Analytical model for zeta potential of asphaltene

In this paper, we provide for the first time an analytical framework for calculating the zeta (ζ) potential of asphaltene in aqueous solution in presence and in absence of an electrolyte salt. The analytical model is based on the assumption that the ionizable (in aqueous solution) carboxylic and hydroxyl groups present on the asphaltene molecule lead to its charging. The model predicts the ζ potential as a function of parameters such as buffer pH and electrolyte salt concentration. For the case with the added salt, ζ potential decreases with pH monotonically, and we obtain quantitative match with the experimental results. For the case without the added salt, the variation with pH is non-monotonic, represented by presence of two distinct extrema, and can be attributed to the role of the corresponding Electric Double Layer (EDL) thickness, which (in absence of any added salt) is a sole function of the pH.