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

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R12HTAB) and n-hexane were measured using the spinning drop method. The effects of the R12HTAB 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, Da, and the adsorption barrier, ɛa, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while ɛa becomes higher with increasing R12HTAB concentration in the bulk aqueous phase. Da decreases from 5.56 × 10−12 m−2 s−1 to 0.87 × 10−12 m−2 s−1 while ɛa increases from 5.41 kJ mol−1 to 7.74 kJ mol−1 with the increase of concentration in the bulk solution of R12HTAB from 0.5 × 10−3 mol dm−3 to 4 × 10−3 mol dm−3. Change of temperature affects the adsorption rate through altering Da and ɛa. The value of Da increases from 5.56 × 10−12 m−2 s−1 to 13.98 × 10−12 m−2 s−1 while that of ɛa 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.