**1. Introduction**

The dynamics of adsorption-desorption of soluble surfactants at water-air interfaces play a very important role in many phenomena and technological applications such as wetting, detergency, emulsification, and foaming [1–4]. These processes express themselves in the time-dependent surface properties, such as surface tension (dynamic surface tension) and surface dilatational [3] and shear rheology [4]. Although, the phenomenon has been extensively studied, the physics of the adsorption-desorption dynamics of surfactants at fluid-fluid interfaces is far from completely understood [5]. For ionic surfactants, the adsorption dynamics deviates from the diffusion limited model developed by Ward and Tordai [6] in the 1940s. The origin of these deviations can be found in the presence of electrostatic adsorption barriers [7–10]. In a previous paper [10] we studied the adsorption kinetics of a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), using dynamic surface tension measurements. It was found that the adsorption dynamics is controlled by diffusion (DLA) at very short adsorption times but it is kinetically limited (KLA), at times close to the equilibrium, by an electrostatic barrier built-up, as the ionic surfactant molecules adsorb onto the interface. In another very recent article, we explain the appearance of negative surface viscosities for a cationic Gemini surfactant, dimethylene-1,2-bis(dodecyldimethylammonium) bromide (G12-2-12), by the asymmetries found in the adsorption-desorption processes and dynamics [11]. The unphysical result (negative viscosities) is just an artifact due to the procedure used for data analysis, which is invalidated by the existence of those asymmetries.

In this article, we extend the study on G12-2-12 by systematically measuring the dynamic surface tension and time-resolved surface potential, trying to shed light on those processes, their origin, and mechanisms. We used the maximum bubble pressure technique in order to access the very short intermediate adsorption times and Wilhelmy plate technique [12], in order to study the long adsorption time dynamics and to obtain the equilibrium values. We explored the whole range of surfactant concentrations, from very dilute to twice the critical micelle concentration, cmc, of the surfactant. As mentioned, we also performed time-resolved surface potential measurements in the hope to elucidate the role played by charge redistribution within the interface, in the adsorption dynamics and the corresponding evolution of surface tension. We found very complex behavior, with several characteristic times, both for the dynamic surface tension and surface potential. For the more dilute solutions, the initial adsorption step is controlled by diffusion (DLA), and in the last part, close to the equilibrium, the adsorption is kinetically limited (KLA). Between those extremes, the adsorption involves several processes with different characteristic times, where the redistribution of charges at the interface is evident. The existence of these numerous processes is compatible with the observation of several characteristic times in compression surface rheology experiments [11]. The results presented here shed light on the role played by charge organization on the dynamics of adsorption of ionic surfactants.
