A Study on Phase Transition Behavior of Low Molecular Weight Liquid Crystal and Its Blend with a Polymer Using Alternating Current Impedance Spectroscopy

Ahn W; Lee SH; Rho SB; Park LS; Kim CY

Korea Polymer Journal, Vol.6, No.4, 295-301, October, 1998

Ahn W, Lee SH, Rho SB, Park LS, Kim CY

Alternating Current Impedance Spectroscopy (ACIS) was used to characterize phase transition behabior of a low molecular weight liquid crystal, 4''-n-heptylbiphenyl (7CB) and its blend with an amorphous polymer, poly(methyl methacrylate) (PMMA). ACIS showed that pure 7CB has a single relaxation time due to a large permanent dipole moment associated with cyane (-CN) group in the 7CB molecule, which could be deduced from the Nyquist plot ot the impedance spectra of 7CB. The Nyquist plot of 7CB showed a remarkable change in scale near T_NI and T_CN, but almost perfect semicircles in complex plane. Changes of the electrical properties of PMMA/7CB blend were also utilized to investigate the relationship between the electrical properties and the phase behavior. The maximum resonance frequency, f_max at which -Z" of the blend becomes maximum, was considered to be a very sensitive probe to investigate the physico-chemical changes within the samples.

[References]

Impedance Spectroscopy, ed. by J.R. Mcdonald, John Wiley & Sons, Inc (1987)
Bruce PG, Polymer Electrolyte Review, eds. by J.R. MacCallum and C.A. Vincent, Ch. 8, Elsevier, N.Y. (1987)
Wang Y, Snyder DD, Nelson GJ, Mol. Cryst. Liq. Cryst., 149, 163 (1987)
Kelly J, Seekola D, Proc. SPIE, 1257, 17 (1990)
Myamoto A, Kikuchi H, Kobayashi S, Morimura Y, Kajiyama T, Macromolecules, 24, 3915 (1991)
Chelkowski A, Dielectric Physics, Ch. IV, Elsevier, N.Y. (1980)
de Gennes PG, The Physics of Liquid Crystals, Clarendon Press, Oxford (1974)
Ahn W, Kim H, Kim SC, Kim CY, Macromolecules, 25, 5002 (1992)
Wang Y, Liu SW, Huo R, SAE Paper. No. 860352 (1986)

[1] Impedance Spectroscopy, ed. by J.R. Mcdonald, John Wiley & Sons, Inc (1987)

[2] Bruce PG, Polymer Electrolyte Review, eds. by J.R. MacCallum and C.A. Vincent, Ch. 8, Elsevier, N.Y. (1987)

[3] Wang Y, Snyder DD, Nelson GJ, Mol. Cryst. Liq. Cryst., 149, 163 (1987)

[4] Kelly J, Seekola D, Proc. SPIE, 1257, 17 (1990)

[5] Myamoto A, Kikuchi H, Kobayashi S, Morimura Y, Kajiyama T, Macromolecules, 24, 3915 (1991)

[6] Chelkowski A, Dielectric Physics, Ch. IV, Elsevier, N.Y. (1980)

[7] de Gennes PG, The Physics of Liquid Crystals, Clarendon Press, Oxford (1974)

[8] Ahn W, Kim H, Kim SC, Kim CY, Macromolecules, 25, 5002 (1992)

[9] Wang Y, Liu SW, Huo R, SAE Paper. No. 860352 (1986)