Abstract
The ultrasonic absorption of Dodecyl pyridinium bromide (D.P.B.) in aqueous solution has been measured at $20^{\circ}C$ 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 $M_2{\rightleftarrow}M_1+2Br^-$where$M_2$ and$M_1$are two types of micelles. The rate constants of forward and backward reactions are found to be $6.9 {\times} 10^5 sec^{-1)$and $6.7{\times}10^{10}sec^{-1}mole{-2}$ respectively. Some kinetic characteristics including free energy, enthalpy, entropy and activation energy were calculated.
界面活性劑 dodecyl pyridinium bromide(D.P.B.) $20^{\circ}C$ 濃度 5∼100mM 水溶液中에서 0.1Mc~90Mc 超音波의 吸收 係數를 測定정하였다. 監 存在 與否에 關係없이 臨界 micelle 濃度(c.m.c.)以上의 濃度에서만 超音波超過 吸收가 觀測되었다. 超音波 吸收 曲線에서 D.P.B.水溶液 60mM附近에 超過 吸收 및 relaxation 振動數의 不連續的인 變化를 觀測하였다. 또 粘性係數, 電氣傳導度, 超音破速度들의 濃度曲線 에서도 같은 濃度에서 不連續的인 變化를 나타낸다. 따라서 이 濃度 附近에서 D.P.B.의 micelle의 性質에 變化가 일어나고 있다고 結論지을 수 있다. 超音波超過 吸收의 mechanism은 $M_2{\rightleftharpoons}M_1+2Br^-$ 反應에 基因됨을 알았다. 여기서 $M_2$,$ M_1$은 다른 型의 micelle이다. 正, 逆方向의 反應速度常數는 各各 $6.9 {\times} 10^5 sec^{-1)$, $6.7{\times}10^{10}sec^{-1}mole{-2}$임이 觀測되었다. 이 反應 mechanism의 自由 에너지, enthalpy, entropy 및 活性化에너지를 算出하였다.