ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 17, Number 2
JKCSEZ 17(2)
April 20, 1973 

The ultrasonic absorption of Dodecyl pyridinium bromide (D.P.B.) in aqueous solution has been measured at 20℃ over a range of frequencies between 0.1 mc and 90 mc and a range of concentrations from 5 to 100 mM. The excess absorption was observed only in the solutions the concentration of which was higher than the critical micellar concentration (c.m.c.) both in the presence and absence of salt. The excess absorption of sound and the relaxation frequencies obtained from the absorption curves show a discontinuity with the variation of the concentration of D.P.B. in the neighborhood of 60 mM. Other properties such as viscosity, conductivity and velocity of sound also exhibit such a change near the same concentration. It is concluded that a change in the properties of the micelles of D.P.B. occurs in the neighborhood of this concentration. The mechanism of the observed ultrasonic excess absorption in attributed to the reaction M2 ↔ M1 + 2Br- where M2 and M1 are two types of micelles. The rate constants of forward and backward reactions are found to be 6.9 × 105sec-1and 6.7 × 1010mole-2sec-1 respectively. Some kinetic characteristics including free energy, enthalpy, entropy and activation energy were calculated.