Static Dielectric Studies of Two Nematogenic Compounds

Static dielectric constants of two nematogenic compounds viz., (i) 1-hexyl-4-(4-isothiocyanatophenyl) bicyclo [2 2 2] octane and (ii) 4′-(pentyloxy)-4-biphenyl carbonitrile, have been measured at different temperatures using a sensitive LCR bridge. Using these data the dipole moment associated with the molecules is estimated. The validity of this approach is discussed by comparing the order parameter S obtained from the refractive index data with the values of S computed from the predications of the mean-field theories. Boardewijk's theory is applied here with appropriate molecular parameters, to compute dipole-dipole correlation factors.

Keywords:

• dielectric constants
• dipole moment

Acknowledgments

We are grateful to Late Prof. S. Chandrashekar, Center for Liquid Crystal Research, Bangalore, for permitting us to use their facilities. Also, our thanks are due to Dr. Krishna Prasad and Dr. D. S. Shankar Rao for their help in collecting dielectric data. One of us (D. Gopalakrishna) is thankful to U.G.C. for a research fellowship. We are also grateful to CSIR New Delhi for a research project vide No. 03(0821)/EMR-II/97.

Notes

µ, = (µ_l + 2µ_t)/3.

• Average µ = 1.77 × 10⁻¹⁷ esu or (D) for 5OCB.

• Average µ = 1.30 × 10⁻¹⁷ esu or (D) for HIPBO.