Rotational Relaxation in Fluids

Abstract

In this paper a number of expressions for angular momentum and reorientation correlation times are obtained. The inverse of the angular momentum correlation time is related to a sum of two terms, one of which involves the shear viscosity of the medium and the other of which describes the precessional relaxation of the molecule. The derivation is based on the similarity of the time dependences of the torque and the force exerted on the molecule of interest. The reorientation correlation time is related to the angular momentum relaxation time in the diffusion and the near-diffusion limits. The expressions obtained here have been confirmed by a number of ESR experiments.

An electron resonance investigation of molecular motion in the smectic A mesophase of a liquid crystal

“…Experimentally K is observed to deviate from unity ; it is however found to be independent of both temperature and pressure although markedly solvent dependent [24]. These results have been rationalized by a theory [23] which relates K to the intermolecular torque .F and the intermolecular force 9, in fact according to this theory --Kii = (3/4Yo")(F-,"/.F"),…”

“…We shall now attempt such an analysis. A combination of experimental [22] and theoretical [23] investigations has shown that the principal components of the diffusion tensor are often given by PI Di = kT/8n-vaiKii.…”

A Study of the Effect of Solvent and Temperature on the Electron Paramagnetic Resonance Parameters and Linewidths of Copper(II)bis(Diethyldithiocarbamate)

“…V = KV,. Kivelson and co-workers (29,30) have devised a theory which shows that K can be expressed as the ratio of the mean square torques to the mean square forces experienced by the spin-probe:…”

“…Kivelson and co-workers (22,29,30) anisotropic interaction parameter, K , which lies between zero and unity such that V = 4 n r O 3~/ 3 . Thus the further K is from unity the more anisotropic is the potential in which the solute moves i.e.…”

Nuclear magnetic resonance spin–lattice relaxation and the rotation of adamantane and hexamethylenetetramine in solution

“…Gierer and Wirtz (5) argued that the molecule changes the viscosity of the fluid in its neighbourhood to q ' = KII and give a procedure for calculating the 'microviscosity factor', K, which is not very successful in practice (6). Kivelson et al (7) have given the expression relating K to the mean-square torque, ( T~) , and mean-square force, ( F~) , on the molecule; which is as yet untested due to the difficulties in determining the latter two quantities from realistic potentials. It seems best at this stage to regard K as an empirical parameter, with K = 1 representing the usual 'stick' condition and K = 0 the 'slip', or inertial, condition.…”