Stanarius, R., Groothues, H., and Kremer, F., Liquid Crystals 20, p. 59 (1996).Google Scholar
10. Sinha, G.P. and Aliev, F.M., MCLC 304, p. 309 (1997).Google Scholar
11. Sinha, G.P. and Aliev, F.M. in: Dynamics in Small Confining Systems HI, edited by Drake, J.M., Klafter, J. and Kopelman, R. (Mater. Res. Soc. Proc. 464, Pittsburgh, PA 1997), pp. 195–200.Google Scholar
12. Cummins, P.G., Danmur, D.A., and Laidler, D.A., MCLC 30, p. 109 (1975).Google Scholar
13. Lippens, D., Parneix, J.P., and Chapoton, A., J. de Phys. 38, p. 1465 (1977).Google Scholar
14. Wacrenier, J.M., Druon, C., and Lippens, D., Molec. Phys. 43, p. 97 (1981).Google Scholar
15. Bose, T.K., Chahine, R., Merabet, M., and Thoen, J., J. de Phys. 45, p. 11329 (1984).Google Scholar
16. Bose, T. K., Campbell, B., Yagihara, S., and Thoen, J., Phys. Rew. A 36, p. 5767 (1987).Google Scholar
17. Havriliak, S. and Negami, S., Polymer 8, p. 101 (1967).Google Scholar
18. Scaife, B.K.P., Principles of Dielectrics, (Clarendon Press, Oxford, 1989).Google Scholar