L. V. Choudary

Phase transition studies in p-n-nonyloxybenzoic acid

Abstract Phase transitions of the liquid crystal p-n-nonyloxybenzoic acid have been investigated with density and ultrasonic velocity measurements. The variation of density with temperature confirms that the isotropic-nematic and nematic-smectic C transitions are of first order. All the phase transitions are confirmed by the variation of ultrasonic velocity with temperature. The adiabatic compressibility (βad), and Rao number (Rn) are also estimated.

Magnetic susceptibility investigations on EBBA

Abstract The temperature variation of the magnetic susceptibility (χg) of the liquid crystal N-(p-n-ethoxybenzylidene)p-n-butylaniline (EBBA) in the isotropic liquid and nematic phases is reported. Abrupt changes in Xg and S. ΔXg (S: order parameter, ΔXg : diamagnetic susceptibility anisotropy of the perfectly aligned phase) are observed at the isotropic-nematic phase transition. The order parameter is calculated using the estimated value of the molar susceptibility anisotropy.

Magnetic susceptibility studies of the liquid crystal N-(p-n-pentyloxybenzylidene) p-n-butylaniline

Abstract The temperature variation of the magnetic susceptibility (χ) of N-(p-n-pentyloxybenzylidene) p-n-butylaniline is reported in the isotropic, nematic, smectic A, smectic AG and smectic G phases. Abrupt changes in χand Δχ are observed at various phase transitions. An unusual decrease in χ with decreasing temperature is observed during the smectic A-smectic AG and smectic AG-smectic G transitions.

Magnetic Susceptibility and Order Parameter of EBCA

The variation of magnetic susceptibility (χ,) as a function of temperature of the liquid crystal EBCA is reported in isotropic liquid, nematic and solid phases χ, and S Αχ, undergo sudden changes at the phase transitions. The isotropic liquid-nematic transition is assigned to be of first order phase transition. The order parameter is calculated using an estimated value for the molar susceptibility anisotropy. Introduction Ncmatic liquid crystals [1, 2] are characterised by the orientational order parameter. The order parameter can be determined by several techniques [3-5]. Diamagnetic susceptibility is one of the parameters that can be used to determine the order parameter in nematic liquid crystals. The diamagnetic susceptibility measurements are alse useful in determining the order of the phase transitions in liquid crystals. We report here the diamagnetic susceptibility studies of N-(p-n-Ethoxybenzylidene) p-n-butylaniline, ECBA, as a part of our systematic study of the phase transitions in liquid crystals [6-9]. Theory The relation between Q, the macroscopic tensor order parameter and χ the anisotropic part of the diamagnetic susceptibility tensor χ (per unit volume) can be expressed as Q = Gt (1) where the constant G can be determined by setting Qzz = 1 in a perfectly aligned state. Hence Q*ß = GXlß oc, β — χ, y, ζ (2) G is given by G = (3) X(?X33 X22 Xll) where Ν is the number of molecules per unit volume and x¡ 1, χ22 and χ33 are the principal volume susceptibilités of an isolated molecule. 1 L . V . CHOUDARY, J . V . RAO and P . VENKATACHARYULU, Department of Physics, Nagarjuna University, Nagarjunanagar-522 510, India. 2 P. R. KISHORE, S. V. H. Engineering College, Machilipatnam, Andhra Pradesh, India. 174 L. V. Choudary et al. : Magnetic Susceptibility and Order Parameter of E B C A If one defines the macroscopic diamagnetic susceptibility anisotropy of a completely ordered nematic phase as Δ * = ; % 3 3 ± ( Ζ 2 2 + * . . ) ] (4) then

Molecular alignment studies in the nematic phase of N-(p-n-butoxybenzylidene) p-n-butylaniline

Abstract The molecular alignment in the nematic phase of N-(p-n-butoxybenzylidene)p-n-butylaniline (BBBA) is investigated by measuring the dielectric constant at 1 MHz. The relative effectiveness of electric and magnetic fields is discussed. These molecular alignment studies confirm that there are two nematic phases in BBBA.

Electric and magnetic field effects in the nematic phase of N-(p-n-pentyloxybenzylidene) p-n-butylaniline

Abstract The molecular alignment in the nematic phase of N-(p-n-pentyloxybenzylidene) p-n-butylaniline (PBBA) in the presence of electric and magnetic fields is investigated by measuring the dielectric constant at 1 MHz. The relative effectiveness of electric and magnetic fields in the nematic phase of PBBA is discussed.

Phase transition studies of the liquid crystal p-(p-ethoxyphenyl azo) Phenyl undecylenate

Abstract Phase transitions in the liquid crystal p-(p-ethoxyphenyl azo) phenyl undecylenate have been studied using specific volume and ultrasonic velocity measurements. The variation of specific volume with temperature in the solid, nematic and isotropic phases has been studied. The specific volume jump at the solid-nematic transition is 6.3%. The nematic-isotropic transition is found to be first order. Ultrasonic velocity studies in the nematic and isotropic phases confirm the nematic-isotropic transition. The adiabatic compressibility β ad , and the molar sound velocity Rn (Rao number) have been determined using the specific volume and ultrasonic velocity.