Study on dynamic interfacial tension of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide at liquid/liquid interface

Abstract

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R 12HTAB) and n-hexane were measured using the spinning drop method. The effects of the R 12HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, D a, and the adsorption barrier, ɛ a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while ɛ a becomes higher with increasing R 12HTAB concentration in the bulk aqueous phase. D a decreases from 5.56 × 10 −12 m −2 s −1 to 0.87 × 10 −12 m −2 s −1 while ɛ a increases from 5.41 kJ mol −1 to 7.74 kJ mol −1 with the increase of concentration in the bulk solution of R 12HTAB from 0.5 × 10 −3 mol dm −3 to 4 × 10 −3 mol dm −3. Change of temperature affects the adsorption rate through altering D a and ɛ a. The value of D a increases from 5.56 × 10 −12 m −2 s −1 to 13.98 × 10 −12 m −2 s −1 while that of ɛ a decreases from 5.41 kJ mol −1 to 5.07 kJ mol −1 with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules.