Rotational friction coefficients for ellipsoids and chemical molecules with the slip boundary condition

Abstract

Friction coefficients are calculated numerically for ellipsoids rotating about their principal axes and for a benzene molecule rotating normal to its axis of symmetry under conditions of creeping flow and slip boundary conditions. It has been shown previously, that if a benzene molecule is approximated by an oblate spheroid, the predicted and experimental friction coefficients differ by more than 40%. The present study employs a more realistic shape for benzene and finds a difference of 10%, which is within the limits of the numerical and experimental uncertainty.

Influence of temperature and viscosity on anthracene rotational diffusion in organic solvents: Molecular dynamics simulations and fluorescence anisotropy study

“…The experimentally determined rotational relaxation times agree well with slip predictions for axial ratios 1:0.6:0.4 ͑solid line͒ and 1:0.7:0.3 ͑dashed line͒ and a volume of 223 Å 3 . 23,24 Although the data shown in Fig. 12 roughly follow slip boundary conditions, a single parameter ͑the viscosity͒ clearly cannot account completely for the observed solvent dependence.…”

“…Finally, to correlate our results with theoretical models of rotational diffusion, we used the predicted values of D r,x , D r,y , and D r,z for a triaxial ellipsoid under slip conditions 23,24 to obtain relaxation times based on hydrodynamic theory.…”

“…19,20 Numerical results were obtained for biaxial 21,22 and triaxial ellipsoids under slip conditions. 23,24 Translational diffusion coefficients were determined analytically for a sphere 18 and a triaxial ellipsoid 19,20 under stick conditions. More recently numerical results for arbitrary shapes have also been obtained.…”

Rotational Dynamics of Nonpolar and Dipolar Molecules in Polar and Binary Solvent Mixtures

“…Of these, molecular reorientation of molecules in solution has been an important experimental and theoretical concept for probing the nature of liquids and the interactions of solvents with molecules. This has proven to be among the most useful because of the combined generality of the effect and the well-developed theoretical framework for the interpretation of the experimental data (Debye, 1929;Perrin, 1936;Chuang and Eisethal, 1972;Hu and Zwanzig, 1974;Youngren and Acrivos, 1975;Zwanzig and Harrison, 1985). Though, the effect of solute-solvent interactions on the rotational motion of a probe molecule in solution has been extensively studied, these interactions are generally described as friction to probe rotational motion and can be classified into three types.…”

Depolarized Rayleigh light scattering studies of concentrated aqueous nitrate solutions

“…Calculations using the slip ,,odel of ',t:)I ional diffUsi')n for prolate and oblate ellipsoids have been reported by (19) and for generalized ellipsoids by Youngren and Acrivos (20).…”