Heterogeneity of Asphaltene Deposits on Gold Surfaces in Organic Phase Using Atomic Force Microscopy

Abstract

Atomic force microscopy (AFM) was used to measure the heterogeneity of asphaltenes adsorbed on gold for pentane-to-oil ratios (S/O) ranging from 0 to 0.5. Both adsorption of asphaltenes and AFM measurements were conducted in the same solvent mixture of toluene and pentane. The averaged approach and retraction heights of the deposited asphaltene material increased from 2 nm on washed surfaces to 8 nm for S/O = 0.43. The average adhesion forces during retraction of the AFM tip were greater than zero for S/O > 0.2. Repetition of the approach and retraction measurements at different locations on gold substrates showed that the deposited asphaltene aggregates are heterogeneous in height and elasticity. The extent of the heterogeneity is more evident at the onset of asphaltene precipitation (S/O = 0.43).