(144c) Steric Hindrance Effect on Adsorption Kinetic of Asphaltenes on Oil/Water Interfaces

Authors: 
Darjani, S., The City College of New York
Pauchard, V., City College of New York
Koplik, J., Levich Institute, City College of New York
Banerjee, S., City College of New York
Many equations of state such as Langmuir and Volmer model were introduced over the years to describe the adsorption behavior of a system, however, not all of them are able to capture the phase transition. On the other hand, Lattice gas model can capture the phase transition but not the adsorption isotherm.

Herein, the equation of state of a 2D hard-core lattice gas is studied with a new numerical method based on random sequential adsorption incorporating surface diffusion (RSAD) to obtain both phase transition and adsorption kinetic. From the success rate of adsorption attempts, a blocking function is extracted that can be used to obtain the dependency of surface pressure on surface coverage based on Gibbs adsorption isotherm. This model is used to analyze the interfacial behavior of asphaltenes at the water/oil interface. RSAD method generates accurate information, particularly through the calculation of correlation functions and the visual observation of the lattice structure at high coverage which reveal the phase transition of asphaltenes laden interface from disordered to ordered phase at high coverage due to the steric hindrance effect. This ordered phase is consistent with the observation of birefringence within asphaltenes laden interfaces upon contracting the aged droplet. Corresponding surface pressure obtained from this model is equal to the surface pressure that a droplet containing of asphaltenes solution loses its Laplacian shape over contraction experiment. Another outcome of this model is the observation of dynamic frustration within the dense interfacial layers due to the fast increase of surface coverage in comparison with interfacial diffusion either during spontaneous adsorption or during interfacial area reduction. As a result, the interfacial layer would enter into a metastable glass state that would slowly relax towards a crystalline state with time.