Pressure dependencies of rotational, translational, and viscous friction coefficients in waterhyphen;d2, acetonitrilehyphen;d3, acetonitrile, chloroform, and benzene

摘要

Molecular rotational friction coefficients (zgr;) were determined for neat waterhyphen;d2, neat acetonitrilehyphen;d3, neat acetonitrile, a 15percnt; solution of chloroformhyphen;d1in chloroform, and a 3percnt; solution of benzenehyphen;d6in benzene by measuring2H and14N nuclear magnetic resonance spinndash;lattice relaxation times as a function of pressure (0.1ndash;300 MPa). The pressure dependencies of the rotational zgr; values were obtained from the singlehyphen;body rotational correlation times for deuterated molecules in each liquid. The pressure dependencies were compared with those of the translational and viscous zgr; values derived, respectively, from the known selfhyphen;diffusion coefficients and viscosities. In such simple molecular liquids as chloroform and benzene, the translational and viscous zgr; values had almost the same pressure coefficient or activation volume, whereas the rotational zgr; values had considerably smaller pressure coefficients. The fractional viscosity (eegr;) exponent agr; in the phenomenological linear relation between zgr; and eegr;agr;was 0.9 for the translational zgr; in acetonitrile and 0.4ndash;0.6 for the rotational zgr; in acetonitrile (tumbling motion), chloroform, and benzene. Water was found to be exceptional because the pressure dependence of zgr; depended more strongly on the modes of molecular motions. The deviation of the viscosity exponent from unity clearly indicates a breakdown of the Stokesndash;Einsteinndash;Debye law with respect to pressure variations. The viscosity exponent is not universal, but specific to intermolecular interactions and therefore dependent on the liquid structure.