Study of the emulsion droplet collisions with the polarizable water/1,2-dichloroethane interface by the open circuit potential measurements

• Published in: Electrochimica acta Vol. 299; pp. 875 - 885
• Main Authors: Trojánek, Antonín, Samec, Zdeněk
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 10-03-2019; Elsevier BV
• Subjects: Charge transfer; Coalescing; Collisions; Dichloroethane; Droplets; Emulsion droplet; Emulsion stability; Flocculation; OCP transient; Open circuit voltage; Sedimentation; Single collision; Size distribution; Stability; Surface tension; Water/DCE interface; Single collision; Emulsion droplet; Water/DCE interface; OCP transient; Emulsion stability
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2019.01.041

The open circuit potential (OCP) measurements are used to study the single collisions of the DCE-in-water emulsion droplets containing an electrolyte (tetradodecylammonium chloride, TDDACl) with the polarizable water/1,2-dichloroethane (DCE) interface. The OCP transients exhibit a series of the potential spikes, which consist of the initial negative potential step followed by a slower relaxation of the potential to its original value. A novel mechanism of the collisions is proposed including the interpretation of the potential response shape. Low stability of the emulsion system precluded a convincing comparison of the OCP and DLS data, though in some cases the size distributions obtained by OCP and DLS measurements may coincide. A comparison of the interfacial tension or capacitance curves measured in the absence and presence of the emulsion droplets indicates that their specific adsorption at the water/DCE interface is negligible. The mean droplet diameter exhibits a monotonic increase with the increasing droplet concentration and time pointing to an increasing effect of the flocculation and coalescence. The change of the collision frequency with the emulsion droplet concentration can be rationalized by using a steady-state diffusion transport model, which predicts that the collision frequency scales down with the fourth power of the droplet diameter. The droplet size distribution is not much affected by a change in the TDDACl concentration, which leads to the proportional change of the total charge integrated from all the emulsion droplet collisions. However, the total charge itself represents only a small fraction of the charge theoretically available, which suggests that a large portion of the collisions are accompanied by the zero-net charge transfer of the neutral ion pair TDDA+Cl−, and/or a number of the droplets are lost through their accumulation on the glass walls of the experimental system. The DCE-in-water emulsion exhibits a very low stability, which is manifested primarily by a strong effect of the droplet concentration on the mean droplet diameter or by its increase with time, as well as by a difference in the droplet size distributions averaged over different time spans. Breakdown of this emulsion system seems to occur through a combination of the flocculation, coalescence and sedimentation. Nevertheless, the OCP measurements provide a valuable insight into its interfacial dynamic behavior.
•OCP transients reflect single emulsion droplet collisions with the water/DCE interface.•Novel mechanism of the droplet collisions with the water/DCE interface is proposed.•Effects of concentrations of the droplets and of their electrolyte content are examined.•Changes of collision frequency are rationalized using a diffusion transport model.•Low stability of the emulsion droplets is manifested.