![]() This also correlates very well to the very low CMC of Tween 80. For the non-ionic surfactant, the kinetics of interfacial tension is seen to be already very slow and the addition of salt does not influence it further. This change is however not able to account for the slowing down of adsorption dynamics we find that it is rather the decreases of the monomer concentration (CMC) in the presence of salt which has the major influence. Sum Frequency Generation surface spectroscopy experiments and the equilibrium adsorption measurements show that the presence of NaCl in CTAB solution leads to the formation of ion-pairs at the surface thereby neutralizing the charge of the head group of CTAB. For the ionic surfactant, the dynamics agree with the usual diffusion limited interfacial adsorption kinetics however, the kinetics become orders of magnitude slower when NaCl is present. ![]() ![]() Dynamic surface tension measurements allow comparing the surface tension as a function of time for pure surfactant solutions and in the presence of NaCl. Equilibrium surface tension measurements show that NaCl significantly reduces the critical micellar concentration (CMC) of CTAB but has no effect on the CMC of Tween 80. We study the influence of high NaCl concentrations on the equilibrium and dynamic surface tensions of ionic (CTAB) and non-ionic (Tween 80) surfactant solutions.
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