| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 99 === This study investigates the adsorption kinetics of cationic surfactant 1-dodecylamine (DDA) and heptadecafluoro-1-nonanol. We measured the dynamic and equilibrium surface tension by using the pendant bubble tensiometer and surface tensiometer (CVBP-A3), then discussed the relaxations of surface tension at different surfactant concentrations.
There exists a plateau at surface tension γ = 43.7 mN/m in the dynamic surface profiles of aqueous DDA solutions at 25oC. This plateau phenomenon implies the existence of a phase transition for the DDA molecules adsorbed at air-water interface. Another novel phenomenon was also observed, that γ(t) decreases from 72 mN/m (the surface tension of solvent) since the generation of the air-water interface, reaches a minimum γ, then γ(t) increases with time. At the end of the adsorption process, γ(t) always comes back to 72 mN/m. This γ(t) data implies that the DDA molecules prefer to adsorb on quartz surface instead of the air-water interface. To clarify this point, we added a lot of quartz, glass or stainless steel beads into aqueous DDA solutions and measured their equilibrium surface tensions. The surface concentrations for DDA adsorbed on quartz, glass and stainless steel surface were then evaluated from the change of equilibrium surface tension based on the mass balance calculation.
At the end of this study, the adsorption kinetics of heptadecafluoro-1-nonanol (C9H2F17OH) onto a clean air-water interface was studied; relaxation profiles of surface tension for heptadecafluoro-1-nonanol molecules absorbing onto a freshly created air-water interface were obtained. The adsorption of fluoroalcohol C9H2F17OH was found to be cooperative from the equilibrium surface tension data at γ(C) > 65 mN/m compared with the prediction of the generalized Frumkin model. The controlling mechanism of the adsorption process was found to be mixed diffusive-kinetic controlled.
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