A Simple Method for Estimation of Dielectric Constants and Polarizabilities of Nonpolar and Slightly Polar Hydrocarbons

Abstract

Many of the liquids that are used as electrical insulators are nonpolar or slightly polar petroleum-derived hydrocarbons, such as the ones used for cable and/or transformer oils. In this work, semi-empirical expressions with no adjustable parameters for the dielectric constant and the polarizability of nonpolar and slightly polar hydrocarbons and their mixtures are proposed and validated. The expressions that were derived using the Vargas-Chapman One-Third rule require the mass density and the molecular weight of the substance of interest. The equations were successfully tested for various hydrocarbons and polymers with dipole moments <0.23 and densities from 500 to 1200 kg·m −3 . The predictions are in good agreement with the experimental data in a wide range of temperatures and pressures. The proposed expressions eliminate the need of extensive experimental data and require less input parameters compared to existing correlations.

Accurate Estimation of Membrane Capacitance from Atomistic Molecular Dynamics Simulations of Zwitterionic Lipid Bilayers

“…As clearly shown there, they show good agreement with the corresponding experimental values. Furthermore, the best fit for ε h using a linear regression model led to a value of ε h = 2.01 that is consistent with experimentally derived values for alkanes …”

“…Furthermore, the best fit for ε h using a linear regression model led to a value of ε h = 2.01 that is consistent with experimentally derived values for alkanes. 25 Notably, the computed bilayer thicknesses d b show a poor match with the experimental data obtained from X-ray experiments ( Table 2). This suggests that the "membrane capacitor thickness" of the bilayer is different from simply the physical thickness of the hydrocarbon chains, possibly as a result of molecular interactions arising in the lipid bilayer at the interface between the hydrophobic and hydrophilic regions.…”

“…22 While this approach has potential, it relies on several untested assumptions: first, that a slab model faithfully describes the dielectric profile of a lipid bilayer; second, that the contribution of the phospholipid head groups (ε P ≈ 10− 30) 23,24 to the total capacitance is negligible; third, that the thickness of the bilayer hydrophobic core is precisely known; and fourth, that the relative dielectric of the membrane interior can be considered to be identical to that of alkanes, with values of around 2.0−2.1. 25,26 Recently, Garten et al 27 managed to measure for the first time the capacitance of solvent-free lipid bilayers using GUVs. Using a fitting procedure based on a uniform slab model, they found that their capacitance measurements led to a value of 2.06 for the dielectric constant of the bilayer interior ε h and observed a good correlation between membrane capacitance and bilayer thickness measured using X-ray form factors.…”

“…While this approach has potential, it relies on several untested assumptions: first, that a slab model faithfully describes the dielectric profile of a lipid bilayer; second, that the contribution of the phospholipid head groups (ε P ≈ 10–30) , to the total capacitance is negligible; third, that the thickness of the bilayer hydrophobic core is precisely known; and fourth, that the relative dielectric of the membrane interior can be considered to be identical to that of alkanes, with values of around 2.0–2.1. , …”