Gyan P. Johari

Dielectric Study of the Pressure Dependence of Intermolecular Association in Isomeric Octyl Alcohols

The equilibrium dielectric constant and density of 2‐octanol, 3‐octanol, 2‐methyl‐3‐heptanol, and 5‐methyl‐3‐heptanol have been measured as a function of pressure to 4 kbar from about 100°C to the freezing temperature. The isobaric temperature dependence and the isothermal pressure dependence of the dielectric constant are both sensitive functions of temperature, pressure, and the isomeric nature of the alcohol. Analysis of the data in terms of Kirkwoods dipole correlation factor clearly reveals the differences between isomers. It is proposed that the principal effect of pressure is to perturb the liquid structure. A model of intermolecular association involving monomeric, linear chain, and ring‐dimer species is developed and thermodynamic parameters characterizing the various intermolecular associative equilibria are evaluated. ΔH of association is nearly independent of pressure. Thus, application of pressure favors formation of linear chains primarily because of entropic factors. The nature of the shor...

Study of the Pressure Dependence of Dielectric Polarization

The pressure dependence of the dielectric polarization of polar fluids depends principally on three factors: (1) the fluid density, which is easily measured; (2) pressure‐induced distortion of molecules, expressed as dμ0u2009/u2009dP; and (3) pressure‐induced changes in the liquid structure, expressed as dgu2009/u2009dP, where g is Kirkwoods dipole correlation factor. d(gμ02)u2009/u2009dP has been determined over a wide range of temperature to 4 kbar for n‐propanol, sec‐butanol, and 6‐methyl‐3‐heptanol and is found to be either positive or negative depending on the temperature and the specific nature of the alcohol. At temperatures and pressures where g is near unity, increasing pressure enhances gμ02 because of pressure‐induced chain association; when g is already large, increasing pressure decreases gμ02. Determination of the dipole moment in dilute hexane solution as a function of pressure shows that for diethyl ether and n‐butyl chloride, μ0 is virtually constant to 4 kbar, μ0 of sec‐butanol probably increases slightly, and...

Viscosity of Isomeric Octyl Alcohols as a Function of Temperature and Pressure

The viscosity of 2‐ and 3‐octanol and 6‐methyl‐3, 5‐methyl‐3‐, and 2‐methyl‐3‐heptanol has been measured as a function of temperature (−20°–80°C) and pressure (0–4 kbar). Specific structural differences exist in the temperature and pressure coefficients of isobaric viscosity; these differences are minimized, but still exist, when isochoric viscosities are compared. Viscous flow and dielectric relaxation of these liquids are compared, and it is concluded that the rate‐determining steps are dissimilar. A previously proposed pressure‐induced liquid structure transformation in these liquids could not be verified viscometrically.

Evidence for Structural Transformation in Liquid Octyl Alcohols from PVT Studies

The densities of 2‐ and 3‐octanol and 2‐ and 5‐methyl‐3‐heptanol have been measured over a wide range of temperature and pressure. The isochoric P–T loci of 2‐ and 3‐octanol show definite inflections; those of the latter two compounds are linear in the range of measurement. The data are discussed in terms of a structural transformation involving H‐bonded linear chains, dimer rings, and monomer and it is proposed that the inflections characterize the transition from chains to rings and monomer. The proposition is supported by reference to dielectric data and the difference between the two sets of compounds is discussed.

Dielectric properties of isomeric phenyl propanols

Abstract The dielectric constant and loss of 1-phenyl-1-, 1-phenyl-2-, 2-phenyl-2-, and 3-phenyl-l-propanol have been measured as a function of temperature for f < 0.5 MHz. The equilibrium polarization depends markedly on the proximity of the phenyl and hydroxyl groups, apparently as a steric factor and not because of any specific OH-phenyl interaction. Dielectric relaxation in these liquids can be described in terms of overlapping Debye regions but for the most sterically hindered species the regions overlap so closely that the Davidson-Cole skewed-arc function becomes a more useful description. Activation energies depend on the degree of steric hindrance; this suggests that H-bond breaking is not the rate determining step in the relaxation mechanism

Dielectric study of the pressure-dependence of intermodular association

Equilibrium dielectric constants and densities of 3-octanol, 2-octanol, 2-methyl-3-heptanol, and 5-methyl-3-heptanol (hereafter referred to as 7;3, 7;2, 2;3, and 5;3, respectively) were measured as a function of pressure to 4 kb from about 100° to the respective freezing points. This study was undertaken in an effort to understand the nature and pressure dependence of the short-range order in these hydrogen-bonded liquids.