A. K. George

Specific heat ratio, Grüneisen parameter and Debye temperature of crude oil

There has been substantial interest in determining the thermo-physical properties of hydrocarbon fluids. We have used three different experimental techniques: ultrasonic interferometry to determine the velocity of compressional wave, differential scanning calorimetry to determine the specific heat and the Anton Paar density meter to determine the density of crude oil sample over a wide range of temperatures varying from 20 to 70 °C. These data are used in thermodynamic relations to evaluate the specific heat ratio, the Gruneisen parameter, the Debye temperature and the long wavelength limit of the structure factor. The packing fraction obtained for crude oil is found to be closer to the values of other dense liquid fluids.

Use of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures

We report on a laser induced photoacoustic study of the nematic-to-isotropic transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002, BL032 and BL035. A simple analysis of the experimental data using the Rosencwaig-Gersho theory shows that the heat capacities of all these compounds exhibit a sharp peak as the temperature of the sample is varied across the transition region. Also, substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases have been noticed for all the mixtures. The increased light scattering property of the nematic phase may be the reason for the enhanced photoacoustic signal amplitude in this phase.

Photoacoustic studies on thermal parameters of liquid crystal mixtures

Complete thermal characterization of liquid crystal mixtures in the smectic phase consisting of various relative volume fractions of cholesterol and 1-hexadecanol have been carried out using the photoacoustic technique. Thermal diffusivity values of these liquid crystal mixtures are evaluated using the open cell photoacoustic technique whereas the thermal effusivity value is measured using the conventional photoacoustic technique. From the measured values of these transient thermophysical parameters, the thermal conductivity and heat capacity of the sample under investigation are calculated. Analyses of the results show that all the thermophysical parameters depend strongly on the volume fraction of the constituents. Results are interpreted in terms of enhanced hydrogen bonding and the consequent enhancement in cohesive thermal energy transport with increasing volume fraction of 1-hexadecanol.

Thermal variation of surface tension at liquid crystal–isotropic liquid interface

The surface tension of two nematic liquid crystals bounded by an isotropic liquid (glycerin) was measured as a function of temperature. A spinning drop technique was used for the measurements. Unlike monotonically decreasing dependence found in most isotropic liquids, the surface tension−temperature characteristic showed more than one region with positive slope in the nematic phase. A sharp increase in surface tension was observed near the nematic‐isotropic transition temperature. The results obtained are in qualitative agreement with the theoretical predictions of Croxton and Chandrasekhar.

Open-cell photoacoustic investigation of the thermal effusivity of liquid crystals

We report the use of an open photoacoustic cell configuration for the evaluation of thermal effusivity of liquid crystals. Initially, the method is calibrated using water and glycerol as transparent liquid samples, and the role of thermal conductivity of these liquids on the photoacoustic signal amplitude is discussed. To demonstrate the appli- cation of the present method for the evaluation of thermal effusivity of liquid crystals, we have used certain multicomponent nematic liquid crys- tal mixtures, namely BL001, BL002, BL032, and BL035. Each of these liquid crystal mixtures contains four to nine components and are primarily based on the cyanobiphenyl structure. The measured values of thermal effusivity of BL001 and BL002 were found to be almost the same, but differ from those of BL032 and BL035, which implies a difference in composition of the latter two from the former two mixtures.

Pre-Transitional Surface Ordering and Disordering at Liquid Crystal-Isotropic Liquid Interface

Abstract The existence of pre-transitional surface ordering and disordering at the liquid crystal-isotropic liquid interface has been established from the surface tension measurements. A spinning-drop technique has been used for this study. Measurements were carried out in the smectic A(SA), nematic (N) and isotropic (I) phases of the liquid crystals and reproducible results were obtained. The results suggest that the equilibrium value of γ changes discontinuously in the N and SA phases. The slope dγ/dT is positive for both the isotropic phase just above T NI as well as for the nematic phase just below it. Similar positive slope has been obtained in the vicinity of T AN. A positive value of dγ/dt implies excess surface order than that of the bulk interior. From the density measurements it has been observed that there is a correlation between the anomalies in the temperature dependence of surface tension and density in the isotropic phase.

Novel fluorinated ferroelectric organosiloxane liquid crystals

A progress report on the synthesis and characterisation of a series of fluorinated chiral bi-mesogen low molar mass organosiloxane materials is presented. The mesogenic moiety is identical to that in the TSiKN65F mono-mesogen material reported by Naciri et al., which displays a de Vries-type SmA* phase. The parameter varied across the series is the length of the alkyl chain linking the mesogen moiety to the siloxane. The material with 10 carbon atoms in the chains displays a stable smectic phase with ferroelectric response at room temperature, whereas the materials with 6, 7 and 8 carbon atoms tend to crystallize.

Equation of state of crude oil through temperature dependent ultrasonic measurements

Ultrasound interferometery has been used to determine the velocity of propagation of compressional waves in two different samples of crude oil over a wide range of temperatures. The corresponding bulk density of the samples at similar conditions has also been measured using an Anton Paar density meter. These experimentally measured quantities form the basis for the thermo-physical characterization of crude oil through thermodynamic relations. This facilitated the evaluation of the acoustic impedance, compressibility and the coefficient of thermal expansion as a function of temperature. Simple analytical relations are suggested to describe the temperature dependence of thermo-physical functions. The equation of state for the crude oil has been set up by using these data. Our study yields a very close agreement to the reservoir conditions of the respective oil fields and to other empirical relations.

Optical anisotropy of nematic liquid crystals

Temperature dependence of the principal refractive indices (n 0 and ne ) of three nematic liquid crystals were measured using an Abbe refractometer with a large refractive index prism. The variatio...

Thermo-elastic and thermodynamic properties of light and heavy crude oil

Three different experiments, viz., ultrasound interferometry, differential scanning calorimetry, and density measurements were carried out over a wide range of temperature varying from 20°C to 70°C in light, heavy, and a mixture of light and heavy crude oil samples which differ considerably in its American Petroleum Institute gravity. The properties of the mixture have been discussed in terms of its deviation from the ideal values of mixing. The directly measured quantities such as the compression wave velocity, the specific heat at constant pressure, and the density were used to evaluate the temperature dependence of adiabatic compressibility, coefficient of volume expansion and the acoustic impedance. A correlation between thermo-elastic and thermodynamic functions of crude oils has been investigated. In particular, the ratio of the specific heats has been determined by making use of the thermo-elastic functions, which was further used to estimate the specific heat at constant volume. The values of the isothermal compressibility and the coefficient of volume expansion are used to evaluate the pressure–temperature dependence of crude oil conforming to in-situ reservoir conditions.