Molecular relaxation processes of some halonaphthalenes in a polystyrene matrix

Abstract

The dielectric absorption of eight halonaphthalenes in a polystyrene matrix has been measured in the frequency range of 102–105 Hz and in two cases also in the range of 2.2×104 to 5×107 Hz and the enthalpy of activation for the molecular relaxation process determined by using the Eyring rate expression. The relaxation time and enthalpy of activation vary as the inclination of the dipole to the principal axes is altered. In fact, the relaxation time is appreciably longer for the 2- than the 1-halonaphthalenes while the enthalpies of activation of the latter range between 18–22 kJ mol−1 and for the former 23–41 kJ mol−1. The enthalpy variation between the 1- and 2-halonaphthalenes is to be contrasted with the behavior of quinoline and isoquinoline in Nujol solution where the solute molecules have virtually identical enthalpies of molecular reorientation.

Dielectric absorption of a few aromatic amines in a polystyrene matrix

“…3) are slightly asymmetrical, being somewhat steeper on the low frequency side. This is to be contrasted with the symmetrical curves observed for various rigid molecules where there is just one process (14). A reasonably linear Eyring plot yields AHE and ASE of 17 kJ mol-I and 26 J K-' mol-I respectively which are to be compared with the corresponding values of 11 kJ mol-I and -405 K-I mol-I for chlorobenzene in polystyrene.…”

“…Dielectric measurements on solutes dispersed in a polystyrene matrix and the evaluation of the results have been described previously (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). The polystyrene matrix was prepared in the way described by Davies and Swain (10).…”

“…(5) The enthalpy of activation for the molecular relaxation of a solute in polystyrene is highly dependent on size for a particular type of solute molecule (14). Thus, for the series chlorobenzene, 4-chlorotoluene, and 4-chlorobiphenyl (see Table l), the AH, values are l l , 2 9 , and 85 kJ mol-I respectively.…”

“…disk containing the solute (10,11,14). When the concentration of the solute in the polystyrene matrix is low (< 5 to 7 mol%), the AH, value for the molecular process is independent of concentration (27).…”

Broad band absorption of solutes in liquid solutions and in polystyrene

“…In the latter state the relaxation times of the molecules and of their substituent groups are very much longer than in liquid solutions. Studies of the dielectric relaxation processes of polar n~olecules in polystyrene matrices have been reported (14)(15)(16)(17), and we have previously carried out such studies for the four solutes (acetophenone, 1,4-diacetylbenzene, 4-acetylbiphenyl, and 6nitrobiphenyl) used in the present work (18).…”