2020/07/31 by Pierre‐Michel Déjardin, Déjardin, Pierre-Michel, Florian Pabst +11
Chemical Engineering · Chemistry · Materials Science · Physics and Astronomy · #Advanced Physical and Chemical Molecular Interactions #Chemical and Physical Properties of Materials #FOS: Physical sciences #Other Condensed Matter (cond-mat.other) #Scientific Research and Discoveries #Soft Condensed Matter (cond-mat.soft) #Spectroscopy and Quantum Chemical Studies #Surfactants and Colloidal Systems #Thermodynamic properties of mixtures
paper · pdf · doi:10.48550/arxiv.2007.16026
openalex publication_date 2020/07/31 · openalex created_date 2022/07/26 · openalex updated_date 2026/07/28
An exact integral formula for the Kirkwood correlation factor of isotropic\npolar fluids gK is derived from the equilibrium averaged rotational Dean\nequation, which as compared to previous approaches easily lends itself to\nfurther approximations. The static linear permittivity of polar fluids\n\ε is calculated as a function of temperature, density and molecular\ndipole moment in vacuo for arbitrary pair interaction potentials. Then, using\nthe Kirkwood superposition approximation for the three-body orientational\ndistribution function, we suggest a simple way to construct model potentials of\nmean torques considering permanent and induced dipole moments. We successfully\ncompare the theory with the experimental temperature dependence of the static\nlinear permittivity of various polar fluids such as a series of linear\nmonohydroxy alcohols, water, tributyl phosphate, acetonitrile, acetone,\nnitrobenzene and dimethyl sulfoxide, by fitting only one single parameter,\nwhich describes the induction to dipole-dipole energy strength ratio. We\ndemonstrate that comparing the value of gK with unity in order to deduce the\nalignment state of permanent dipole pairs, as is currently done is in many\nsituations, is a misleading oversimplification, while the correct alignment\nstate is revealed when considering the proper interaction potential. Moreover\nwe show, that picturing H-bonding polar fluids as polar molecules with\npermanent and induced dipole moments without invoking any specific H-bonding\nmechanism is in many cases sufficient to explain experimental data of the\nstatic dielectric constant. In this light, the failure of the theory to\ndescribe the experimental temperature dependence of the static dielectric\nconstant of glycerol, a non-rigid polyalcohol, is not due to the lack of\nspecific H-bonding mechanisms, but rather to an oversimplified model potential\nfor that particular molecule.\n